Inter-vehicle distance estimation device

Abstract

To provide an inter-vehicle distance estimation device for improving estimation accuracy of inter-vehicle distance between an own vehicle and a preceding vehicle based on a captured image of a front camera.SOLUTION: An inter-vehicle distance estimation device for estimating inter-vehicle distance between an own vehicle and a preceding vehicle from a vehicle width and a vehicle assumed width of the preceding vehicle based on a captured image of a front camera of the own vehicle includes: a first ratio calculation unit for calculating a first ratio that is a ratio between the vehicle width of the preceding vehicle on the captured image and a first lane width corresponding to the preceding vehicle on the captured image; a second ratio calculation unit for calculating a second ratio that is a ratio between a second lane width corresponding to a position in front of the own vehicle by certain distance on the captured image and an on-image vehicle assumed width that is the vehicle assumed width projected to the position in front of the own vehicle by certain distance on the captured image; a width correction unit for correcting the vehicle assumed width according to the first lane width and the first ratio when it is determined that an absolute value of difference between the first ratio and the second ratio is equal to or greater than a ratio threshold; and an inter-vehicle distance estimation unit for estimating inter-vehicle distance using the vehicle assumed width after correction.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to an inter-vehicle distance estimation device. [Background technology]

[0002] Japanese Patent Application Laid-Open Publication No. 2012-159469 is a known technical document relating to a vehicle distance estimation device. This publication describes a device that measures the distance to a target such as a preceding vehicle by using the size of a road sign on an image captured by a camera of the vehicle. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2012-159469 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, road signs are not always present in the captured image, so a more general-purpose method for estimating the distance between the host vehicle and the preceding vehicle is needed. [Means for solving the problem]

[0005] One aspect of the present invention is an inter-vehicle distance estimation device that estimates an inter-vehicle distance between a host vehicle and a preceding vehicle based on an image captured by a front camera of the host vehicle from the vehicle width of the preceding vehicle in the captured image and a preset vehicle assumed width, the device including a first ratio calculation unit that calculates a first ratio, which is a ratio between the vehicle width of the preceding vehicle in the captured image and a first lane width that is a lane width corresponding to the preceding vehicle in the captured image, based on the image captured by the front camera, and a second lane width that is a lane width corresponding to a position a certain distance forward from the host vehicle in the captured image and a first lane width that is a lane width corresponding to a position a certain distance forward from the host vehicle in the captured image, based on the image captured by the front camera. The system includes a second ratio calculation unit that calculates a second ratio, which is a ratio between the first ratio and the image-based assumed vehicle width, which is the assumed vehicle width projected at a position a fixed distance forward; a ratio determination unit that determines whether or not an absolute value of a difference between the first ratio and the second ratio is equal to or greater than a ratio threshold; a width correction unit that corrects the assumed vehicle width in accordance with the first lane width and the first ratio when the ratio determination unit determines that the absolute value of the difference between the first ratio and the second ratio is equal to or greater than the ratio threshold; and an inter-vehicle distance estimation unit that estimates a distance between the host vehicle and a preceding vehicle using the corrected assumed vehicle width when the assumed vehicle width has been corrected by the width correction unit. Effect of the Invention

[0006] According to one aspect of the present invention, it is possible to improve the accuracy of estimating the inter-vehicle distance between the host vehicle and a preceding vehicle based on an image captured by a forward camera. [Brief description of the drawings]

[0007] [Figure 1] 1 is a block diagram showing an inter-vehicle distance estimation device according to an embodiment; [Diagram 2] FIG. 4 is a plan view for explaining a method for estimating a vehicle distance; [Diagram 3] FIG. 11 is a plan view for explaining calculation of a first ratio. [Figure 4] 11A and 11B are diagrams for explaining a vehicle width and a first lane width on a captured image. [Diagram 5] FIG. 11 is a plan view for explaining a second lane width. [Figure 6]1A is a diagram for explaining how to obtain the lateral position of the assumed vehicle width on the image, and FIG. 1B is a diagram for explaining how to obtain the longitudinal position of the assumed vehicle width on the image. [Figure 7] FIG. 13 is a diagram for explaining an assumed vehicle width on an image. [Figure 8] 10 is a flowchart showing an example of a vehicle distance estimation process. [Figure 9] 13A is a plan view illustrating a method for recognizing a lane width in a modified example, and FIG. 13B is a view illustrating fitting of a white line on a captured image with a white line on map information. [Figure 10] FIG. 13(a) is a plan view for explaining a method for calculating a second ratio in the modified example; FIG. 13(b) is a view for explaining a method for calculating a second ratio in the modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0009] The inter-vehicle distance estimation device 100 shown in Fig. 1 is mounted on a vehicle such as a passenger car (hereinafter referred to as the host vehicle) and estimates the inter-vehicle distance between the host vehicle and a preceding vehicle. The inter-vehicle distance estimation device 100 estimates the inter-vehicle distance between the host vehicle and the preceding vehicle using an image captured by a front camera 1 mounted on the host vehicle. The preceding vehicle is a vehicle traveling just ahead of the host vehicle on the lane in which the host vehicle is traveling.

