An astronomical / geomagnetic combined orientation method

Abstract

The present invention relates to an astronomical / geomagnetic combined orientation method, belonging to the technical field of astronomical / geomagnetic orientation. In the present invention, a geomagnetic module is arranged inside a total station, and the geomagnetic module arranged inside the total station is used for initial rough orientation; then, according to the rough orientation result, the total station is driven to point to any selected star, so that the selected star is within the field of view of the total station telescope, and the star point pixel coordinates of the selected star within the field of view of the total station telescope are obtained by using the camera of the total station; then, according to the obtained star point pixel coordinates of the arbitrary star, the horizontal angle and altitude angle corresponding to the center of the crosshair of the total station telescope, and the theoretical azimuth angle and altitude angle of the arbitrary star, the observed azimuth angle and altitude angle of the arbitrary star are calculated; finally, combined orientation is carried out according to the obtained observed azimuth angles and altitude angles of each arbitrary star. The present invention does not require manual participation, effectively improves the automation degree and observation efficiency of orientation measurement, and can realize the complementary advantages of astronomical / geomagnetic orientation.

Description

Technical Field

[0001] The present invention relates to an astronomical / geomagnetic combined orientation method, belonging to the technical field of astronomical / geomagnetic orientation. Background Art

[0002] Orientation is a technology for determining the direction of a spatial vector in a reference coordinate system, which has important applications in fields such as astronomical geodetic surveying, engineering surveying, mine surveying, and underground drilling. Commonly used orientation means mainly include astronomical orientation, geomagnetic orientation, inertial orientation, GPS orientation, etc. Among them, astronomical orientation has the highest accuracy and is usually used as an absolute azimuth reference to calibrate the orientation results of geomagnetism, inertia, etc.

[0003] Astronomical orientation mainly relies on observing the sun during the day and on characteristic celestial bodies such as the North Star, planets, and moon at night. Some scholars have also proposed using any star to achieve astronomical orientation, but these methods all have the following single or multiple problems that are difficult to solve: 1) Observers need to have professional knowledge of star recognition and star use to correctly identify characteristic stars such as the North Star. However, there are numerous stars on a clear night, and it is very easy to make misidentifications in unfamiliar areas, with blocked views, or in cloudy weather; 2) The observation of any star relies on manual star search and aiming, with low automation and poor reliability; 3) In order to improve the success rate of identifying any star, it is necessary to perform tracking observations on each star for 1-2 minutes to make the any star move a sufficiently long arc segment to ensure the accuracy of the extrapolated position of the any star, which also results in relatively low observation efficiency.

[0004] Geomagnetic orientation is a fast and convenient orientation means, but it also has the following disadvantages that are difficult to overcome: 1) In unfamiliar areas in the wild, affected by environmental factors such as electromagnetic interference, the accuracy of geomagnetic orientation is relatively low, usually only 0.5°; 2) The number of geomagnetic stations in China is limited, the resolution of the geomagnetic field model is limited, and the geomagnetic field has the characteristic of time variation. Therefore, the magnetic declination provided usually has systematic errors and needs to be calibrated before engineering applications.

[0005] Therefore, some people have proposed combining geomagnetic orientation and astronomical measurement. For example, the paper named "Application of Geomagnetic Fast Orientation in the Automation of Astronomical Measurement" (authors Ye Kai, Zhang Chao, Shi Chunlin, etc.) proposed a scheme for combining the two methods. However, this scheme only uses geomagnetic orientation to assist subsequent astronomical measurement. Due to the systematic errors existing in geomagnetic orientation, the accuracy of the orientation result cannot be guaranteed, thus affecting the accuracy of subsequent astronomical measurement. Summary of the Invention

[0006] The purpose of the present invention is to provide an astronomical / geomagnetic combined orientation method to solve the problems of low efficiency, low automation, and low accuracy existing in the current astronomical orientation and geomagnetic orientation processes.

