KR20190083774A - Apparatus and method for calculating distance between vehicles using 3-channel camera - Google Patents

Abstract

According to one embodiment of the present invention, a method for calculating a distance between vehicles using a three-channel camera can comprise: a step of acquiring a side and a front image by using a half mirror for a camera installed in a first side and a second side of the vehicle; a step of recognizing a front vehicle on the basis of the front camera; a step of distinguishing a recognizing region of the recognized front vehicle, and selecting a camera corresponding to the distinguished recognizing region; and a step of measuring a distance between the vehicles on the basis of the selected camera image.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a three-channel camera,

The present invention relates to an apparatus and method for calculating an inter-vehicle distance using a three-channel camera.

The conventional inter-vehicle distance calculating method calculates the inter-vehicle distance based on the camera of the front camera or the camera peripheral image providing device installed on the first side and the second side of the vehicle.

Fig. 1 is a block diagram showing a configuration of a car-to-car calculation method according to the prior art.

Referring to FIG. 1, in the conventional vehicle-to-vehicle distance calculating method, a license plate width of a front vehicle or width and lane of a vehicle in a front camera as a single camera are recognized and compared with lane data and pre- (S110, S111, S112). Alternatively, the left and right cameras are installed in the vehicle, and the corrected left and right images are detected from the captured image signals to recognize the vehicle and estimate the inter-vehicle distance (S120, S121, S122). Then, the estimated inter-vehicle distance is provided to the driver's apparatus (S130).

In the case of using a single camera, there is an accuracy member and a blind spot according to the change of the road state due to the unidirectional information use. In the case of using the conventional stereoscopic vision, There is a problem that the measured value of the blind vehicle is not reliable due to the presence of a blind spot on the right side of the vehicle.

The present invention proposes an apparatus and method for calculating an inter-vehicle distance using a three-channel camera.

More specifically, a half mirror (Half Mirror) is combined with the camera of the peripheral image providing apparatus, so that the functions of the existing peripheral image providing apparatus and the forward image can be utilized. Also, Provided is an apparatus and method for calculating an inter-vehicle distance using a 3-channel camera that improves the accuracy and cover area by improving the measurement of the inter-vehicle distance by using the camera.

The problems of the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a method for calculating an inter-vehicle distance using a three-channel camera, the method comprising: acquiring side and front images using a half mirror of a camera installed on a first side and a second side of the vehicle; Recognizing a forward vehicle based on a forward camera; Identifying a recognized area of the recognized forward vehicle, and selecting a camera corresponding to the recognized area; And measuring an inter-vehicle distance based on the selected camera image.

According to the embodiment, the step of the camera installed on the first side and the second side of the vehicle utilizing the half mirror to acquire the side and front images may be a step of determining whether the state of the vehicle is the running state, ; Supplying current to the half mirror based on the supply current control in the case of the inter-vehicle distance measurement mode; Activating a supply current of a half mirror disposed in the camera; And receiving the front and side images of the camera corresponding to the half mirror.

According to an embodiment of the present invention, the side image of the input camera image is utilized as top view and dead zone detection system information of a peripheral image providing apparatus. And using the front image among the camera images installed on the first side and the second side of the vehicle as a three-channel camera; .

According to an embodiment, the step of inputting the front and side images by the camera corresponding to the half mirror includes supplying current to the half mirror when the supply current of the half mirror is activated; Repeatedly adjusting currents for the camera to input the front and side images for each frame; Receiving the front and side images by adjusting reflectance and transmittance of the half mirror based on the adjusted current; And using the input front and side images as a corresponding image stereo vision.

According to the embodiment, the step of recognizing the front vehicle based on the front camera can recognize the front vehicle based on the front camera having the measurement area of 0 to 190 degrees.

According to an embodiment of the present invention, the step of discriminating the recognition area of the recognized front vehicle and the step of selecting the camera corresponding to the divided recognition area may include the step of, when the front vehicle is located in the area where the measurement area is 0 degrees or 45 degrees, And measuring an inter-vehicle distance based on the first camera and the forward camera.