[0010] The front camera 1 is an imaging device that captures an image of the situation in front of the vehicle. The front camera 1 is provided, for example, behind the windshield of the vehicle. The front camera 1 is, for example, a monocular camera.

[0011] Fig. 2 is a diagram for explaining an example of a method for estimating the distance between vehicles. Fig. 2 shows a preceding vehicle N, an image plane G, an assumed vehicle width W, a vehicle width x on a captured image, an inter-vehicle distance Z, and a plane angle θ based on the lens center of the front camera 1. The assumed vehicle width W and the inter-vehicle distance Z are in meters, and the vehicle width x on the image is in pixels.

[0012] The assumed vehicle width W is a width assumed as the vehicle width of the preceding vehicle for estimating the inter-vehicle distance Z. The assumed vehicle width W is a width with a preset value, and is corrected by a width correction unit 14 described later. As shown in FIG. 2, the inter-vehicle distance estimation device 100 estimates the inter-vehicle distance Z between the host vehicle and the preceding vehicle using the vehicle width x of the preceding vehicle on the captured image and the assumed vehicle width W. The estimation of the inter-vehicle distance Z will be described in detail later.

[0013] [Configuration of vehicle distance estimation device] The configuration of the inter-vehicle distance estimation device 100 according to this embodiment will be described below. As shown in FIG. 1, the inter-vehicle distance estimation device 100 includes an ECU [Electronic Control Unit] 10 that manages the device. The ECU 10 is an electronic control unit having a CPU [Central Processing Unit] and a storage unit such as a ROM [Read Only Memory] or a RAM [Random Access Memory]. The ECU 10 realizes various functions by, for example, executing a program stored in the storage unit by the CPU. The ECU 10 may be composed of a plurality of electronic units. The ECU 10 is connected to a front camera 1.

[0014] The following describes the functional configuration of the ECU 10. As shown in FIG 1, the ECU 10 has a first ratio calculation unit 11, a second ratio calculation unit 12, a ratio determination unit 13, a width correction unit 14, and an inter-vehicle distance estimation unit 15.

[0015] Based on the captured image of the front camera 1, the first ratio calculation unit 11 calculates a first ratio, which is a ratio between the vehicle width x of the preceding vehicle N on the captured image and a first lane width that is a lane width corresponding to the preceding vehicle N on the captured image. Fig. 3 is a plan view for explaining the calculation of the first ratio. Fig. 3 shows a lane R, a lane width LA corresponding to the preceding vehicle N, a vehicle width X of the preceding vehicle N, a first lane width La on the captured image, and a vehicle width x on the captured image. The lane width LA corresponding to the preceding vehicle N and the vehicle width X of the preceding vehicle N are expressed in meters, and the first lane width La on the image is expressed in pixels.

[0016] Fig. 4 is a diagram for explaining the vehicle width and lane width on the captured image. Fig. 4 shows the preceding vehicle recognition result Nc, the white line recognition result B, and the lower end position U of the preceding vehicle. As shown in Fig. 4, the first ratio calculation unit 11 recognizes the vehicle width x of the preceding vehicle on the captured image from the preceding vehicle recognition result Nc in the captured image.

[0017] The first ratio calculation unit 11 also recognizes the first lane width La on the image corresponding to the preceding vehicle N from the length of a straight line connecting the intersection between the preceding vehicle lower end position U, which is the position of the lower end of the frame of the preceding vehicle recognition result Nc on the captured image, and the white line recognition result B, which is the recognition result of two white lines. Note that the method of recognizing the first lane width La is not particularly limited, and any well-known method can be adopted. The first ratio calculation unit 11 calculates the first ratio from the vehicle width x of the preceding vehicle on the captured image and the first lane width La on the captured image.

