Positioning device, speed measurement device, and positioning method

Abstract

To provide a positioning device, a speed measurement device, and a positioning method capable of further improving measurement accuracy.SOLUTION: A positioning device according to an embodiment is a positioning device that measures the position of a vehicle and comprises a first positioning unit, a second positioning unit, and a determination unit. The first positioning unit receives positioning signals from satellites and measures a first position of the vehicle. The second positioning unit measures a second position of the vehicle on the basis of the output from an autonomous positioning sensor. The determination unit sets the second position as the position of the vehicle in at least one of cases where the first position is within a range based on a prescribed position and a change in the traveling direction of the vehicle is a prescribed amount.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] Embodiments of the present invention relate to a position positioning device, a speed measurement device, and a position positioning method.

Background Art

[0002] For railway automatic operation, there is a demand for a device that simultaneously performs position positioning and speed measurement and for higher accuracy. For train position positioning, in-track detection within a signal section by passing a ground element is generally performed. Also, for speed measurement, a method of measuring speed by frequency conversion using a tachogenerator (hereinafter referred to as TG) is generally used.

[0003] There is also a method of positioning using a positioning radio wave signal transmitted from a satellite. However, in this case, due to problems such as multipath in the railway line environment, the measurement accuracy is up to ±10 m at maximum, and the measurement accuracy becomes low for position positioning for automatic operation. Also, there is a risk that the running position cannot be grasped even in areas where satellite reception is impossible, such as under elevated structures or underground sections like tunnels and elevated station buildings.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0005] To provide a position positioning device, a speed measurement device, and a position positioning method capable of further improving measurement accuracy.

Means for Solving the Problems

[0006] The positioning device according to the embodiment is a positioning device that measures the position of a vehicle, and includes a first positioning unit, a second positioning unit, and a determination unit. The first positioning unit receives a positioning signal from a satellite and measures the first position of the vehicle. The second positioning unit measures the second position of the vehicle based on the output of an autonomous positioning sensor. The determination unit sets the second position as the position of the vehicle when at least one of the following conditions is met: the first position is within a range based on a predetermined position, and the change in the traveling direction of the vehicle is a predetermined amount.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

Figure 18

Figure 19

Figure 20

Figure 21

Figure 22

Figure 23

Figure 24

Figure 25

Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings attached to this specification, for the sake of illustration and ease of understanding, the scale, the aspect ratio of the vertical and horizontal dimensions, etc. are appropriately changed and exaggerated from those of the actual object.

[0009] (First Embodiment) FIG. 1 is a schematic configuration block diagram of a traveling position detection system 10 according to the first embodiment. The traveling position detection system 10 is mounted on a railway vehicle 11 and is capable of performing positioning based on positioning radio wave signals SX1 to SX4 transmitted from transmitters of artificial satellites (hereinafter sometimes referred to as positioning satellites) 12-1 to 12-4. This traveling position detection system 10 includes a receiving antenna device 13, an external device 14, and a receiving arithmetic processing device (positioning device) 15. In this embodiment, the artificial satellites 12-1 to 12-n will be described with n = 4, but it is not limited thereto. For example, n may be a natural number of 5 or more.

[0010] The receiving antenna device 13 is an antenna device capable of receiving the positioning radio wave signals SX1 to SX4. The external device 14 is a device that performs traveling control of the railway vehicle 11 based on the positioning result, and is, for example, a train integrated management device (TCMS), a driver assistance control device for automatic driving, or an on-vehicle monitor. The receiving arithmetic processing device 15 performs positioning processing based on the positioning radio wave signals SX1 to SX4 output from the receiving antenna device 13 and outputs the positioning result to the external device 14.

[0011] FIG. 2 is a block diagram showing a configuration example of the receiving arithmetic processing device 15 according to the first embodiment. The receiving arithmetic processing device 15 includes a positioning signal arithmetic processing unit (first positioning unit) 21, a satellite reception control unit 22, an autonomous measurement arithmetic processing unit (first measurement unit) 23, a traveling state determination processing unit 24, a vehicle position correction unit (second positioning unit) 25, an autonomous measurement switching determination unit (determination unit) 26, a storage device 27, a communication connection device 28, and a positioning signal speed arithmetic unit (second measurement unit) 29. In FIG. 2, a three-axis sensor unit CSU is further illustrated. The three-axis sensor unit CSU is a three-axis sensor including, for example, a three-axis acceleration sensor, a three-axis gyro sensor, and a three-axis geomagnetic sensor.

[0012] The positioning signal arithmetic processing unit 21 calculates the position coordinates of the railway vehicle 11 based on the positioning radio signals SX1 to SX4 received by the receiving antenna device 13, and outputs a positioning data group DG. The positioning data group DG includes time, satellite orbit information (such as satellite almanac information and satellite ephemeris information) included in the positioning radio signals SX1 to SX4, the received signal strength of the positioning radio signals SX1 to SX4, and the position coordinates of the railway vehicle 11, etc.

[0013] The satellite reception control unit 22 performs arithmetic processing for estimating the position error based on the positioning radio signals SX1 to SX4 from the artificial satellites 12-1 to 12-4 and their signal strengths included in the positioning data group DG. Thereby, the satellite reception control unit 22 performs reception control such as the corresponding satellite reception elevation angle and reception strength based on the obtained estimated arithmetic error. The details of the satellite reception control unit 22 will be described later with reference to FIGS. 15 to 19.

[0014] The self-positioning arithmetic processing unit 23 outputs a self-positioning data group DS based on the output of the three-axis sensor unit CSU. The self-positioning data group DS includes time, speed, traveling vectors in three-axis directions, etc. That is, the self-positioning arithmetic processing unit 23 performs arithmetic processing on the speed and the traveling vectors in three-axis directions using a general arithmetic method. For example, the traveling vectors in three-axis directions are calculated by time-integrating the accelerations in three-axis directions based on the output of the three-axis acceleration sensor. Also, the speed can be calculated, for example, as the absolute value of the traveling vectors in three-axis directions.

[0015] The running state discrimination processing unit 24 mainly uses the self-positioning data group DS to discriminate the running state of the railway vehicle 11 (for example, the running state includes speed information and information indicating a stopped state). A detailed processing example of the running state discrimination processing unit 24 will be described later with reference to FIG. 20.

[0016] The vehicle position correction unit 25 corrects and calculates the position coordinates of the railway vehicle 11 based on the positioning data group DG using the information of the self-positioning data group DS, and outputs the position information of the railway vehicle 11. That is, the vehicle position correction unit 25 calculates the time-series change of the position coordinates of the railway vehicle 11 from the reference position using the information of the self-positioning data group DS. This reference position is the average position of the positions where positioning or self-calculation was performed in the past. For example, the reference position is the average value of the past 10 positioning positions when passing the same ground unit. A detailed processing example of the vehicle position correction unit 25 will be described later with reference to FIG. 21.

[0017] The self-positioning switching determination unit 26 determines which of the position coordinates output by the positioning signal calculation processing unit 21 and the position coordinates output by the vehicle position correction unit 25 is to be used as the position coordinates of the railway vehicle 11 according to at least one of the radio wave states of the positioning radio wave signals SX1 to SX4 and the position of the railway vehicle 11. For example, the self-positioning switching determination unit 26 uses the positioning data group DG to determine whether the railway vehicle 11 exists in an environment where it cannot capture the artificial satellites 12-1 to 12-4, and automatically switches to the self-positioning measurement process that mainly uses the position coordinates output by the vehicle position correction unit 25 when it exists in an environment where it cannot capture the artificial satellites 12-1 to 12-4. In addition, the self-positioning switching determination unit 26 stores in the storage device 27, together with the time, information indicating whether it is in the positioning calculation state (State1) that mainly uses the position coordinates output by the positioning signal calculation processing unit 21 or the self-positioning measurement process state (State2) that mainly uses the position coordinates output by the vehicle position correction unit 25.

[0018] The storage device 27 is realized by, for example, a semiconductor memory element such as a RAM (Random Access Memory), a flash memory, a hard disk, an optical disk, or the like. The storage device 27 stores various kinds of information. The communication connection device 28 communicates between the storage device 27 and the external device 14.

[0019] The positioning signal speed calculation unit 29 calculates the speed of the railway vehicle 11 using the radio waves of the positioning radio signals SX1 to SX4. In the railway vehicle 11, wheel spin or skidding may occur during acceleration and deceleration. Therefore, generally, the speed calculated using radio waves is more accurate than the speed based on frequency conversion by the speed generator (tacho generator) of the railway vehicle 11.

[0020] The positioning signal speed calculation unit 29 calculates the speed of the railway vehicle 11, for example, based on the Doppler effect of the carrier waves output from the artificial satellites 12-1 to 12-4. Since the carrier wave frequencies (L1 band fs = 1.5754 GHz) of the artificial satellites 12-1 to 12-4 are strictly managed, the speed V is calculated by measuring this frequency using Equation (1). On the other hand, since the artificial satellites 12-1 to 12-4 are moving at high speed, the ground speed cannot be obtained using only the carrier wave frequency of one artificial satellite. Therefore, the carrier wave frequencies from a plurality (for example, four or more) of artificial satellites 12-1 to 12-4 are measured, and the ground speed is calculated. Also, similar to the positioning signal calculation processing unit 21, when the railway vehicle 11 passes through the invisible region, it becomes impossible to measure the speed using the carrier wave frequency.