According to an embodiment of the present invention, the step of discriminating the recognition area of the recognized front vehicle and the step of selecting the camera corresponding to the divided recognition area may include the step of, when the front vehicle is located in the area where the measurement area is 45 degrees to 145 degrees, And measuring an inter-vehicle distance based on the first camera and the second camera.

According to an embodiment of the present invention, the step of distinguishing the recognition area of the recognized front vehicle and the step of selecting a camera corresponding to the recognized recognition area may include: if the front vehicle is located in an area where the measurement area is 145 degrees to 190 degrees, And measuring an inter-vehicle distance based on the front camera and the second camera.

According to an embodiment, the step of measuring the headway distance based on the selected camera image includes: obtaining coordinate information based on the camera image correction; Performing triangulation based on the coordinates of the pre-stored camera and the feature points of the preceding vehicle; And obtaining an inter-vehicle distance according to the triangulation method.

According to an aspect of the present invention, there is provided an apparatus for calculating an inter-vehicle distance using a three-channel camera, including: a camera installed on a first side and a second side of a vehicle for acquiring side and front images using a half mirror; A front camera for recognizing a front vehicle; And a processor that identifies the recognition area of the recognized forward vehicle, selects a camera corresponding to the recognized recognition area, and measures the inter-vehicle distance based on the selected camera image.

According to the embodiment, the processor determines whether the vehicle is in a running state or a forward vehicle-to-vehicle distance measuring mode, and in the case of the inter-vehicle distance measuring mode, supplies a current to the half mirror based on the supply current control , The supply current of the half mirror disposed in the camera is activated, and the front and side images are received from the camera corresponding to the half mirror.

According to an embodiment of the present invention, the processor uses the side image of the input camera image as the top view and the dead zone detection system information of the peripheral image providing apparatus, and uses the front side of the camera images installed on the first side and the second side of the vehicle The image can be used as a 3-channel camera.

According to an embodiment, the processor supplies a current to the half mirror when activating a supply current of the half mirror, and the camera repeatedly adjusts current to input a frame-by-frame front and side image, The front and side images can be received by adjusting the reflectance and transmittance of the half mirror based on the received image data and the received front and side images can be used as a corresponding image stereo vision.

According to an embodiment, the processor is able to recognize the front vehicle based on the front camera whose measurement area is between 0 and 190 degrees.

According to an embodiment, the processor can measure the headway distance based on the first camera and the front camera when the front vehicle is located in an area where the measurement area is 0 degrees or 45 degrees.

According to an embodiment, the processor can measure the headway distance based on the first camera and the second camera when the front vehicle is located in an area where the measurement area is 45 degrees to 145 degrees.

According to the embodiment, the processor may measure the headway distance based on the front camera and the second camera when the front vehicle is located in an area where the measurement area is 145 degrees to 190 degrees.

According to the embodiment, the processor obtains the coordinate information based on the camera image correction, performs triangulation based on the coordinates of the previously stored camera, the feature points of the preceding vehicle, and obtains the inter-vehicle distance according to the triangulation method .

The effects of the apparatus and method for calculating the headway distance using the 3-channel camera according to the present invention will be described as follows.

First, by adding only the half mirror part which can control the reflectance / transmittance through the current control to the existing camera, it is possible to recognize the inter-vehicle distance to the whole area in the forward direction without using the rider as well as the function of the existing peripheral image providing device without blind spot There are advantages that can be applied to ADAS field.

Second, the accuracy and cover area are improved compared with the system using single camera and simple stereo vision.

Thirdly, it is easy to image the area by securing the 3-channel image and it is advantageous that the accuracy of the inter-vehicle distance can be secured even in various environments

The effects obtained by the present invention are not limited to the above-mentioned effects, and other effects not mentioned can be clearly understood by those skilled in the art from the following description will be.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. It is to be understood, however, that the technical features of the present invention are not limited to the specific drawings, and the features disclosed in the drawings may be combined with each other to constitute a new embodiment.
Fig. 1 is a block diagram showing a configuration of a car-to-car calculation method according to the prior art.
2 is a view showing a vehicle danger area according to an embodiment of the present invention.
3 is a diagram illustrating a flow of a headway distance calculation method using a 3-channel camera according to an embodiment of the present invention.
4 is a flowchart illustrating a method of acquiring a side image and a front image using a half mirror according to an embodiment of the present invention.
5 is a flowchart illustrating a half mirror current control method according to an embodiment of the present invention.
FIG. 6 is a view illustrating a method of measuring a headway distance according to an embodiment of the present invention.
7 is a view showing a configuration of a half mirror according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an apparatus and various methods to which embodiments of the present invention are applied will be described in detail with reference to the drawings. The suffix "module" and " part "for the components used in the following description are given or mixed in consideration of ease of specification, and do not have their own meaning or role.