[0007] The present invention provides an astronomical / geomagnetic combined orientation method to solve the above technical problems. The method includes the following steps:

[0008] 1) Use the geomagnetic module installed in the total station for initial orientation to obtain the initial heading angle of the total station and the geomagnetic approximate orientation;

[0009] 2) Obtain an arbitrary star catalog, which includes the theoretical azimuth and altitude angles of bright stars that meet the set conditions and are above the set level and can be observed; according to the current location and weather conditions, select at least one arbitrary star from the arbitrary star catalog;

[0010] 3) Drive the total station to point to the selected arbitrary star so that the selected arbitrary star is within the field of view of the total station telescope, and use the camera of the total station to obtain the star point pixel coordinates of the selected arbitrary star within the field of view of the total station telescope and the horizontal angle and altitude angle corresponding to the center of the crosshair of the total station telescope;

[0011] 4) Calculate the observed azimuth and altitude angles of the arbitrary star according to the star point pixel coordinates of the arbitrary star obtained in step 3), the horizontal angle and altitude angle corresponding to the center of the crosshair of the total station telescope, and the theoretical azimuth and altitude angles of the arbitrary star;

[0012] 5) Perform combined orientation according to the observed azimuth and altitude angles of each arbitrary star obtained.

[0013] The present invention first fixedly installs the geomagnetic north-seeking module on the total station, uses the geomagnetic module to achieve approximate orientation, and drives the total station to point to an arbitrary star based on the approximate orientation result to realize automatic tracking and observation of the arbitrary star, effectively improving the automation degree and observation efficiency of the orientation measurement; then performs precise astronomical orientation according to the pixel data of the arbitrary star captured by the total station and realizes high-precision calibration of the geomagnetic module, thereby realizing the complementary advantages of astronomical / geomagnetic orientation.

[0014] Further, the method also includes comparing the heading angles determined for each selected arbitrary star. If the difference between the heading angles is less than the set threshold, it indicates that the combined orientation is successful; otherwise, return to step 2) to reselect an arbitrary star from the arbitrary star catalog for orientation.

[0015] By comparing the differences between the heading angles obtained from each arbitrary star, when the difference is greater than the set threshold, it is considered that the combined orientation is unsuccessful, and an arbitrary star is reselected for reorientation. Through this inspection method, the present invention can further improve the orientation accuracy.

[0016] Further, the orientation process in step 5) includes:

[0017] A. Determine the astronomical longitude and astronomical latitude of the measuring station according to the observed altitude angle of the arbitrary star and the apparent right ascension and apparent declination of the arbitrary star;

[0018] B. Calculate the course angle based on the observed azimuth angle and the theoretical azimuth angle of any star, adjust the horizontal dial of the total station according to this course angle, and use this course angle as the geomagnetic orientation zero offset of the geomagnetic module.

[0019] The present invention can also determine the astronomical longitude and latitude of the measuring station according to the observed altitude angle of any star and the apparent right ascension and apparent declination of any star, realizing astronomical positioning; at the same time, after high-precision astronomical orientation is achieved by the total station, the course angle is used as the systematic error of geomagnetic orientation, and the geomagnetic orientation zero offset can be calibrated.

[0020] Further, the observed altitude angle used in calculating the astronomical longitude and latitude of the measuring station in step A is the true altitude angle after atmospheric refraction correction.

[0021] The present invention takes into account the influence of atmospheric refraction on the observed altitude angle of any star, corrects the observed altitude angle for atmospheric refraction when calculating the astronomical longitude and latitude of the measuring station using the observed altitude angle, and uses the corrected observed azimuth angle for astronomical positioning, further improving the positioning accuracy.

[0022] Further, in step B when calculating the course angle, the mean value of the course angles corresponding to each arbitrary star is used as the final course angle.

[0023] The present invention uses the mean value of the course angles determined by each arbitrary star as the final course angle for combined orientation to avoid errors caused by a single course angle.