Equation

[0021] First, based on FIG. 3, a processing example of the positioning signal calculation processing unit 21 and the self-measurement calculation processing unit 23 will be described. FIG. 3 is a processing flowchart of the positioning signal calculation processing unit 21 according to the first embodiment.

[0022] The positioning signal calculation processing unit 21 of the reception calculation processing device 15 receives the positioning radio signals SX1 to SX4 via the reception antenna device 13 (step S11).

[0023] Next, the positioning signal arithmetic processing unit 21 extracts and acquires time signals from the positioning radio signals SX1 to SX4 (step S12). Subsequently, the positioning signal arithmetic processing unit 21 acquires position information including latitude information and longitude information based on satellite orbit information (for example, satellite almanac information and satellite ephemeris information) and the obtained time signals (step S13).

[0024] Here, the details of the method for acquiring the position information will be described. The positioning signal arithmetic processing unit 21 calculates the position coordinates (x, y, z) of the railway vehicle 11 using, for example, the orbit information from the artificial satellites 12-1 to 12-4. That is, it is possible to calculate the position coordinates (x, y, z) of the railway vehicle 11 based on the positions of the artificial satellites 12-1 to 12-4 and the information setting the distances between the artificial satellites 12-1 to 12-4 and the reception arithmetic processing device 15 at that instant. In this case, if there are three or more sets of information on the position of the artificial satellite and the distance between the artificial satellite and the reception arithmetic processing device 15 at that instant, the coordinates (x, y, z) can be calculated. For this reason, a fourth satellite is generally required to ensure the accuracy of the time.

[0025] More specifically, the positioning signal arithmetic processing unit 21 calculates the position coordinates (x, y, z) of the railway vehicle 11 by the following formula (2) based on the satellite orbit information (for example, satellite almanac information and satellite ephemeris information) and the obtained time signals.

[0026] (In formula (2), (x, y, z) are the parameter values of the coordinates of the position to be obtained, and (x n , y n , z n ) are the parameter values of the coordinates of the position of the satellite that transmits the positioning signal. Also, t is the parameter of the positioning time, and t n is the parameter of the time when the artificial satellites 12-1 to 12-4 transmit the positioning signal. Note that the positioning signal arithmetic processing unit 21 may receive the positioning signal via a ground base station or the like. The positioning signal arithmetic processing unit 21 calculates the position information to be detected using these four parameters by the least squares method or the like.

[0027]

Number

[0028] Subsequently, the positioning signal calculation processing unit 21 acquires the number of positioning satellites based on the calculation result (step S14). Further, the positioning signal calculation processing unit 21 calculates the elevation angle of the positioning satellite based on the satellite almanac information, and acquires information on the reception intensity at the time of receiving the positioning radio signals SX1 to SX4 from the receiving antenna device 13 (step S15). For example, the positioning signal calculation processing unit 21 can calculate the elevation angle of the positioning satellite from the relationship between the positions of the artificial satellites 12-1 to 12-4 and the position coordinates (x, y, z) of the railway vehicle 11.

[0029] Next, the positioning signal calculation processing unit 21 acquires the azimuth angle of the positioning satellite (step S16). For example, the positioning signal calculation processing unit 21 can calculate the azimuth angle of the positioning satellite from the relationship between the positions of the artificial satellites 12-1 to 12-4, the position coordinates (x, y, z) of the railway vehicle 11, and the direction of the railway vehicle 11. Further, the positioning signal calculation processing unit 21 acquires other satellite reception information (step S17). The positioning signal calculation processing unit 21 outputs a positioning data group DG including these pieces of information and stores it in the storage device 27.

[0030] Next, the self-positioning calculation processing unit 23 acquires the output of the three-axis acceleration sensor from the three-axis sensor unit CSU (step S18), acquires the output of the three-axis gyro sensor (step S19), and acquires the output of the three-axis geomagnetic sensor (step S20). The self-positioning calculation processing unit 23 calculates the speed and the traveling vector in the three-axis directions, outputs a self-positioning data group DS including these pieces of information, and stores it in the storage device 27 together with the time. At this time, the vehicle position correction unit (second positioning unit) 25 calculates the position coordinates of the railway vehicle 11 based on the self-positioning data group DS and stores it in the storage device 27 together with the time.

[0031] Here, with reference to FIGS. 4 to 8, the satellite reception control of the satellite reception control unit 22 and the self-positioning measurement switching determination process of the traveling state determination process unit 24 when the occurrence locations of reception failures of the positioning radio signals SX1 to SX4 due to tunnels or the like are known will be described. In the following, the same numbers are assigned to equivalent processes, and the description may be omitted in some cases.

[0032] FIG. 4 is a diagram schematically showing a processing environment when invisible regions B1 to B2 are set. The railway vehicle 11 travels on the track of the actual space line L1. Also, the railway vehicle 11 stores in advance the track information of the line L2 on the map and the information of the invisible regions B1 to B2. In FIG. 4, GNSS (Global Navigation Satellite System) sections S1 and S3, which are regions other than the invisible regions B1 to B2, and a self-positioning measurement section S2 corresponding to the invisible regions B1 to B2 are shown. In the present embodiment, the invisible regions B1 to B2 mean regions where reception failures of the positioning radio signals SX1 to SX4 occur.

[0033] FIG. 5 is a processing flowchart (part 1) of the satellite reception control process and the self-positioning measurement switching determination process.

[0034] As shown in FIG. 5, in the present embodiment, first, the traveling state determination process unit 24 acquires the positioning satellite elevation angle and reception intensity included in the positioning data group DG (step S31). Next, the position signal calculation processing unit 21 calculates the estimated position error, and the traveling state determination process unit 24 acquires the estimated position error (step S32). The position signal calculation processing unit 21 calculates a PDOP (Precision Dilution of Precision due to satellite geometry) value as the ranging accuracy. DOP (Dilution of Precision) is an index of the satellite arrangement state. The DOP value has a higher correlation with the positioning accuracy than the number of satellites, and generally, the smaller the value, the higher the positioning accuracy. This DOP value includes HDOP (Horizontal DOP) which indexes only the horizontal component of the geometric arrangement of satellites, VDOP (Vertical DOP) which indexes only the vertical component, PDOP (Position DOP) which synthesizes them, etc. In this embodiment, the PDOP value is used in normal measurement. On the other hand, when high accuracy is required for "height", the VDOP value may be used. Also, the traveling state determination processing unit 24 may use the EHPE (estimated horizontal positioning accuracy) calculated by the position signal calculation processing unit 21 as the estimated position error value.

[0035] Subsequently, the traveling state determination processing unit 24 sets the reception azimuth angle based on the traveling direction of the railway vehicle 11 acquired (step S33). The traveling direction of the railway vehicle 11 is calculated by the self-positioning calculation processing unit (second positioning unit) 23 based on the output signal from the three-axis sensor unit CSU. Note that the setting of the reception azimuth angle (step S33) is not necessarily performed at this stage.

[0036] Next, the traveling state determination processing unit 24 compares the measured reception intensity db with the reception intensity determination threshold db_thr stored in the storage device 27 (step S34).

[0037] If db_thr < db (Yes in step S34), it means that the reception intensity is sufficiently strong and the sensitivity is good, and the process transitions to the control of the satellite elevation angle of the satellite to be received.

[0038] Next, the traveling state determination processing unit 24 uses the predetermined PDOP determination threshold pdop_thr read from the storage device 27 to compare with the measured PDOP value (pdop) in order to determine whether elevation angle control is necessary (step S35).

[0039] When pdop ≥ pdop_thr (No in step S35), it means that the position accuracy degradation rate is high and the accuracy is in a relatively poor state. The driving state determination processing unit 24 causes the satellite reception control unit 22 to calculate the upper limit angle and the lower limit angle of the elevation angle (step S36) and perform elevation angle control (reset) (step S37). In this case, examples of the calculation method of the upper limit angle and the lower limit angle of the elevation angle include a method using parameters of a regression equation obtained from a predetermined elevation angle and an estimated position error stored in the storage device 27, a method using parameters of a regression equation obtained from the elevation angle and the PDOP value, and the like. Since these methods result in a relational expression in which the estimated position error is improved, any method can be used.

[0040] Next, the driving state determination processing unit 24 causes the processes of step S31 and step S32 to be performed in time series within a predetermined time range, and acquires the received signal strength and PDOP values in time series (step S38). Then, when a predetermined time has elapsed, the driving state determination processing unit 24 determines whether db1_thr < db1, div < div_thr, and pdop < pdop_thr (step S39). Here, db1 is the average value of the received signal strength, div is the variance of the received signal strength, and db1_thr and div_thr are the average of the received signal strength and the determination threshold of the received signal strength, respectively. For example, in the regions before and after the invisible regions B1 to B2 shown in FIG. 4, the variation in the received signal strength becomes large, and the received signal strength decreases within the invisible regions B1 to B2. Therefore, by evaluating the average and variance values of the received signal strength, it is possible to avoid elevation angle control (reset) before and after the invisible regions B1 to B2 and within the invisible regions B1 to B2 when the evaluation is low.