In the description of the embodiment, in the case of being described as being formed on the "upper or lower", "before" or "after" of each component, (Lower) "and" front or rear "encompass both that the two components are in direct contact with each other or that one or more other components are disposed between the two components.

In describing the components of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected to or connected to the other component, It should be understood that an element may be "connected," "coupled," or "connected."

It is also to be understood that the terms such as " comprises, "" comprising," or "having ", as used herein, mean that a component can be implanted unless specifically stated to the contrary. But should be construed as including other elements. All terms, including technical and scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. Commonly used terms, such as predefined terms, should be interpreted to be consistent with the contextual meanings of the related art, and are not to be construed as ideal or overly formal, unless expressly defined to the contrary.

2 is a view showing a vehicle danger area according to an embodiment of the present invention.

2, an apparatus for calculating an inter-vehicle distance using a three-channel camera may include a front camera 110, a first camera 120 and a second camera 130, and a processor 200. [

The front camera 110 may output a forward image of the vehicle. The front camera may be a single camera. The front camera 110 may have an area ranging from 0 degrees to 190 degrees as a measurement area.

The first camera 120 may include a half mirror 400. The first camera 120 may output the forward image of the vehicle and the left image of the vehicle based on the control of the half mirror 400. [ The one camera 120 may be disposed on the first side of the vehicle. For example, the first camera 120 may be disposed on the left side from the front direction of the vehicle.

The second camera 130 may include a half mirror 400. The first camera 120 can output a forward image of the vehicle and a right image of the vehicle based on the control of the half mirror 400. [ The two cameras 130 may be located on the second side of the vehicle. For example, the second camera 130 may be disposed on the right side from the front direction of the vehicle.

The processor 200 can recognize the area of the preceding vehicle from the image received from the front camera 110. [

For example, the processor 200 may recognize that the first forward vehicle 310 is located within 45 degrees to 145 degrees of the measurement area of the front camera.

For example, the processor 200 may recognize that the second front vehicle 320 is located within the 0 to 45 degree region of the measurement area of the front camera.

For example, the processor 200 may recognize that the third forward vehicle 330 is located within 145 degrees to 190 degrees of the measurement area of the front camera.

The processor 200 may select a camera corresponding to the identified recognition area based on the area of the preceding vehicle.

For example, the processor 200 may select the first camera 120 and the front camera 110 when the first front vehicle 310 is located in an area where the measurement area is 0 degrees or 45 degrees. have.

For example, the processor 200 may select the first camera 120 and the second camera 130 when the second front vehicle 320 is located in an area where the measurement area is 45 degrees or 145 degrees. .

For example, the processor 200 can select the front camera 110 and the second camera 130 when the third forward vehicle 330 is located in an area where the measurement area is 145 degrees or 90 degrees. have.

The processor 200 can set feature points for the inter-vehicle distance when recognizing the front vehicle. At this time, the feature point is set to the center of the vehicle, and the inter-vehicle distance may be the distance from the center of the vehicle to the center of the front vehicle.

The processor 200 can measure the inter-vehicle distance based on the camera. The processor 200 may measure the headway distance using the triangulation method using the calibration and the coordinate value of the tolerance correction of the peripheral image providing apparatus to measure the inter-vehicle distance in the stereo format.

The processor 200 can control the current supplied to the half mirror 400 disposed in the camera installed on the first side and the second side of the vehicle. The processor 200 can control to supply the electric current to the half mirror 400 when measuring the headway distance. The processor 200 can control to repeatedly adjust the current supplied to the half mirror 400 so that the cameras installed on the first and second sides of the vehicle output frame-by-frame front and side images.