[0024] Further, the set condition in step 2) is that the altitude angle range is 25° - 50°.

[0025] The present invention limits the altitude angle range to 25° - 50°, avoiding large astronomical orientation errors caused by both too high and too low altitude angles of the stars, and improving the orientation accuracy.

[0026] Further, the calculation formulas for the observed azimuth angle and altitude angle are as follows:

[0027]

[0028] Wherein, A s is the observed azimuth angle of any star, H s is the observed altitude angle of any star, a 11 , a 12 , a 21 and a 22 are calibration coefficients, (x 0 , y 0 ) is the pixel coordinate of the center of the crosshair of the total station telescope, (x, y) is the pixel coordinate of any star point, A c and Hc They are the horizontal angle and altitude angle corresponding to the center of the theodolite telescope crosshair respectively.

[0029] The present invention calculates the observation azimuth angle and altitude angle by using the calibration relationship between the camera and the theodolite telescope crosshair. The calculation model can be improved by the theodolite manufacturer, and the calculation is convenient and reliable.

[0030] Furthermore, the set threshold is determined by the angle measurement accuracy of the theodolite.

[0031] The present invention adaptively adjusts the set threshold according to the angle measurement accuracy, improving the reliability of the determination of whether the combined orientation is successful.

[0032] Furthermore, the calculation formula for the true altitude angle after atmospheric refraction correction in step A is:

[0033]

[0034] where H′ is the true altitude angle, H s is the observed altitude angle, with a range of -90 to 90°; p is the air pressure in hPa, and t is the temperature in K. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 is a flowchart of the astronomical / geomagnetic combined orientation method of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The following further describes the specific embodiments of the present invention with reference to the drawings.

[0037] The present invention initializes the orientation by setting a geomagnetic module inside the theodolite and using the geomagnetic module set inside the theodolite to obtain the heading angle and rough geomagnetic orientation of the theodolite; then drives the theodolite to point to any selected star according to the rough orientation result, so that the selected star is within the field of view of the theodolite telescope, and uses the camera of the theodolite to obtain the star point pixel coordinates of the selected star within the field of view of the theodolite telescope; then calculates the observed azimuth angle and altitude angle of the selected star according to the obtained star point pixel coordinates of the selected star, the horizontal angle and altitude angle corresponding to the center of the theodolite telescope crosshair, and the theoretical azimuth angle and altitude angle of the selected star; finally, performs combined orientation according to the obtained observed azimuth angles and altitude angles of each selected star. The implementation process of this method is as Figure 1 shown, and the following details its specific implementation process.

[0038] 1. Use the geomagnetic module for initial rough orientation.

[0039] The geomagnetic north-seeking module (such as the MCL601 geomagnetic north-seeking instrument produced by the 710 Research Institute of China State Shipbuilding Corporation) is horizontally and fixedly installed on the existing total station body. By using the rotating platform of the total station, the geomagnetic north-seeking module is driven to freely rotate in the horizontal direction. Plane multi-point position calibration is adopted to calibrate the geomagnetic module, and the heading angle information is output. The horizontal dial value of the total station is set to achieve geomagnetic approximate orientation.

[0040] 2. Generate an arbitrary star catalog and select an arbitrary star from it.