[0041] When db1_thr < db1, div < div_thr, and pdop < pdop_thr (Yes in step S39), the elevation angle is reset, and the process from step S31 is repeated. In this case, it is determined that the position accuracy degradation rate is not high and the signal strength of the satellites in the selected elevation angle range is high. Therefore, the upper limit angle and the lower limit angle of the elevation angle reset as the control values of the positioning satellite elevation angle and the reception intensity are changed, and the process from step S31 is repeated. At this time, the running state determination processing unit 24 stores in the storage device 27 that it is in the positioning calculation state (State1) along with the time. Also, since it is determined that the position accuracy degradation rate is not high and the signal strength of the satellites in the selected elevation angle range is high, the position coordinates calculated by the positioning signal calculation processing unit 21 and the speed calculated by the positioning signal speed calculation unit 29 can be preferentially used as the position information of the railway vehicle 11.

[0042] On the other hand, when db1_thr < db1 and div < div_thr, but pdop < pdop_thr (NO in step S39), it is determined that the quality of the received signals of the satellites in the selected elevation angle range is low. Therefore, the satellite reception control unit 22 is made to control (reset) the elevation angle (step S37), and the process from step S38 is repeated. When db1_thr > db1 or div > div_thr, it is determined that the radio wave reception environment is bad, so the determination of pdop < pdop_thr is not performed and the system waits.

[0043] In this way, when resetting the elevation angle, the signal strength of the satellites and the arrangement state of the satellites are confirmed, and the elevation angle is controlled (reset) when the communication state is good. Therefore, the upper limit angle and the lower limit angle of the elevation angle can be set with higher precision. By controlling the upper limit angle and the lower limit angle of the elevation angle in this way, it becomes possible to obtain a more accurate positioning signal.

[0044] On the other hand, when db_thr ≥ db (No in step S34), it means that the reception intensity is weak and the sensitivity is poor. The running state determination processing unit 24 transitions to the control of the reception intensity and the branch processing A of the self-positioning measurement processing.

[0045] FIG. 6 is a flowchart of the branch process A. As shown in FIG. 6, the running state determination processing unit 24 determines whether reception intensity control is necessary by determining whether the measured EHPE value (ehpe) is less than a predetermined EHPE determination threshold value ehpe_thr stored in the storage device 27 (step S41).

[0046] When ehpe < ehpe_thr (Yes in step S38), it means that the position accuracy degradation rate is low and the accuracy is relatively good, but the reception intensity is poor. The running state determination processing unit 24 causes the satellite reception control unit 22 to calculate the upper limit intensity and the lower limit intensity of the reception intensity (step S42), and performs control (reset) of the reception intensity (step S43).

[0047] In this case, for the calculation of the upper limit value and the lower limit value of the reception intensity, there are methods such as using the parameters of the regression equation obtained from the predetermined reception intensity stored in the storage device 27 and the estimated position error, and the parameters of the regression equation obtained from the reception intensity and the EHPE value. Since these methods result in a relational expression in which the estimated position error is improved, any of these methods can be used.

[0048] Next, the processes of steps S31 and S32 (FIG. 4) are performed in time series within a predetermined time range, and the reception intensity and the EHPE value (ehpe) are acquired in time series (step S44). After the elapse of a predetermined time, it is determined whether db1_thr < db1, div < div_thr, and ehpe < ehpe_thr (step S45).

[0049] When db1_thr < db1, div < div_thr, and ehpe < ehpe_thr (Yes in step S45), the reception intensity is reset, and the process from step S31 is repeated. In this case, it means that the position accuracy degradation rate of the satellites in the selected intensity range is low and the accuracy is relatively good. Therefore, it is changed to the reception intensity reset as the control value, and the process from step S31 is repeated. At this time, the traveling state determination processing unit 24 stores in the storage device 27 that it is in the positioning calculation state (State1) along with the time. Also, when the position accuracy degradation rate of the satellites in the selected intensity range is low and the accuracy is relatively good, the position coordinates calculated by the vehicle position correction unit 25 and the speed calculated by the self-position measurement calculation processing unit 23 can be preferentially used as the position information of the railway vehicle 11.

[0050] On the other hand, when db1_thr < db1, div < div_thr, but the number of data where ehpe < ehpe_thr does not exceed a predetermined value (NO in step S45), it means that the quality of the received signals of the satellites in the selected elevation range is low. The reception intensity is controlled (reset) (step S43), and the process from step S44 is repeated. When db1_thr > db1 or div > div_thr, it means that the radio wave reception environment is bad, and the determination of ehpe < ehpe_thr is not performed, and it waits.

[0051] In this way, when resetting the reception intensity, the signal intensity of the satellites and the position accuracy degradation rate of the satellites in the selected intensity range are tried and confirmed for a predetermined period. Therefore, the upper limit value and the lower limit value of the signal intensity can be set with higher accuracy. By controlling the upper limit value and the lower limit value of the signal intensity in this way, it becomes possible to obtain a more accurate positioning signal.

[0052] Incidentally, when db ≤ db_thr in the determination in step S34 (see FIG. 5) and ehpe_thr ≤ ehpe in the determination in step S41 (see FIG. 6), it is considered that the estimated position error will not be improved even if both reception intensity control and elevation angle control are performed. That is, since it is considered that the positioning accuracy is not improved, the positioning method is switched to self-measurement (step S47), and the process transitions to self-measurement processing (step S84) (see FIG. 8). At this time, the traveling state determination processing unit 24 stores in the storage device 27 that it is in the self-measurement processing state (State2) together with the time. Since it is considered that the estimated position error will not be improved even if both reception intensity control and elevation angle control are performed, it becomes possible to preferentially use the position coordinates calculated by the vehicle position correction unit 25 and the speed calculated by the self-measurement calculation processing unit 23 as the position information of the railway vehicle 11.

[0053] On the other hand, when pdop < pdop_thr in the determination in step S35 (FIG. 4) (Yes in step S35), since the reception intensity is sufficiently strong and the estimated position error is small, the control of the satellite elevation angle is not necessary at this time, and the process transitions to branch processing D.

[0054] FIG. 7 is a flowchart of branch processing D. Here, with reference to FIG. 4, an example of the process of switching to self-measurement processing in the invisible region will be described.

[0055] The railway vehicle 11 performs the position measurement of the railway vehicle 11 using the positioning radio signals SX1 to SX4 in the positioning signal calculation processing unit 21 and the position measurement of the railway vehicle 11 based on the output signals from the three-axis sensor unit CSU in the self-positioning calculation processing unit (second positioning unit) 23 in parallel (step S610).

[0056] The self-measurement switching determination unit 26 sequentially acquires the track information of the track L2 on the map and the information of the invisible regions B1 to B2 acquired from the storage device 27 (step S620), and acquires the traveling direction of the railway vehicle 11 obtained by the self-positioning calculation processing unit (second positioning unit) 23 (step S630).

[0057] Next, the self - contained measurement switching determination unit 26 collates the current position of the railway vehicle 11 on the track of the track L2 based on the traveling direction of the railway vehicle 11 and the position measurement of the railway vehicle 11 obtained in step S610 (step S640). Subsequently, the self - contained measurement switching determination unit 26 determines whether the current position of the railway vehicle 11 corresponds to the start point B1 or B2 of the invisible regions B1 to B2 (step S650). For example, if the railway vehicle 11 is going uphill, point B1 is the start point of the invisible regions B1 to B2, and if the railway vehicle 11 is going downhill, point B2 is the start point of the invisible regions B1 to B2. Conversely, if the railway vehicle 11 is going uphill, point B2 is the end point of the invisible regions B1 to B2, and if the railway vehicle 11 is going downhill, point B1 is the end point of the invisible regions B1 to B2.

[0058] When the self - contained measurement switching determination unit 26 determines that the railway vehicle 11 has entered the invisible regions B1 to B2 (Yes in step S650), even if the received signal strength is sufficiently strong and the estimated position error is small, it switches to self - contained measurement (step S47) and shifts to the self - contained measurement process (step S84) (Figure 8). Thereby, it is possible to shift to the self - contained measurement process more accurately before the radio wave deteriorates. At this time, the running state determination processing unit 24 stores in the storage device 27 that it is in the self - contained measurement processing state (State2) along with the time. It becomes possible to preferentially use the position coordinates calculated by the vehicle position correction unit 25 and the speed calculated by the self - contained measurement calculation processing unit 23 as the position information of the railway vehicle 11.

[0059] For example, as in the prior art, when detecting and switching due to a decrease in the reception intensity of radio waves, there may be a case where the position where the decrease occurs enters the invisible regions B1 to B2, and there is a risk that the switching may be delayed. On the other hand, when determining whether the current position of the railway vehicle 11 corresponds to the start point B1 or B2 of the invisible regions B1 to B2, the speed information of the railway vehicle 11 is also used to calculate the time point when the start point B1 or B2 of the invisible regions B1 to B2 is reached, and it is also possible to shift to the self-measurement process in accordance with the time point when the start point B1 or B2 is reached. Thereby, the delay in shifting to the self-measurement process is suppressed. For example, when the railway vehicle 11 is traveling at a high speed in the upward direction at a speed of 200 kilometers per hour or the like, it is also possible to start the shift to the self-measurement process before reaching the start point B1 and make the switching point P1 coincide with the start point B1. Even in a case where the switching is delayed in the prior art, the position measurement can be continuously performed more stably. Further, the positions of the start points B1 or B2 may be set in front of the invisible regions B1 to B2 in accordance with the specified speed of the railway vehicle 11. In this case, it is possible to shift to the self-measurement process without using the speed information.