The processor 200 can receive the front and side images from the cameras installed on the first and second sides of the vehicle by adjusting the reflectance and transmittance of the half mirror 400. [ Referring to FIG. 7, the camera can photograph the front or the side of the vehicle according to the transmittance and the reflectance of the half mirror 400. Referring to FIG. 7, the photographing direction can be determined corresponding to the state of the half mirror 400. For example, when the reflectance of the half mirror 400 is 100%, the front image can be photographed. For example, when the transmittance of the half mirror 400 is 100%, a lateral image can be photographed.

The processor 200 can utilize the forward and side images input from the cameras installed on the first and second sides of the vehicle as the corresponding image stereo vision.

The processor 200 can utilize the side image of the camera image as the top view and the dead zone detection system information of the peripheral image providing apparatus.

The processor 200 can utilize the forward image of the camera images installed on the first side and the second side of the vehicle as a three-channel camera.

3 is a diagram illustrating a flow of a headway distance calculation method using a 3-channel camera according to an embodiment of the present invention.

Referring to FIG. 3, the processor 200 may receive side and front images using the half mirror 400 added to the camera during operation (S210).

The processor 200 may recognize the forward vehicle based on the image received from the forward camera (S220). At this time, the measurement area of the front camera may be 0 to 190 degrees.

The processor 200 may determine whether the vehicle has been recognized within the range of 45 to 145 degrees of the measurement area (S230).

If the step S230 is satisfied, the processor 200 can select the camera installed on the first side and the second side of the vehicle (S235). Thereafter, the processor 200 may measure the inter-vehicle distance using the triangulation method based on the cameras installed on the first side and the second side of the vehicle (S260). The processor 200 may provide the measured inter-vehicle distance to the driver's equipment (S270).

If the step S230 is not satisfied, the processor 200 may determine whether the vehicle has been recognized in the range of 45 to 145 degrees of the measurement area (S240).

If the step S240 is satisfied, the processor 200 may select the first camera 120 and the front camera 110 (S245). Thereafter, the processor 200 may measure the inter-vehicle distance using the triangulation method based on the first camera 120 and the front camera 110 (S260). The processor 200 may provide the measured inter-vehicle distance to the driver's equipment (S270).

If the step S240 is not satisfied, the processor 200 may determine whether the vehicle has been recognized in the range of 45 to 145 degrees of the measurement area (S250).

If the step S250 is satisfied, the processor 200 can select the second camera 130 and the front camera 110 (S260). Thereafter, the processor 200 may measure the inter-vehicle distance using the triangulation method based on the second camera 130 and the front camera 110 (S260). The processor 200 may provide the measured inter-vehicle distance to the driver's equipment (S270).

If the step S250 is not satisfied, the step S220 may be performed again.

4 is a flowchart illustrating a method of acquiring a side image and a front image using a half mirror according to an embodiment of the present invention.

Referring to FIG. 4, the state of the vehicle may be IG On and D stage (S310).

At this time, the processor 200 may determine whether the vehicle is in the state of the front-vehicle distance measurement mode on the USM (S320).

If the step S320 is not satisfied, the processor 200 can maintain the state of the half mirror 400 installed in the camera in the current state (S325).

If the step S320 is satisfied, the processor 200 may activate the supply current to the half mirror 400 coupled to the left and right cameras of the peripheral image providing apparatus (S330).

Thereafter, the processor 200 may simultaneously input the front and side images of the left / right camera using the half mirror 400 (S340).

5 is a flowchart illustrating a half mirror current control method according to an embodiment of the present invention.

Referring to FIG. 5, when the supply current to the half mirror is activated, the processor 200 may control to supply current to the half mirror (S410).

After step S410, the processor 200 may repeatedly adjust the currents for the front and side image inputs of the input frame of the camera (S420).

After the step S420, the camera adjusts the reflectance and the transmittance of the half mirror 400 through the repeated adjustment to receive the front and side images of the vehicle (S430).