[0018] The second ratio calculation unit 12 calculates, based on the image captured by the forward camera 1, a second ratio which is the ratio between the second lane width, which is the lane width at a position a certain distance D forward from the host vehicle on the captured image, and the image vehicle expected width W, which is the vehicle expected width projected at a position a certain distance D forward from the host vehicle on the captured image.

[0019] Fig. 5 is a plan view for explaining the second lane width. Fig. 5 shows a certain distance D, a lane width LB at a position the certain distance D ahead of the vehicle, a second lane width Lb on the captured image, an assumed vehicle width W at a position the certain distance D ahead of the vehicle, and an assumed vehicle width w on the image.

[0020] The certain distance D is a distance of a preset value. The certain distance D may be a fixed value, or may be a distance that is shorter than the preceding vehicle N. The certain distance D may be corrected to be a distance shorter than the preceding vehicle distance Z estimated one time previously. The second lane width Lb is a lane width obtained by projecting the lane width LB at a position a certain distance D ahead of the host vehicle onto the captured image. The lane width LB is measured in meters, and the second lane width Lb is measured in pixels. As shown in FIG. 5, the second ratio calculation unit 12 recognizes the second lane width Lb obtained by projecting the lane width LB at a position a certain distance D ahead of the host vehicle onto the captured image.

[0021] Fig. 6(a) is a diagram for explaining how to obtain the lateral position of the assumed vehicle width w on an image. Fig. 6(a) shows the angle θw between the host vehicle M, a fixed distance D, and the assumed vehicle width W. Fig. 6(b) is a diagram for explaining how to obtain the longitudinal position of the assumed vehicle width w on an image. Fig. 6(b) shows the camera mounting height H, and the angle θh between the fixed distance D and the camera mounting height H. The camera mounting height H is the height at which the front camera 1 is mounted.

[0022] FIG. 7 is a diagram for explaining the assumed vehicle width w on the image. FOE is the focus of expansion of the front camera 1. As shown in FIG. 6(a), FIG. 6(b) and FIG. 7, the second ratio calculation unit 12 can, for example, obtain the lateral position of the assumed vehicle width w on the image from the angle θw between the fixed distance D and the assumed vehicle width W, and obtain the height h (vertical position) of the assumed vehicle width w on the image from the angle θh between the fixed distance D and the camera mounting height H. As a result, the second ratio calculation unit 12 recognizes the assumed vehicle width w on the image obtained by projecting the assumed vehicle width W at a position forward of the vehicle M by a fixed distance D onto the captured image. The second ratio calculation unit 12 calculates the second ratio from the second lane width Lb and the assumed vehicle width w on the image.

[0023] The ratio determination unit 13 determines whether or not the absolute value of the difference between the first ratio and the second ratio is equal to or greater than a ratio threshold value, based on the first ratio calculated by the first ratio calculation unit 11 and the second ratio calculated by the second ratio calculation unit 12. The ratio threshold value is a threshold value of a preset value.

[0024] When the ratio determination unit 13 determines that the absolute value of the difference between the first ratio and the second ratio is equal to or greater than the ratio threshold, the width correction unit 14 corrects the vehicle assumed width W according to the first lane width La and the first ratio. The width correction unit 14 corrects the length of the vehicle assumed width W so that the ratio between the corrected vehicle assumed width W and the first lane width La approaches the first ratio. The width correction unit 14 may correct the length of the vehicle assumed width W so that the second ratio using the corrected vehicle assumed width W approaches the first ratio. The width correction unit 14 may correct the vehicle assumed width W so that the ratio between the corrected vehicle assumed width W and the first lane width La is the same value as the first ratio, or may correct the length of the vehicle assumed width W so that the second ratio using the corrected vehicle assumed width W is the same value as the first ratio.

[0025] The inter-vehicle distance estimation unit 15 estimates the inter-vehicle distance Z between the host vehicle M and the preceding vehicle N. The inter-vehicle distance estimation unit 15 estimates the inter-vehicle distance Z based on the assumed vehicle width W, the vehicle width x in the captured image, the camera resolution α, and the plane angle θ based on the lens center of the front camera 1 (see FIG. 2). The camera resolution α is the camera resolution of the front camera 1. The camera resolution α is, for example, a fixed value.