[0060] On the other hand, when it is determined that the railway vehicle 11 does not enter the invisible regions B1 to B2 (No in step S65), the process transitions to the branch process C, and the process from step S31 (FIG. 4) is repeated. In this case, the measurement mainly using the position measurement information of the railway vehicle 11 using the positioning radio wave signals SX1 to SX4 in the positioning signal calculation processing unit 21 is continued. Thus, when the positioning accuracy in the positioning signal calculation processing unit 21 is high, the position measurement information in the positioning signal calculation processing unit 21 is mainly used, and in a region where the positioning accuracy in the self-positioning calculation processing unit (second positioning unit) 23 is higher than the positioning accuracy in the positioning signal calculation processing unit 21, it is possible to mainly use the position measurement information in the positioning signal calculation processing unit 21.

[0061] FIG. 8 is a flowchart (Part 2) of satellite reception control processing and autonomous measurement switching determination processing. As described above, when the positioning accuracy is not improving, the positioning method is switched to autonomous measurement (step S47), and the process transitions to autonomous measurement processing (step S840). In this case, while receiving positioning signals from satellites etc. in parallel during the transition to autonomous measurement processing, the positioning accuracy is considered to be poor. However, as soon as the situation becomes such as after emerging from a tunnel where the positioning accuracy improves, it is necessary to switch to satellite positioning.

[0062] Therefore, as shown in FIG. 8, in parallel with autonomous positioning, using the acquired positioning signals, the elevation angle and reception intensity of the positioning satellite are acquired, and the calculation and acquisition of the estimated position error are performed (steps S31, S32). Then, based on the azimuth in the traveling direction of the railway vehicle 11 corresponding to the acquired positioning signal, the reception azimuth angle is set (step S33).

[0063] Next, the autonomous measurement switching determination unit 26 determines whether or not the measured reception intensity db is less than the predetermined reception intensity determination threshold db_thr stored in the storage device 27 (step S810). If db_thr < db (No in step S810), it means that the reception intensity is sufficiently strong, the sensitivity is good, and the positioning accuracy is relatively good. In order to determine whether reception intensity control is necessary, it is determined whether or not the measured EHPE value (ehpe) is less than the predetermined EHPE determination threshold ehpe_thr stored in the storage device 27 (step S82).

[0064] When ehpe < ehpe_thr (Yes in step S820), it means that the position accuracy degradation rate is low and the accuracy is relatively good. The self-position measurement switching determination unit 26 outputs a self-position measurement end command to end the self-position measurement and shifts the process to step S31 (see FIG. 4), and starts satellite positioning with the position calculated at the end of the self-position measurement process as the first point of satellite positioning (step S830). At this time, the traveling state determination processing unit 24 stores in the storage device 27 that it is in the self-position measurement processing state (State2) along with the time. Since it is considered that the estimated position error cannot be improved even when both reception intensity control and elevation angle control are performed, it is possible to preferentially use the position coordinates calculated by the vehicle position correction unit 25 and the speed calculated by the self-position measurement calculation processing unit 23 as the position information of the railway vehicle 11.

[0065] On the other hand, when ehpe ≥ ehpe_thr (Yes in step S810), it means that the position accuracy degradation rate is high and the accuracy is relatively poor. The self-position measurement process is continued (step S840), and the speed calculated by the self-position measurement processing unit 23 is used (step S840).

[0066] Similarly, when it is determined that db_thr ≥ db (No in step S820), the reception intensity is weak, the sensitivity is poor, and the positioning accuracy is relatively poor. Therefore, the self-position measurement process is continued (step S840), and the speed calculated by the self-position measurement processing unit 23 is used (step S840).

[0067] In parallel with the processing of steps 31 to S83, the processing of steps 610 to S660 is also performed in parallel. That is, the railway vehicle 11 performs the position positioning of the railway vehicle 11 using the positioning radio signals SX1 to SX4 in the positioning signal calculation processing unit 21 and the position positioning of the railway vehicle 11 based on the output signals from the three-axis sensor unit CSU in the vehicle position correction unit 25 in parallel (step S610). Here, since it is within the invisible regions B1 to B2, the position information by the vehicle position correction unit 25 is mainly used.

[0068] The self-position measurement switching determination unit 26 sequentially acquires the track information of the track L2 on the map and the information of the invisible regions B1 to B2 acquired from the storage device 27 (step S620), and acquires the traveling direction of the railway vehicle 11 obtained by the self-position measurement arithmetic processing unit 23 (step S630).

[0069] Next, the self-position measurement switching determination unit 26 collates the current position of the railway vehicle 11 on the track of the track L2 based on the traveling direction of the railway vehicle 11 and the position measurement of the railway vehicle 11 obtained in step S610 (step S640). Subsequently, the self-position measurement switching determination unit 26 determines whether or not the current position of the railway vehicle 11 corresponds to the end point B1 or B2 of the invisible regions B1 to B2 (step S660). For example, if the railway vehicle 11 is going uphill, the point B2 is the end point of the invisible regions B1 to B2, and if the railway vehicle 11 is going downhill, the point B1 is the end point of the invisible regions B1 to B2.

[0070] When the self-position measurement switching determination unit 26 determines that the railway vehicle 11 has come out of the invisible regions B1 to B2 (No in step S650), it outputs a self-position measurement end command to end the self-position measurement and shifts the process to step S31 (see FIG. 4), and starts satellite positioning with the position calculated at the end of the self-position measurement processing as the first point of the satellite positioning (step S830). Thereby, it is possible to shift to satellite positioning more accurately in accordance with the timing when the radio wave disturbance is eliminated.

[0071] When evaluating radio wave interference and switching, there are cases where the position where the interference is eliminated may be immediately after the invisible regions B1 to B2, and there is a risk that the switching may be delayed. On the other hand, when determining whether the current position of the railway vehicle 11 corresponds to the end point B1 or B2 of the invisible regions B1 to B2, for example, using the speed information of the railway vehicle 11, it is possible to calculate the time point when reaching the end point B1 or B2 of the invisible regions B1 to B2. Thereby, it is also possible to shift to satellite positioning in accordance with the time point of reaching the end point B2. In this way, the delay in shifting to satellite positioning is suppressed. For example, when the railway vehicle 11 is traveling upward at a high speed of 200 kilometers per hour, etc., it is also possible to start the shift to satellite positioning before reaching the end point B2 and make the switching point P2 coincide with the end point B2. Thereby, even in cases where the switching was conventionally delayed, it is possible to continuously perform position measurement more stably. Also, the positions of the end points B1 or B2 may be set in front of the invisible regions B1 to B2 in accordance with the specified speed of the railway vehicle 11. In this case, it is possible to shift to satellite positioning processing without using speed information.

[0072] Also, since the processes of steps 31 to S830 are being performed in parallel, when the states of the positioning radio wave signals SX1 to SX4 are poor, self-positioning is maintained. For this reason, shifting to satellite positioning processing is also suppressed when the states of the positioning radio wave signals SX1 to SX4 are poor.

[0073] Next, while referring to FIG. 9, an example of another branch process D will be described. Here, while referring to FIG. 9, an example of a process of switching to self-positioning processing in the invisible regions B1 to B2 based on the information of the positioning radio wave signals SX1 to SX4 will be described.

[0074] FIG. 9 is a diagram schematically showing the processing environment when detecting the invisible regions B1 to B2 by the positioning radio wave signals SX1 to SX4. The railway vehicle 11 travels on the track of the real-space line L1. Also, the positioning signal calculation processing unit 21 calculates the locus L3 of the traveling vector of the railway vehicle 11 using the positioning radio wave signal R3. The positioning radio wave signal R3 schematically shows the positioning radio wave signals SX1 to SX4.

[0075] Figure 10 is a flowchart of another branch process D. Here, with reference to FIG. 9, an example of a process of switching to self-measurement processing in an invisible region will be described.

[0076] The self-measurement switching determination unit 26 calculates the average value db1 and the variance value dv1 of the time series values obtained by measuring the positioning radio wave signal R3 for a predetermined period (step S910). As described above, the average value db1 decreases in the invisible regions B1 to B2, and the variance value dv1 increases in the region including the front and rear of the invisible regions B1 to B2.

[0077] The road vehicle 11 simultaneously performs the position positioning of the railway vehicle 11 using the positioning radio wave signals SX1 to SX4 in the positioning signal calculation processing unit 21 and the position positioning of the railway vehicle 11 based on the output signal from the three-axis sensor unit CSU in the vehicle position correction unit 25 (step S920). Subsequently, in the positioning signal calculation processing unit 21, the traveling direction of the road vehicle 11 is calculated as the traveling vector L3 based on the positioning radio wave signals SX1 to SX4 (step S930).

[0078] Next, the positioning signal calculation processing unit 21 calculates the change amount r1 per unit time of the traveling vector L3 (step S940).

[0079] The self - measuring switching determination unit 26 determines that it is the starting point B1 of the invisible regions B1 to B2, for example, when r1 > r1_thr (step S950). The progress vector L3 is highly sensitive to the disturbance of the intensities of the positioning radio signals SX1 to SX4, and near the starting point B1 of the invisible regions B1 to B2, the change amount r1 fluctuates more greatly. Thereby, it becomes possible to determine that the starting point B1 has been approached. In this case, the variance value dv1 and the average value db1 of the positioning radio signal R3 may also be used to determine whether the current position of the railway vehicle 11 corresponds to the starting point B1 or B2 of the invisible regions B1 to B2. That is, the determination conditions may be added with db1 ≦ db1_thr and dv1 > dv1_thr. Thereby, when the disturbance of the intensities of the positioning radio signals SX1 to SX4 is small, it is possible to further suppress the mis - determination that it is the starting point B1 of the invisible regions B1 to B2. Thus, even without using the track information of the track L1, it is possible to determine the starting point B1 of the invisible regions B1 to B2. It is also possible to determine the invisible regions B1 to B2 even when there is no map data or when there are buildings not on the map information.