For example, if the camera receives an image of 60 frames per second using the frame in which the image is input, 30 frames can serve as a mirror by operating the reflectivity of the half mirror 400 to 100 percent. Thus, the camera can receive a forward image. In addition, in the remaining 30 frames, the transmittance of the half mirror 400 operates at 100 percent, so that the half mirror 400 serves as a general glass, thereby receiving a lateral image. That is, the camera can receive the front and side images in response to the adjustment of the reflectance and transmittance of the half mirror 400.

After step S430, the processor 200 receives the front and side images from the camera and can utilize the received image as a stereo vision (S440).

FIG. 6 is a view illustrating a method of measuring a headway distance according to an embodiment of the present invention.

Referring to FIG. 6, there is shown an inter-vehicle distance calculation when the front vehicle exists in the left area.

The processor 200 can obtain the coordinate information based on the camera image correction when the first front vehicle 310 is recognized.

The processor 200 may perform triangulation based on the coordinates of the pre-stored camera, the feature points of the first front vehicle 310, and the corrected coordinate information. The triangulation method may be a survey method for determining the plane position using the following equation for calculating the length of one side of a triangle and the length of one side after knowing the angle of both sides thereof.

The processor 200 may calculate the feature point of the first front vehicle 310 and the angle formed by the front camera 110 and the first camera 120 according to Equation (1) for the triangulation method measurement.

[Equation 1]

The angle of the point B (?) = 180 -? -?

At this time, the angle between the feature point of the first front vehicle 310 and the front camera may be?. The angle between the feature point of the front vehicle and the first camera 120 may be?. And? And? May be pre-stored information.

Then, the processor 200 can calculate the headway distance to the first front vehicle 310 by the following equation (2).

&Quot; (2) "

That is, α, γ, and AC lengths are pre-stored information, β is an angle of the point B, and BC is a distance from the front feature point to the first camera 120. At this time, the front camera may be disposed at the position of A. The first camera 120 may be disposed at the position of C That is, the distance between the front camera and the first camera 120 may be stored in advance.

The processor 200 may calculate the length AB based on Equation (2). The AB length may be an inter-vehicle distance from the preceding vehicle.

The method according to an embodiment of the present invention may be implemented as a program for execution on a computer and stored in a computer-readable recording medium. Examples of the computer-readable recording medium include a ROM, a RAM, a CD- Tape, floppy disk, optical data storage system, and the like. The computer readable recording medium may be distributed over a networked computer system so that computer readable code can be stored and executed in a distributed manner. And, functional program, code, and code segments for implementing the above-described method can be easily inferred by programmers in the technical field to which the embodiment belongs.

100: vehicle
110: front camera
120: First camera.
130: Second camera.
200: Processor
310, 320, 330:
400: half mirror

Claims (19)