[0041] For observers in the Northern Hemisphere, there are more than 160 observable stars brighter than magnitude 3.0, which fully meets the need for arbitrary star orientation in terms of quantity. The smaller the magnitude value, the brighter the star. Stars brighter than magnitude 3.0 mean that the magnitude value is less than 3.0. Considering that stars with too high or too low altitude angles will both produce relatively large astronomical orientation errors, in this embodiment, the altitude angle range is limited to 25° to 50°, that is, only the bright stars with altitude angles within the above range are selected as arbitrary stars. According to the approximate longitude and latitude of the station, using the open-source NOVAS program package, all arbitrary bright stars that meet the conditions at the current moment are calculated and screened out, and their theoretical azimuth A, altitude angle H, apparent right ascension α, apparent declination δ, magnitude, etc. are output to generate an arbitrary star catalog. If the station is in an open area of the wild plain and the weather is clear, there are relatively many observable arbitrary stars. It is recommended to observe three stars to improve the combined orientation accuracy; if the station is in a canyon or urban area and it is a thin cloud weather, there are fewer observable arbitrary stars, then observing two stars is sufficient; if there is only one visible arbitrary star in the sky, combined orientation can also be carried out, but this star needs to be observed repeatedly to ensure the correctness of the orientation result. In this embodiment, three arbitrary stars are selected for observation.

[0042] 3. Use the total station to observe the selected arbitrary star and obtain the observed azimuth and altitude angle.

[0043] Find the theoretical azimuth A and theoretical altitude angle H of the selected arbitrary star from the arbitrary star catalog. According to the theoretical azimuth A and theoretical altitude angle H of the arbitrary star, drive the total station to automatically point to the azimuth of the selected arbitrary star. Since the geomagnetic orientation accuracy can reach 0.5 degrees and the field of view of the total station telescope is about 1.5 degrees, therefore, the arbitrary star will definitely be within the field of view of the total station telescope, that is, it can be observed by the total station telescope. When the total station points to the azimuth of the arbitrary star, start the total station camera to take pictures of the arbitrary star within the field of view of the total station telescope to obtain the star point pixel coordinates (x 1 , y 1), and record the imaging observation time; meanwhile, obtain the horizontal angle and altitude angle corresponding to the center of the total station telescope crosshair. According to the calibration relationship between the total station camera and the total station telescope crosshair, use the obtained star point pixel coordinates, the horizontal angle and altitude angle corresponding to the center of the total station telescope crosshair to calculate the observation azimuth angle and altitude angle of any star. The calculation model adopted by the present invention is provided by the total station manufacturer. Taking the first arbitrarily selected star as an example, the specific model is as follows:

[0044]

[0045] Where a 11 、a 12 、a 21 and a 22 are calibration coefficients, (x 0 , y 0 ) are the pixel coordinates of the center of the total station telescope crosshair, both of which can be obtained by calibration in the laboratory. To improve the reliability, repeat this step, observe the second and third arbitrarily selected stars, and obtain their observation azimuth angles and altitude angles (A s2 , H s2 ), (A s3 , H s3 ).

[0046] 4. Orient using the obtained observation azimuth angles and altitude angles of the selected arbitrarily selected stars.

[0047] According to the classical altitude method astronomical positioning model, use the obtained observation altitude angles of each arbitrarily selected star to solve by the least squares method to accurately determine the astronomical longitude and astronomical latitude of the station; due to the influence of atmospheric refraction, there is a certain difference between the calculated observation altitude angle and the true observation altitude angle. To avoid the insufficient accuracy of the calculated astronomical longitude and astronomical latitude caused by this difference, the present invention first calculates the atmospheric refraction correction value ρ to obtain the true observation altitude angle, and uses the true observation altitude angle to calculate the astronomical longitude and astronomical latitude of the station. Among them, the calculation model of the atmospheric refraction correction value ρ is as follows:

[0048]

[0049] Where p in the formula is the air pressure, the unit is hPa, t is the temperature, the unit is K, and the unit of the calculated atmospheric refraction correction value is arcseconds.

[0050] Using the obtained atmospheric refraction correction value, the astronomical longitude λ and astronomical latitude of the station can be accurately calculated Taking three arbitrarily selected stars as an example, the calculation formula adopted is:

[0051]

[0052] S is the Greenwich true sidereal time of the observation epoch of the i-th arbitrary star, which is obtained by converting the measured instantaneous UTC time; α i , δ i are the apparent right ascension and apparent declination of the i-th arbitrary star, which are obtained from the arbitrary star catalog. H s1 is the observed altitude angle of the i-th arbitrary star.