[0080] When the self - measuring switching determination unit 26 determines that the railway vehicle 11 has entered the invisible regions B1 to B2 (Yes in step S950), it switches to self - measuring (step S47) and shifts to the self - measuring process (step S84) (Fig. 11).

[0081] On the other hand, when it is determined that the railway vehicle 11 has not entered the invisible regions B1 to B2 (No in step S950), it transitions to the branch process C and repeats the process from step S31 (Fig. 4). In this case, the measurement is continued mainly using the position - measurement information of the railway vehicle 11 using the positioning radio signals SX1 to SX4 in the positioning signal calculation processing unit 21. Thus, when the positioning accuracy in the positioning signal calculation processing unit 21 is high, the position - measurement information in the positioning signal calculation processing unit 21 is mainly used, and in the region where the positioning accuracy in the vehicle position correction unit 25 is higher than the positioning accuracy in the positioning signal calculation processing unit 21, it is possible to mainly use the position - measurement information in the vehicle position correction unit 25.

[0082] FIG. 11 is a flowchart in the case of using the process shown in FIG. 10. It is different from FIG. 8 in that the method described in FIG. 10 is used for the determination method of the invisible region. Hereinafter, the differences from FIG. 8 will be described.

[0083] The self-position measurement switching determination unit 26 determines, for example, that it is the end point B2 of the invisible regions B1 to B2 when r1 < r1_thr (step S960). The progress vector L3 is highly sensitive to the disturbance of the intensity of the positioning radio signals SX1 to SX4, and near the end point B2 of the invisible regions B1 to B2, the disturbance of the intensity decreases, so the change amount r1 becomes small. Thereby, it becomes possible to determine that the end point B2 has been approached. In this case, the variance value dv1 and the average value db1 of the positioning radio signal R3 may also be used to determine whether the current position of the railway vehicle 11 corresponds to the start point B1 or B2 of the invisible regions B1 to B2. That is, it may be added that the determination conditions are db1 ≧ db1_thr and dv1 < dv1_thr. Thereby, when the disturbance of the intensity of the positioning radio signals SX1 to SX4 is large, it becomes possible to further suppress the misjudgment that it is the end point B2 of the invisible regions B1 to B2. As described above, when the positioning accuracy is in a situation where it does not improve, the positioning method is switched to self-position measurement (step S46), and the process transitions to the self-position measurement process (step S840). In this case, while receiving the positioning signals such as satellites in parallel during the transition to the self-position measurement process, it is considered that the positioning accuracy is poor, but it is necessary to switch to satellite positioning as soon as the situation such as after coming out of a tunnel where the positioning accuracy improves occurs.

[0084] Next, a processing example of switching to the self-position measurement process based on the map data and the information of the positioning radio signals SX1 to SX4 will be described with reference to FIG. 12.

[0085] FIG. 12 is a diagram schematically showing a processing environment in the case of switching to the invisible regions B1 to B based on the map data and the information of the positioning radio signals SX1 to SX4. The railway vehicle 11 travels on the track of the line L1 in the real space. Further, the positioning signal calculation processing unit 21 calculates the locus L3 of the progress vector of the railway vehicle 11 using the positioning radio signal R3. The positioning radio signal R3 schematically shows the positioning radio signals SX1 to SX4.

[0086] FIG. 13 is a flowchart of yet another branch process D. Here, with reference to FIG. 12, an example of a process of switching to self-measurement processing in an invisible region will be described. FIG. 13 is a flowchart corresponding to FIG. 8. The differences from the processing of FIG. 8 will be described below.

[0087] The self-measurement switching determination unit 26 determines whether the current position of the railway vehicle 11 corresponds to the start point B1 or B2 of the invisible regions B1 to B2 by also using the dispersion value dv1 and the average value db1 of the positioning radio wave signal R3 (step S1300). For example, the self-measurement switching determination unit 26 determines whether the current position of the railway vehicle 11 corresponds to the start point B1 or B2 of the invisible regions B1 to B2 by also using the dispersion value dv1 and the average value db1 of the positioning radio wave signal R3. For example, when the determination conditions are db1 ≧ db1_thr and dv1 < dv1_thr, or when the railway vehicle 11 reaches a predetermined position, it is determined that the regions are the invisible regions B1 to B2.

[0088] Thereby, for example, even when an unexpected invisible region that is not stored in the storage device 27, for example, due to a moving object, a building under construction, etc., occurs, it becomes possible to determine that the railway vehicle 11 is within the invisible region.

[0089] FIG. 14 is a flowchart when the process shown in FIG. 13 is used. It is different from FIG. 8 in that the method described in FIG. 13 is used for the determination method of the invisible region. The differences from FIG. 8 will be described below.

[0090] The self - contained measurement switching determination unit 26 determines whether the current position of the railway vehicle 11 corresponds to the end point B1 or B2 of the invisible regions B1 to B2 by also using the variance value dv1 and the average value db1 of the positioning radio wave signal R3 (step S1400). For example, when the determination condition is db1 ≥ db1_thr and dv1 < dv1_thr, or when the railway vehicle 11 reaches a predetermined position, the self - contained measurement switching determination unit 26 determines that it is the end point B1 or B2 of the invisible regions B1 to B2. Thereby, even when, for example, another invisible region occurs due to a building not stored in the storage device 27, a building under construction, etc., it is possible to determine that the railway vehicle 11 has come out of the invisible region.

[0091] Next, the details of the satellite reception control will be described. FIG. 15 is a processing flowchart of the received satellite control process in the satellite reception control unit 22. The satellite reception control unit 22 executes a function of selecting artificial satellites used for position detection according to the positioning environment.

[0092] When the antenna 13 for receiving the positioning signal (hereinafter may be simply referred to as the antenna 13) is inside the railway vehicle 11, in particular, for the traveling direction, the positioning signals from satellites in the reverse direction or satellites existing in the side direction are likely to be received after reflection or diffraction, which will immediately affect the measurement accuracy. Therefore, the satellite reception control unit 22 performs the received satellite control process to maintain the measurement accuracy.

[0093] As shown in FIG. 15, first, the satellite reception control unit 22 uses the acquired positioning signal to acquire the positioning satellite elevation angle and the reception intensity (step S61). Next, the satellite reception control unit 22 acquires the satellite almanac information and the satellite ephemeris information from the artificial satellites that can receive them, and acquires the orbit information of the artificial satellites 12 - 1 to 12 - 4 (step S62).

[0094] FIG. 16 is an explanatory diagram of the reception state of positioning information. FIG. 16(a) is an image diagram of satellite orbit information. In FIG. 16(a), the antenna 13 of the railway vehicle 11 is arranged at the center of the circle. In FIG. 16(a), the ○ mark represents the current position of the artificial satellite, and the curve passing through the current position of the artificial satellite represents the satellite orbit information of each artificial satellite.

[0095] In a situation like that in FIG. 16(a), the actually receivable range at the antenna 13 of the railway vehicle 11 varies depending on the arrangement position of the antenna 13 and the traveling position of the railway vehicle 11. For example, as shown in FIG. 16(b), the satellite reception control unit 22 sets a reception effective area AE and a reception ineffective area AN, and based on the traveling direction DR of the railway vehicle 11, the reception azimuth angle is set to be, for example, 135 degrees in the clockwise direction and the counterclockwise direction with respect to the traveling direction DR. FIG. 17 is a diagram showing an example of setting the reception effective area AE and the reception ineffective area AN in the case of speed measurement in the positioning signal speed calculation unit (second measurement unit) 29. In the case of speed measurement in the positioning signal speed calculation unit (second measurement unit) 29, since speed measurement is performed by Doppler, the reception effective area AE is more restricted in the traveling direction DR. In this case, the reception azimuth angle is set to be, for example, 45 degrees in the clockwise direction and the counterclockwise direction (step S63).

[0096] Furthermore, as shown in FIG. 16(c), the satellite reception control unit 22 sets a satellite arrangement determination area AD for determining the artificial satellite arrangement position for selecting the artificial satellite after traveling so as to be 90 degrees in the clockwise direction and the counterclockwise direction with respect to the traveling direction DR of the railway vehicle 11 for the reception effective area AE corresponding to the set reception azimuth angle, and continuously performs the process of specifying the artificial satellite to be selected next time (step S64).

[0097] Here, the artificial satellite selection process in the satellite reception control unit 22 will be described in detail. FIG. 18 is an explanatory diagram of the artificial satellite selection process. As shown in FIG. 18, the traveling direction of the railway vehicle 11 is forward in the direction perpendicular to the plane of the paper. Then, the satellite reception control unit 22 selects, as valid artificial satellites 12E, artificial satellites belonging to a set reception intensity (a range specified by the reception intensity upper limit value and the reception intensity lower limit value) from among the artificial satellites located in the reception effective area AE.

[0098] Conversely, artificial satellites 12N1, 12N21, and 12N2 that do not belong to the set reception intensity range are determined to be invalid and excluded from the selection. More specifically, the artificial satellites selected as valid artificial satellites 12E are satellites that can directly receive the positioning signal via the antenna 13 among the artificial satellites located in the reception effective area AE.