[0026] The inter-vehicle distance estimating unit 15 estimates the inter-vehicle distance Z from the assumed vehicle width W, the vehicle width x in the captured image, the camera resolution α, and the plane angle θ, for example, using the following equations (1) to (3).

number

[0027] When the assumed vehicle width W is corrected by the width correcting unit 14, the inter-vehicle distance estimating unit 15 estimates the inter-vehicle distance Z using the assumed vehicle width W after correction.

[0028] [Processing by vehicle distance estimation device] Next, the processing of the inter-vehicle distance estimation device 100 according to this embodiment will be described with reference to Fig. 8. Fig. 8 is a flowchart showing an example of the inter-vehicle distance estimation processing.

[0029] 8, the ECU 10 of the inter-vehicle distance estimation device 100 calculates a first ratio by the first ratio calculation unit 11 in S10. The first ratio calculation unit 11 calculates a first ratio, which is a ratio between the vehicle width x of the preceding vehicle on the captured image and the first lane width, which is the lane width corresponding to the preceding vehicle N on the captured image, based on the captured image of the front camera 1. After that, the ECU 10 proceeds to S11.

[0030] In S11, the ECU 10 calculates a second ratio by the second ratio calculation unit 12. The second ratio calculation unit 12 calculates a second ratio, which is a ratio between a second lane width, which is a lane width at a position a certain distance D forward from the host vehicle M on the captured image, and an assumed vehicle width on the image, which is an assumed vehicle width W projected at a position a certain distance D forward from the host vehicle M on the captured image, based on the captured image of the front camera 1. Thereafter, the ECU 10 proceeds to S12.

[0031] In S12, the ECU 10 determines whether or not the absolute value of the difference between the first ratio and the second ratio is equal to or greater than the ratio threshold value using the ratio determination unit 13. If the ECU 10 determines that the absolute value of the difference between the first ratio and the second ratio is equal to or greater than the ratio threshold value (S12: YES), the ECU 10 proceeds to S13. If the ECU 10 does not determine that the absolute value of the difference between the first ratio and the second ratio is equal to or greater than the ratio threshold value (S12: NO), the ECU 10 proceeds to S14.

[0032] In S13, the ECU 10 corrects the assumed vehicle width W according to the first lane width La and the first ratio by the width corrector 14. The width corrector 14 corrects the length of the assumed vehicle width W so that the ratio between the corrected assumed vehicle width W and the first lane width La approaches the first ratio. After that, the ECU 10 proceeds to S14.

[0033] In S14, the ECU 10 estimates the inter-vehicle distance Z between the host vehicle M and the preceding vehicle by the inter-vehicle distance estimation unit 15. The inter-vehicle distance estimation unit 15 estimates the inter-vehicle distance Z by using, for example, the above-mentioned formulas (1) to (3) based on the assumed vehicle width W, the vehicle width x in the captured image, the camera resolution α, and the plane angle θ based on the lens center of the front camera 1. Thereafter, the ECU 10 ends the current inter-vehicle distance estimation process.

[0034] According to the inter-vehicle distance estimation device 100 of this embodiment described above, the vehicle width of the preceding vehicle N and the lane width of the lane in which the host vehicle M is traveling are recognized from the image captured by the forward camera 1, and if the absolute value of the difference between the first ratio and the second ratio is equal to or greater than the ratio threshold, the expected vehicle width W is corrected according to the first lane width La and the first ratio. Therefore, when the expected vehicle width W significantly deviates from the actual vehicle width of the preceding vehicle N, it is possible to avoid using it as is to estimate the inter-vehicle distance Z, and the estimation accuracy of the inter-vehicle distance Z can be improved.

[0035] Although the embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment. The present invention can be embodied in various forms including the above-mentioned embodiment and various modifications and improvements based on the knowledge of those skilled in the art.