[0053] Since the arbitrary stars are basically not near the Earth's axis of rotation (except the North Star), their azimuth angles change relatively fast. Therefore, according to the imaging observation time information and the precise astronomical longitude and latitude of the station, the NOVAS package is used again to accurately calculate the theoretical azimuth angles A 1 ′, A 2 ′ and A 3 ′ of the three arbitrary stars. And the heading angles (i.e., geomagnetic orientation errors) θ 1 , θ 2 and θ 3 are accurately calculated:

[0054]

[0055] It is judged whether the combined orientation is successful according to the calculated heading angles corresponding to each arbitrary star. If the mutual difference between the three heading angles is less than a certain threshold, it is considered that the combined orientation is successful. The specific setting of the threshold needs to be determined according to the angular measurement accuracy of the total station. For example, if a total station has a nominal angular measurement accuracy of 2″ (1σ), taking 3σ as the standard, the threshold can be set to about 12″. If the above conditions are not met, it is considered that the combined orientation is not successful, and then it is necessary to reselect arbitrary stars from the arbitrary star catalog and repeat steps 3 and 4 until the mutual difference between the heading angles obtained from the selected arbitrary stars is less than the set threshold.

[0056] When the combined orientation meets the success conditions, after observing the arbitrary stars, the total station is not rotated. Take the average value of the heading angles as the final result, and modify the horizontal circle to At this time, the 0° direction of the total station horizontal circle points to true north, and the total station completes the precise astronomical orientation. At the same time, is also the orientation system error of the geomagnetic module at the local station, that is, the geomagnetic orientation zero offset. θ can be used as a constant in the geomagnetic orientation application to improve the accuracy of the geomagnetic orientation.

[0057] From the above combined orientation process, it can be seen that the advantages of the present invention are mainly reflected in: 1) Without manual intervention, it can achieve automatic tracking and observation of any star, effectively improving the automation degree and observation efficiency of orientation measurement; 2) There is no need to track and observe any star for several minutes. The identification of any star has been achieved while observing, avoiding the subsequent complex identification algorithm of any star based on angular distance matching; 3) The geomagnetic module assists the total station to achieve automatic tracking and observation of any star. After the total station achieves high-precision astronomical orientation, it can calibrate the zero bias of geomagnetic orientation. The two achieve true complementary advantages; 4) The present invention not only achieves high-precision combined orientation, but also achieves astronomical positioning, and the output astronomical longitude and latitude also have certain application value; 5) For any region in the world, there are hundreds of observable stars (magnitude brighter than 3.0). The operator can make a flexible choice according to visible conditions such as terrain and weather. Therefore, the orientation measurement is not restricted by geographical conditions and has stronger usability.

[0058] In order to further illustrate the effect of the present invention, the combined orientation method of the present invention was tested in a field environment. The RTS010A image total station produced by Suzhou First Optical Instrument Factory was used in this experiment, and the angular measurement accuracy was 2"; the geomagnetic module used the MCL601 geomagnetic north finder produced by the 710th Research Institute of China State Shipbuilding Corporation, and the orientation accuracy was about 0.3° (3σ); the computer used ThinkPad E450, and the operating environment of the control and data processing program was VS2013. On the night of April 23, 2022, under clear night conditions in North China, 5 combined orientation experiments were carried out on the known astronomical azimuth side, and all 5 experiments were successful. The experimental results are shown in Table 1.

[0059] Table 1

[0060]

[0061]

[0062] As shown in Table 1, the difference between the heading angles calculated in the 5 experiments and the average value is within 10", which is relatively stable. There is an obvious systematic error in the calculated heading angle, about 129.4", and this value can be used as the zero bias value of geomagnetic orientation and written into the geomagnetic orientation module. The time used for the five orientation experiments is about 1 minute. Compared with the current human eye or image observation of any star (the observation of a single star requires 1-2 minutes), the observation time is shortened by at least 2 / 3. Generally speaking, the present invention is completely practical and feasible, and both the orientation accuracy and the measurement efficiency are relatively high.