[0099] On the other hand, the invalid artificial satellite 12N1 is a satellite that cannot receive the positioning signal because the positioning signal cannot reach it due to obstacles BR such as buildings and mountains.

[0100] Also, the invalid artificial satellite 12N21 is a satellite in which the positioning signal is reflected by obstacles BR such as buildings and mountains and reaches the antenna 13, resulting in a time delay and a decrease in reception intensity, thereby reducing the positioning accuracy.

[0101] Also, the invalid artificial satellite 12N22 is a satellite in which the positioning signal diffracts due to obstacles BR such as buildings and mountains and reaches the antenna 13, resulting in a time delay and a decrease in reception intensity, thereby reducing the positioning accuracy.

[0102] FIG. 19 is an explanatory diagram of the elevation angle control in the satellite reception control unit 22. As shown in FIG. 19(a), the satellite reception control unit 22 controls the elevation angle EL so as to include all the valid artificial satellites 12E selected by the above-described artificial satellite selection process and not to include the invalid artificial satellites 12N (= artificial satellite 12N21 and artificial satellite 12N22).

[0103] As a result, the effective elevation angle range AEL becomes as shown in Fig. 19(b). Further, as shown in Fig. 16, satellites located in the reception effective area AE are identified, and the corresponding positioning signals are processed. As a result, it becomes possible to maintain the positioning accuracy at a desired value or higher.

[0104] In this case, the satellite reception control unit 22 periodically acquires the traveling direction of the railway vehicle 11 from the reception azimuth angle for a certain period (e.g., 1 second), and obtains the averaged azimuth angle as the traveling direction angle. Satellites existing in this traveling direction angle may be selected from the satellite orbit information.

[0105] Furthermore, when the azimuth angle of the traveling direction changes significantly (e.g., 10°) due to a curve or a route change, etc., the traveling direction angle may be acquired as needed, and the satellites may be selected from the satellite orbit information. By these, it becomes possible to select only the positioning signals that can improve the position detection accuracy.

[0106] Next, the functions of the self - contained measurement calculation processing unit 23 and the running state determination processing unit 24 will be described in detail. The self - contained measurement calculation processing unit 23 has a function of performing initial value calculation processing for calibration based on the acceleration information, gyro information, and geomagnetic information output by the three - axis sensor unit CSU, a function of performing correction calculation processing for the cumulative error of the three - axis sensor values, and a function of calculating the speed information of the railway vehicle 11 based on the corrected calculated values and the three - axis sensor values. The running state determination processing unit 24 has a function of selecting and processing the running information of the railway vehicle 11 estimated to be within the error tolerance range based on the speed information of the railway vehicle 11 obtained from the satellite reception information and the speed information calculated by the self - contained measurement calculation processing unit 23, and a function of determining stop and running based on the speed information of the railway vehicle 11.

[0107] Fig. 20 is a processing flowchart of the self - contained measurement calculation processing unit 23 and the running state determination processing unit 24. First, the self - contained measurement calculation processing unit 23 acquires the acceleration information, gyro information, and geomagnetic information output by the three - axis sensor unit CSU (step S71).

[0108] Next, the self-supporting measurement operation processing unit 23 performs initial value operation processing based on the acquired acceleration information, gyro information, and geomagnetic information (step S72). This initial value operation processing is preferably basically performed while the railway vehicle 11 is stopped. Here, the reason for performing the initial value operation processing while the railway vehicle 11 is stopped is that performing the initial value operation processing during movement not only affects the measured values but also makes it difficult to initialize the cumulative error.

[0109] In the following description, in order to obtain more accurate measurement values and initialize the cumulative error, it will be described as performing the initial value operation processing while stopped. While the railway vehicle 11 is stopped, the respective values of the acceleration information, gyro information, and geomagnetic information output by the three-axis sensor unit CSU are integrated and averaged, and the obtained integrated average value is acquired as the offset value of each three-axis sensor and used as the initial value operation processing.

[0110] And the function of correcting and calculating the cumulative error for each value of the acceleration information, gyro information, and geomagnetic information output by the three-axis sensor unit CSU can offset the cumulative error by applying it to each value of the three-axis sensor that has acquired this offset value.

[0111] In addition, the initial value operation processing is not only before the start of running of the railway vehicle 11, but also when the railway vehicle 11 stops at a station or the like. When the predetermined set time has elapsed and the stopped state continues, by performing the same initial value operation processing, it is possible to re-acquire the offset amount and offset the cumulative error at any time, thereby reducing the cumulative error.

[0112] The cumulative error esn of the three-axis sensor values output by the three-axis sensor unit CSU is monitored (step S73), and the output values of the three-axis sensor values are corrected to calculate the corrected three-axis sensor values (step S74).

[0113] Next, the self - contained measurement calculation processing unit 23 calculates the speed of the railway vehicle 11 from the obtained corrected three - axis sensor values (step S75). Here, the speed calculation of the railway vehicle 11 is performed by integrating the acceleration values, which are the outputs of the three - axis acceleration sensors output by the three - axis sensor unit CSU, at the time intervals when the values are obtained, and calculates the speed information of the railway vehicle 11. Each piece of information is output in time series as self - contained positioning data DS. On the other hand, the running state determination processing unit 24 acquires the speed information of the railway vehicle 11 obtained from the satellite reception information (step S76).

[0114] Next, the running state determination processing unit 24 compares the cumulative error tolerance value esn_thr of the three - axis sensor with the monitored cumulative error esn, and determines whether the cumulative error esn is less than the cumulative error tolerance value esn_thr (step S77).

[0115] More specifically, it determines whether it is a situation where the railway vehicle 11 has not been running continuously for a predetermined time or more since the previous stop of the railway vehicle 11 and the cumulative error of the three - axis sensor is considered to be within the allowable range.

[0116] In the determination of step S77, when the cumulative error esn is less than the cumulative error tolerance value esn_thr, that is, when esn < esn_thr (step S77; Yes), the running state determination processing unit 24 considers that the reliability of the speed information of the railway vehicle 11 corresponding to the output of the three - axis acceleration sensor output by the three - axis sensor unit CSU is high. Therefore, it selects the speed information spd of the railway vehicle 11 corresponding to the output of the three - axis acceleration sensor (step S78), and based on the speed information spd of the railway vehicle 11 corresponding to the output of the three - axis acceleration sensor and the predetermined railway vehicle 11 speed determination value spd_thr stored in the storage device 27, determines whether the speed information spd of the railway vehicle 11 < the railway vehicle 11 speed determination value spd_thr (step S80). Here, if spd < spd_thr, the railway vehicle 11 is in a stopped state, and if spd ≧ spd_thr, the railway vehicle 11 is in a running state.

[0117] In the determination of step S80, if it is determined that spd < spd_thr (step S80; Yes), since the railway vehicle 11 is in a stopped state, the running state determination processing unit 24 outputs that the railway vehicle 11 is stopped and the speed information of the railway vehicle 11 corresponding to the output of the three-axis acceleration sensor output by the three-axis sensor unit CSU, and ends the processing (step S81).

[0118] In the determination of step S80, if it is determined that spd ≥ spd_thr (step S80; No), since the railway vehicle 11 is in a running state, the running state determination processing unit 24 outputs that the railway vehicle 11 is running and the speed information of the railway vehicle 11 corresponding to the output of the three-axis acceleration sensor output by the three-axis sensor unit CSU, and ends the processing (step S82).

[0119] On the other hand, in the determination of step S77, if the cumulative error esn is greater than or equal to the cumulative error tolerance value esn_thr, that is, if esn ≥ esn_thr (step S77; No), it is the continuous running state of the railway vehicle 11, and the reliability of the speed information of the railway vehicle 11 corresponding to the output of the three-axis acceleration sensor output by the three-axis sensor unit CSU is low. If the state stored in the storage device 27 is Stat1, it is considered that the reliability of the speed information of the railway vehicle 11 corresponding to the satellite information is high. Therefore, the speed information spd of the railway vehicle 11 corresponding to the satellite information is selected (step S79). If the state is Stat2, the processing waits until the state changes to Stat1. In addition, if the state stored in the storage device 27 is Stat1, the running state determination processing unit 24 can preferentially use the speed calculated by the positioning signal speed calculation unit 29.

[0120] Based on the speed information spd of the railway vehicle 11 corresponding to the received data from the artificial satellite and a predetermined railway vehicle 11 speed determination value spd_thr stored in the storage device 27, it is determined whether the speed information spd of the railway vehicle 11 < the railway vehicle 11 speed determination value spd_thr (step S80). Here, if spd < spd_thr, the railway vehicle 11 is determined to be in a stopped state, and if spd ≧ spd_thr, the railway vehicle 11 is determined to be in a running state.

[0121] In the determination of step S80, if it is determined that spd < spd_thr (step S80; Yes), since the railway vehicle 11 is in a stopped state, it is output that the railway vehicle 11 has stopped and the speed information of the railway vehicle 11 corresponding to the received data from the artificial satellite, and the process ends (step S81).

[0122] In the determination of step S80, if it is determined that spd ≧ spd_thr (step S40; No), since the railway vehicle 11 is in a running state, it is output that the railway vehicle 11 is running and the speed information of the railway vehicle 11 corresponding to the received data from the artificial satellite, and the process ends (step S82).