[0036] [Variations] Modified examples of the inter-vehicle distance estimation device 100 will be described below with reference to the drawings. Fig. 9(a) is a plan view for explaining a method of recognizing a lane width in the modified example. Fig. 9(a) shows a white line BA, a lane width LC corresponding to the preceding vehicle N, and a first lane width Lc on an image. The first lane width Lc is the lane width LC corresponding to the preceding vehicle N on a captured image. Fig. 9(a) assumes a case where the lane width of the road has changed and the lane width in the vicinity of the host vehicle M and the lane width LC corresponding to the preceding vehicle N are different.

[0037] In the inter-vehicle distance estimation device 100 according to the modified example, the lane width is acquired from map information in the calculation of the first ratio by the first ratio calculation unit 11. The inter-vehicle distance estimation device 100 recognizes the position of the host vehicle M from, for example, a global navigation satellite system (GSSN) or the like, and acquires the lane width of the lane in which the host vehicle M is traveling from a map database of the host vehicle M or a map information server outside the vehicle.

[0038] Fig. 9(b) is a diagram for explaining fitting between a white line on a captured image and a white line on map information. Fig. 9(b) shows a white line Ba on a captured image and a white line Bm on map information. The first ratio calculation unit 11 recognizes a lane width corresponding to a position on the captured image from the lane width on the map information by fitting the white line Ba on the captured image to the white line Bm on the map information as shown in Fig. 9(b).

[0039] In addition, since the camera resolution becomes coarser and the fitting error becomes larger the further away from the vehicle M, the area of ​​the captured image can be divided into multiple areas (for example, at intervals of several meters) according to the distance from the vehicle M, and the average lane width in each area can be used as the lane width for that area.

[0040] In the vehicle distance estimation device 100 according to the modified example, when there is a difference between the lane width corresponding to the preceding vehicle N and the lane width at a certain distance D from the host vehicle M, the second ratio calculation unit 12 may calculate the second ratio taking into account that difference.

[0041] FIG. 10(a) is a plan view for explaining a method of calculating the second ratio in the modified example. In FIG. 10(a), the lane width of the road changes as in FIG. 9(a). FIG. 10(a) shows the lane width LC corresponding to the preceding vehicle N and the lane width LD of a certain distance D. FIG. 10(b) is a diagram for explaining a method of calculating the second ratio in the modified example. In FIG. 10, a position corresponding to the certain distance D, a first lane width Lc on the image, and a second lane width Ld on the image are shown. The second lane width Ld is the lane width LD of the certain distance D on the captured image.

[0042] 10(a) and 10(b), the second ratio calculation unit 12 may project the assumed vehicle width W onto a position at a certain distance D from the host vehicle M on the captured image (b), and may also project a first lane width Lc corresponding to the preceding vehicle N, and calculate the second ratio using the assumed vehicle width w on the captured image and the first lane width Lc. That is, the second ratio may be calculated by regarding the first lane width Lc as the second lane width Ld. [Explanation of symbols]

[0043] 1...forward camera, 10...ECU, 11...first ratio calculation unit, 12...second ratio calculation unit, 13...ratio determination unit, 14...width correction unit, 15...inter-vehicle distance estimation unit, 100...inter-vehicle distance estimation device.

Claims

[Claim 1] 1. A vehicle distance estimation device that estimates a vehicle distance between a vehicle and a preceding vehicle based on a vehicle width of the preceding vehicle on an image captured by a front camera of the vehicle, the vehicle distance estimation device comprising: a first ratio calculation unit that calculates, based on an image captured by the front camera, a first ratio that is a ratio between a vehicle width of the preceding vehicle on the captured image and a first lane width that is a lane width corresponding to the preceding vehicle on the captured image; a second ratio calculation unit that calculates, based on an image captured by the front camera, a second ratio that is a ratio between a second lane width that is a lane width corresponding to a position a certain distance forward from the host vehicle on the captured image and an image assumed vehicle width that is the assumed vehicle width projected at a position the certain distance forward from the host vehicle on the captured image; a ratio determination unit that determines whether or not an absolute value of a difference between the first ratio and the second ratio is equal to or greater than a ratio threshold; a width correction unit that corrects the vehicle assumed width in accordance with the first lane width and the first ratio when the ratio determination unit determines that an absolute value of the difference between the first ratio and the second ratio is equal to or greater than a ratio threshold value; a vehicle distance estimation unit that estimates a vehicle distance between the host vehicle and the preceding vehicle using the corrected assumed vehicle width when the assumed vehicle width is corrected by the width correction unit; A vehicle distance estimation device comprising:

Images