Claims

1. An astronomical / geomagnetic combined orientation method, characterized in that, the method comprises the following steps: 1) Use the geomagnetic module set in the total station for initial orientation to obtain the initial heading angle of the total station and the geomagnetic approximate orientation; 2) Obtain an arbitrary star catalog, which includes the theoretical azimuth and altitude angles of bright stars above a set level that meet the set conditions and are observable; according to the current location and weather conditions, select at least one arbitrary star from the arbitrary star catalog; 3) Drive the total station to point to the selected arbitrary star so that the selected arbitrary star is within the field of view of the total station telescope, and use the camera of the total station to obtain the star point pixel coordinates of the selected arbitrary star within the field of view of the total station telescope and the horizontal angle and altitude angle corresponding to the center of the crosshair of the total station telescope; 4) Calculate the observed azimuth and altitude angles of the arbitrary star according to the star point pixel coordinates of the arbitrary star obtained in step 3), the horizontal angle and altitude angle corresponding to the center of the crosshair of the total station telescope, and the theoretical azimuth and altitude angles of the arbitrary star; 5) Perform combined orientation according to the observed azimuth and altitude angles of each arbitrary star obtained.

2. The astronomical / geomagnetic combined orientation method according to claim 1, characterized in that, the method further includes comparing the heading angles determined for each selected arbitrary star. If the difference between the heading angles is less than the set threshold, it indicates that the combined orientation is successful; otherwise, return to step 2) to re-select an arbitrary star from the arbitrary star catalog for orientation.

3. The astronomical / geomagnetic combined orientation method according to claim 1 or 2, characterized in that, the orientation process in step 5) includes: A. Determine the astronomical longitude and latitude of the station according to the observed altitude angle of the arbitrary star and the apparent right ascension and declination of the arbitrary star; B. Calculate the heading angle according to the observed azimuth and theoretical azimuth of the arbitrary star, adjust the horizontal dial of the total station according to the heading angle, and use the heading angle as the geomagnetic orientation zero offset of the geomagnetic module.

4. The astronomical / geomagnetic combined orientation method according to claim 3, characterized in that, the observed altitude angle used in calculating the astronomical longitude and latitude of the station in step A is the true altitude angle after atmospheric refraction correction.

5. The astronomical / geomagnetic combined orientation method according to claim 3, characterized in that, when calculating the heading angle in step B, the mean value of the heading angles corresponding to each arbitrary star is used as the final heading angle.

6. The astronomical / geomagnetic combined orientation method according to claim 1 or 2, characterized in that, the set condition in step 2) is that the altitude angle range is 25° to 50°.

7. The astronomical / geomagnetic combined orientation method according to claim 3, characterized in that, the calculation formulas for the observed azimuth and altitude angles are: Among them, A s is the observed azimuth angle of any star, H s is the observed altitude angle of any star, a 11 , a 12 , a 21 and a 22 are calibration coefficients, (x 0 , y 0 ) is the pixel coordinate of the center of the theodolite telescope crosshair, (x, y) is the pixel coordinate of any star point, A c and H c are the horizontal angle and altitude angle corresponding to the center of the theodolite telescope crosshair respectively.

8. The astronomical / geomagnetic combined orientation method according to claim 2, characterized in that, the set threshold is determined by the angular measurement accuracy of the total station.

9. The astronomical / geomagnetic combined orientation method according to claim 4, characterized in that, the calculation formula for the true altitude angle after atmospheric refraction correction in step A is: where H s ′ is the true altitude angle, and H s is the observed altitude angle, with a range of -90 to 90°; p is the air pressure in hPa, and t is the temperature in K.

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