[0123] Figure 21 is a processing flowchart of the vehicle position correction unit 25. The vehicle position correction unit 25 acquires the estimated position error (EHPE and PDOP) pos calculated by the satellite reception control unit 22 (step S91).

[0124] Subsequently, the vehicle position correction unit 25 acquires a predetermined position error tolerance value pos_thr stored in the storage device 27, compares the acquired estimated position error pos with the position error tolerance value pos_thr, and determines whether the estimated position error pos < the position error tolerance value pos_thr, that is, whether the position detection accuracy is relatively good (step S92).

[0125] In the determination in step S92, when the estimated position error pos < the position error tolerance value pos_thr (step S92; Yes), since the position detection accuracy is considered to be relatively good, the running state determination processing unit 24 acquires the stop information or running information of the railway vehicle 11 (step S93).

[0126] Next, the vehicle position correction unit 25 determines whether the railway vehicle 11 is in a stopped state or a running state (step S94).

[0127] In the determination in step S94, when the estimated position error pos < the position error tolerance value pos_thr and the railway vehicle 11 is in a stopped state (step S94; Yes), the triaxial sensor unit CSU initializes the triaxial sensor values (step S95), and the vehicle position correction unit 25 returns the process to step S91 again.

[0128] On the other hand, in the determination in step S94, when the estimated position error pos ≥ the position error tolerance value pos_thr (step S94; No), since the position detection accuracy is considered to be relatively poor, the speed information output by the running state determination processing unit 24 is acquired (step S96).

[0129] The self-position measurement calculation processing unit 23 calculates the speed of the railway vehicle 11 from the obtained corrected triaxial sensor values (step S75). Here, the speed calculation of the railway vehicle 11 is calculated as the speed information of the railway vehicle 11 by performing integration processing at the time interval when the value of the acceleration, which is the output of the triaxial acceleration sensor output by the triaxial sensor unit CSU, is acquired, and each information is output in time series as the self-positioning data DS.

[0130] Subsequently, the vehicle position correction unit 25, the self-position measurement calculation processing unit 23 performs azimuth angle calculation (step S97), and the vehicle position correction unit 25 acquires the value. Subsequently, the self-position measurement calculation processing unit 23 performs calculation of the running vector in the three-axis direction (step S98), and the vehicle position correction unit 25 acquires the value.

[0131] Next, when the state is Stat1, the vehicle position correction unit 25 acquires position information (position coordinates) including latitude information and longitude information from the positioning signal calculation processing unit 21, and specifies the current position of the railway vehicle 11 (step S99). If the state is Stat2, the vehicle position correction unit 25 waits for the process of specifying the current position until the state changes to Stat1.

[0132] Then, the vehicle position correction unit 25 obtains the magnitude of the traveling vector in the azimuth direction from the speed information according to the positioning time interval by the received radio wave from the artificial satellite, and performs a cumulative calculation, thereby performing a correction calculation of the current position of the railway vehicle 11 (step S100).

[0133] As described above, according to the first embodiment, the traveling position of the railway vehicle 11 can be surely acquired, and even in a situation where satellite information such as in a tunnel cannot be obtained, a switch to self-positioning with less delay can be made, and more accurate traveling position data can be provided. Also, the traveling position of the railway vehicle 11 can be surely acquired, and even in the speed measurement of the railway vehicle 11 in a situation where satellite information such as in a tunnel cannot be obtained, a switch to speed measurement in self-positioning with less delay can be made, and more accurate speed data can be provided.

[0134] (Second Embodiment) The second embodiment predicts the route of the railway vehicle 11, determines whether the railway vehicle 11 is traveling in a straight section or a curved section, and further compares it with the traveling section information of the railway vehicle 11 stored in advance, thereby providing information for performing appropriate traveling based on whether the actual traveling state of the railway vehicle 11 is suitable for the actual traveling section. This is different from the first embodiment. Hereinafter, the differences from the first embodiment will be described.

[0135] FIG. 22 is a functional configuration block diagram of the reception calculation processing device according to the second embodiment. As shown in FIG. 22, in addition to the configuration of the first embodiment shown in FIG. 2, it is different from the first embodiment in that it includes a vehicle route prediction calculation unit 30 that predicts the actual route (traveling position in a predetermined traveling section) of the railway vehicle 11.

[0136] Here, the operation of the vehicle route prediction calculation unit 30 will be described. FIG. 23 is a processing flowchart (Part 1) of the vehicle route prediction calculation unit. The vehicle route prediction calculation unit 30 acquires and stores position information (position coordinates) including latitude information and longitude information output by the positioning signal calculation processing unit 21 (step S101).

[0137] Subsequently, the vehicle route prediction calculation unit 30 performs an averaging operation on the position information based on the averaging target time previously stored in the storage device 27, and calculates the average position of the railway vehicle 11 for each averaging target time (step S102). Then, the vehicle route prediction calculation unit 30 acquires the traveling direction angle (azimuth of the traveling direction of the railway vehicle 11) of the railway vehicle 11 based on the obtained averaged position information (step S103). Further, the vehicle route prediction calculation unit 30 calculates the attitude angle (for example, cant) of the railway vehicle 11 based on the acceleration information, gyro information, and geomagnetic information output by the three-axis sensor unit CSU (step S104).

[0138] Next, the vehicle route prediction calculation unit 30 acquires the stop / travel state and speed information of the railway vehicle 11 output by the travel state determination processing unit 24 (step S105). Subsequently, the vehicle route prediction calculation unit 30 calculates and stores the traveling direction vector of the railway vehicle 11 (step S106).

[0139] Furthermore, the vehicle route prediction calculation unit 30 performs a traveling direction vector averaging operation to obtain a vector azimuth angle shp, which is the average value of the traveling direction vectors for each predetermined vector calculation target time previously stored in the storage device 27 for the stored traveling direction vector of the railway vehicle 11 (step S107).

[0140] FIG. 24 is a processing flowchart (Part 2) of the vehicle route prediction calculation unit. Subsequently, the vehicle route prediction calculation unit 30 calculates the vector azimuth angle shp (step S111). Next, the vehicle route prediction calculation unit 30 determines whether the current running section of the railway vehicle 11 is a straight section or a curved section based on the speed information of the railway vehicle 11 and the linear determination value shp_thr for determining a straight section or a curved section previously stored in the storage device 27 (step S112).

[0141] That is, it is determined whether the vector azimuth angle shp is less than the linear determination value shp_thr. In the determination of step S112, if shp < shp_thr (step S112; Yes), since the current train running section is a straight section, the vehicle route prediction calculation unit 30 outputs a straight section determination (step S113).

[0142] Subsequently, the vehicle route prediction calculation unit 30 acquires the stop / running state and speed information of the current railway vehicle 11 output by the running state determination processing unit 24 (step S114). Furthermore, the vehicle route prediction calculation unit 30 specifies and acquires the running position and running section of the current railway vehicle 11 based on the running history up to that point and the running section database storing the shape and distance information of the running route for specifying the running section previously stored in the storage device 27 (step S115).

[0143] Next, the speed limit data xspd_thr1 at the specified running position and running section of the railway vehicle 11 is read from the storage device 27, compared with the speed spd of the railway vehicle 11, and it is determined whether the railway vehicle 11 is exceeding the speed (step S116).

[0144] In the determination of step S116, if pd < xspd_thr1 (step S116; No), it is determined that the railway vehicle 11 is running within the speed limit range, so an output of within the speed limit is made and the process ends (step S117).

[0145] In the determination of step S116, if spd ≧ xspd_thr1 (step S116; Yes), it is determined that the railway vehicle 11 is traveling at a speed exceeding the speed limit. Therefore, the determination output of the speed limit exceeding and the current speed are output, and the process ends (step S118).

[0146] Figure 25 is a processing flowchart (part 3) of the vehicle route prediction calculation unit. In the determination of step S112, if shp ≧ shp_thr (step S112; No), since the current train running section is a curve section, as shown in Figure 25, the vehicle route prediction calculation unit 30 outputs a curve section determination output (step S121).

[0147] Subsequently, the vehicle route prediction calculation unit 30 calculates the curve radius (radius of curvature) (step S122), and acquires the cant amount corresponding to the calculated curve radius from a database representing the correspondence between the radius of curvature and the cant amount according to the design criteria previously stored in the storage device 27 (step S123).

[0148] Furthermore, the vehicle route prediction calculation unit 30 specifies and acquires the running position and running section of the current railway vehicle 11 based on the running history up to that point and the running section database storing the shape and distance information of the running route for specifying the running section previously stored in the storage device 27 (step S124).

[0149] Subsequently, the vehicle route prediction calculation unit 30 acquires the stop / travel state and speed information of the current railway vehicle 11 output by the travel state determination processing unit 24 (step S125). Next, the speed limit data xspd_thr2 in the radius of curvature and the cant amount according to the design criteria in the running section, which is the running position and curve section of the specified railway vehicle 11, is read from the storage device 27, compared with the speed spd of the railway vehicle 11, and it is determined whether the railway vehicle 11 is exceeding the speed (step S126).

[0150] In the determination of step S126, if pd < xspd_thr2 (step S126; No), since it is determined that the railway vehicle 11 is traveling within the speed limit range, an output for determination within the speed limit is performed and the process ends (step S127).

[0151] In the determination of step S126, if pd ≥ xspd_thr2 (step S126; Yes), since it is determined that the railway vehicle 11 is traveling at a speed exceeding the speed limit, an output for determination of speed limit exceed and the current speed are output and the process ends (step S128).