The camera installed on the first side and the second side of the vehicle utilizes a half mirror to obtain side and front images;
Recognizing a forward vehicle based on a forward camera;
Identifying a recognized area of the recognized forward vehicle, and selecting a camera corresponding to the recognized area; And
And measuring an inter-vehicle distance based on the selected camera image. The method according to claim 1,
The steps of the camera installed on the first side and the second side of the vehicle utilizing the half mirror to obtain the side and front images
Determining whether the vehicle is in a running state, or in a forward vehicle-to-vehicle distance measuring mode;
Supplying current to the half mirror based on the supply current control in the case of the inter-vehicle distance measurement mode;
Activating a supply current of a half mirror disposed in the camera; And
Further comprising the step of the front and side images being received by the camera corresponding to the half mirror. 3. The method of claim 2,
A side image of the input camera image is utilized as a top view and a dead zone detection system information of a peripheral image providing apparatus; And
Using the forward image of the camera images installed on the first side and the second side of the vehicle as a three-channel camera; A method for calculating the headway distance using a 3 - channel camera that further includes. 3. The method of claim 2,
Wherein the step of inputting the front and side images by the camera corresponding to the half mirror
Supplying a current to the half mirror when the supply current of the half mirror is activated;
Repeatedly adjusting currents for the camera to input the front and side images for each frame;
Receiving the front and side images by adjusting reflectance and transmittance of the half mirror based on the adjusted current; And
And using the input front and side images as a corresponding image stereo vision. The method according to claim 1,
The step of recognizing the forward vehicle based on the forward camera
A method for calculating an inter-vehicle distance using a three-channel camera that recognizes a front vehicle based on the front camera having a measurement area of 0 to 190 degrees. 6. The method of claim 5,
The step of discriminating the recognition area of the recognized forward vehicle and the step of selecting the camera corresponding to the recognized recognition area
Measuring a headway distance based on the first camera and the front camera when the front vehicle is located in an area where the measurement area is at 0 degree and 45 degrees. 6. The method of claim 5,
The step of discriminating the recognition area of the recognized forward vehicle and the step of selecting the camera corresponding to the recognized recognition area
Further comprising the step of measuring an inter-vehicle distance based on the first camera and the second camera when the front vehicle is located in an area where the measurement area is 45 degrees to 145 degrees
A method of calculating the distance between two vehicles using a 3 - channel camera. 6. The method of claim 5,
The step of discriminating the recognition area of the recognized forward vehicle and the step of selecting the camera corresponding to the recognized recognition area
When the front vehicle is located in an area where the measurement area is 145 degrees to 190 degrees,
Further comprising the step of measuring an inter-vehicle distance based on the front camera and the second camera. The method according to claim 1,
The step of measuring the inter-vehicle distance based on the selected camera image
Obtaining coordinate information based on the camera image correction;
Performing triangulation based on the coordinates of the pre-stored camera and the feature points of the preceding vehicle; And
Further comprising the step of acquiring an inter-vehicle distance according to the triangulation method. A computer-readable recording medium on which a program for realizing a headway distance calculating method using a three-channel camera according to any one of claims 1 to 9 is recorded. A camera installed on the first side and the second side of the vehicle for obtaining side and front images utilizing a half mirror;
A front camera for recognizing a front vehicle;
A recognition unit for recognizing the recognition area of the recognized forward vehicle, a camera corresponding to the recognized recognition area,
And a processor for measuring an inter-vehicle distance based on the selected camera image. 12. The method of claim 11,
The processor
Vehicle distance measuring mode when the vehicle is in a running state,
A current is supplied to the half mirror based on the supply current control in the case of the inter-vehicle distance measurement mode,
Activating a supply current of the half mirror disposed in the camera,
And an inter-vehicle distance calculation device using a three-channel camera that receives front and side images from the camera corresponding to the half mirror. 13. The method of claim 12,
The processor
The side image of the input camera image is used as top view and blind zone detection system information of the peripheral image providing apparatus,
And the front image of the camera images installed on the first side and the second side of the vehicle is a 3-channel camera. 13. The method of claim 12,
The processor
Wherein when a supply current of the half mirror is activated, a current is supplied to the half mirror,
The camera repeatedly adjusts the current to input the front and side images for each frame,
Receiving the front and side images by adjusting reflectance and transmittance of the half mirror based on the adjusted current,
And using the received forward and side images as a corresponding image stereo vision
An apparatus for calculating distance between vehicles using a 3 - channel camera. 12. The method of claim 11,
The processor
An inter-vehicle distance calculating apparatus using a three-channel camera that recognizes a front vehicle based on the front camera having a measurement area of 0 to 190 degrees. 16. The method of claim 15,
The processor
And an inter-vehicle distance is measured based on the first camera and the front camera when the front vehicle is located in an area where the measurement area is at 0 degree and 45 degrees. 16. The method of claim 15,
The processor
When the front vehicle is located in an area where the measurement area is 45 degrees to 145 degrees, an inter-vehicle distance is measured based on the first camera and the second camera
An apparatus for calculating distance between vehicles using a 3 - channel camera. 16. The method of claim 15,
The processor
When the front vehicle is located in an area where the measurement area is 145 degrees to 190 degrees,
And an inter-vehicle distance is measured based on the front camera and the second camera
An apparatus for calculating distance between vehicles using a 3 - channel camera. 12. The method of claim 11,
The processor
Acquiring coordinate information based on the camera image correction,
The triangulation method is performed based on the coordinates of the previously stored camera and the feature points of the preceding vehicle,
An inter-vehicle distance calculation device using a three-channel camera for obtaining an inter-vehicle distance according to the triangulation method.

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