[0152] As described above, according to the second embodiment, by acquiring the traveling position of the railway vehicle 11 and predicting the route of the railway vehicle 11 from the acquired data, it is possible to provide data that can be used for setting the forward detection range, route prediction, detection of the traveling position, detection of speed exceed, etc. In addition, it enables the creation of a traveling route map and can be expanded to traveling support and support for creating railway facility information.

[0153] (Modification example of the second embodiment) In the second embodiment, it was the case when outputting speed exceed information, but it can also be used for setting the range of the detection area when detecting an obstacle ahead by a camera or the like.

[0154] That is, the detection area of a camera or the like is usually the area of the structure limit on the track or the vehicle limit of the railway vehicle 11 in the case of a railway. However, when it is desired to permanently or temporarily expand the detection area of a station, a level crossing, etc. due to reconstruction, temporary construction, etc., since the position of the section where the railway vehicle 11 is currently traveling can be measured, if the detection target positions of a station, a level crossing, etc. are recorded in the database of the traveling section, the detection area can be expanded from a certain distance in front.

[0155] In the above description, in the three-axis sensor unit CSU, a configuration including a three-axis acceleration sensor, a three-axis gyro sensor, and a three-axis geomagnetic sensor has been described. However, it may be configured to include at least one of the at least one of the three-axis acceleration sensor or the three-axis gyro sensor.

[0156] As described above, according to the apparatus and method of each embodiment, depending on the situation of the positioning signal from a geostationary satellite or the like, the reception elevation angle, reception intensity, and satellite selection are controlled, and by performing the switching determination of the self-position measurement process, it is possible to detect the position of the railway vehicle 11 even in a situation with a poor reception environment.

[0157] As a result, it is possible to achieve the required accuracy with higher precision (for example, ±1 m), compared to the conventional measurement accuracy of up to ±10 m due to problems such as multipath in the railway line environment.

[0158] Also, it is possible to easily grasp the running position even in areas where satellite reception is impossible, such as under elevated structures like tunnels and on-bridge stations, or in underground sections. Furthermore, by acquiring the running position of the railway vehicle 11 and predicting the route of the railway vehicle 11 from the acquired data, it can be used for setting the forward detection range, route prediction, detection of the running position, detection of speed overrun, etc. Furthermore, it enables the creation of a running route map and can be expanded for running support and support for creating railway facility information.

[0159] The running position detection device for railways of this embodiment has a hardware configuration using a normal computer equipped with a control device such as an MPU, a storage device such as a ROM and a RAM, an external storage device such as an HDD and a CD drive device, a display device for displaying various information, and an input device for inputting various information.

[0160] The program executed by the running position detection device for railways of this embodiment is provided by being recorded on a computer-readable recording medium such as a semiconductor storage device like a CD-ROM and a USB memory device, or a DVD (Digital Versatile Disk) in an installable format or an executable format file.

[0161] Further, the program executed by the railway running position detection device of the present embodiment may be stored on a computer connected to a network such as the Internet and provided by allowing it to be downloaded via the network. Also, the program executed by the railway running position detection device of the present embodiment may be configured to be provided or distributed via a network such as the Internet. Also, the program of the railway running position detection device of the present embodiment may be configured to be provided by being pre - incorporated into a ROM or the like.

[0162] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Explanation of Reference Numerals

[0163] 10: Running position detection system, 11: Railway vehicle, 12 - 1 to 12 - 4: Artificial satellites, 13: Antenna device, 14: External device, 15: Reception arithmetic processing device, 21: Positioning signal arithmetic processing unit, 22: Satellite reception control unit, 23: Self - positioning arithmetic processing unit, 24: Running state determination processing unit, 25: Vehicle position correction unit, 26: Self - measurement switching determination unit, 27: Storage device, 28: Communication connection device, 29: Positioning signal speed processing unit, 30: Vehicle route prediction arithmetic unit, AD: Satellite arrangement determination area, AE: Reception effective area, AEL: Elevation angle range, AN: Reception invalid area, CSU: 3 - axis sensor unit, DG: Positioning data group, DR: Travel direction, DS: Self - positioning data group, EL: Elevation angle.

Claims

1. A position measuring device that measures the position of a vehicle, a first positioning unit that receives a positioning signal from an artificial satellite and locates a first position of the vehicle; a second positioning unit that measures a second position of the vehicle based on an output of a standalone positioning sensor; a second measurement unit that receives a signal from an artificial satellite and measures a second speed of the vehicle; a determination unit that uses information on the first position and the second speed to calculate a first time point at which the position of the vehicle coincides with a start point of an invisible area where reception interference of the positioning signal occurs, and starts a transition of the position of the vehicle from the first position to the second position based on the first time point before the vehicle enters the invisible area, The determination unit is capable of determining that the starting point of the invisible area has been approached using at least one of an estimated horizontal positioning accuracy, a rate of decrease in position accuracy, and a statistic indicating a change in reception strength over time.

2. a first measurement unit that measures a first speed of the vehicle based on an output of a standalone positioning sensor; 2. The positioning device of claim 1, wherein the discrimination unit uses information on the second position and the first speed to calculate a second point in time at which the position of the vehicle coincides with the end point of the invisible area, and starts transitioning the position of the vehicle from the second position to the first position based on the second point in time before the vehicle leaves the invisible area.

3. a reception azimuth angle setting unit that sets a reception azimuth angle based on a traveling direction of the vehicle and a reception state of the positioning signal from an artificial satellite; a satellite selection unit that selects the artificial satellite to be positioned within the set range of the reception azimuth angle; Further comprising: The positioning device according to claim 1 , wherein the first positioning unit receives the positioning signal from the selected artificial satellite.

4. an elevation angle setting unit that sets an elevation angle range for limiting the artificial satellites to be positioned based on a time delay or a received signal strength of the positioning signal among the artificial satellites located within the range of the reception azimuth angle; The positioning device according to claim 3 .

5. 5. The positioning device according to claim 1, wherein the self-contained positioning sensor comprises at least one of a three-axis acceleration sensor, a three-axis gyro sensor, and a three-axis geomagnetic sensor.

6. the vehicle is a rail vehicle, 2. The positioning device according to claim 1, wherein the discrimination unit determines the second position as the position of the vehicle before the position on the track on which the vehicle is traveling reaches the starting point determined based on either a tunnel, a station building, a depot, or an underground section.

7. 4. The position measurement device according to claim 3, wherein the vehicle is a railroad vehicle, and the determining unit is capable of determining that the vehicle has approached the starting point based on an average value and a variance value of the positioning signal.

8. the vehicle is a rail vehicle, The self-contained positioning sensor includes a three-axis gyro sensor, a vehicle course prediction unit that calculates a direction of travel and an attitude angle of the railway vehicle based on the received positioning signal and an output of the three-axis gyro sensor, and calculates a direction of travel vector of the railway vehicle within a set time period to determine whether the railway vehicle is traveling on a straight section or a curved section; a curvature radius calculation unit that calculates a curvature radius of the curved section when it is determined that the railroad vehicle is traveling on the curved section; A storage device that stores a radius of curvature and an amount of cant in accordance with a design standard in advance; a prediction unit that predicts a course of the railway vehicle based on the attitude angle, the traveling direction vector, and a radius of curvature and an amount of cant that conform to the design criteria and correspond to a traveling position of the railway vehicle that are read from the storage device; The positioning device according to claim 1 , further comprising:

9. The positioning device according to claim 2 , wherein the determination unit determines the first speed measured by the first measurement unit as the speed of the vehicle when the position of the vehicle is within a range from the start point to the end point.

10. The positioning device according to claim 9 , wherein the determination unit determines the second speed measured by the second measurement unit as the speed of the vehicle when the position of the vehicle is outside the range from the start point to the end point.

11. a first positioning unit that receives a positioning signal from an artificial satellite and locates a first position of the vehicle; a first measurement unit that measures a first speed of the vehicle based on an output of a standalone positioning sensor; a second measurement unit that receives a signal from an artificial satellite and measures a second speed of the vehicle; a determination unit that uses information on the first position and the second speed to calculate a time when the position of the vehicle coincides with a start point of an invisible area where reception interference of the positioning signal occurs, and starts a transition to set the first speed measured by the first measurement unit as the speed of the vehicle based on the time before the vehicle enters the invisible area; Equipped with A speed measuring device, wherein the discrimination unit is capable of discriminating that the starting point of the invisible area has been approached using at least one of a statistical quantity indicating an estimated horizontal positioning accuracy, a rate of deterioration in position accuracy, and a change in reception strength over time.

12. A positioning method for determining a position of a vehicle, comprising: a first positioning step of receiving a positioning signal from an artificial satellite and determining a first position of the vehicle; a second positioning step of determining a second position of the vehicle based on an output of a stand-alone positioning sensor; a second measuring step of receiving a signal from a satellite and measuring a second speed of the vehicle; a determining step of calculating a time when the position of the vehicle coincides with a start point of an invisible area where reception failure of the positioning signal occurs, using information on the first position and the second speed, and starting a transition of the position of the vehicle from the first position to the second position based on the time before the vehicle enters the invisible area; Equipped with A positioning method in which the discrimination process is capable of discerning the approach to the starting point of the invisible area by using at least one of statistics indicating the estimated horizontal positioning accuracy, the rate of deterioration of position accuracy, and the change in reception strength over time.

Images