JP2004053523A - Inter-vehicle distance detection device - Google Patents

Abstract

To accurately calculate an inter-vehicle distance from a captured image without being affected by a change in a camera optical axis.
A vehicle detection unit detects a vehicle from an image captured by an imaging unit. The inter-vehicle distance calculation unit 80 uses the size ratio of the detected vehicle on the image captured this time and the image captured previously and the own vehicle speed detected by the speed detection unit 60, and the detected vehicle speed and the inter-vehicle distance as variables. The calculated inter-vehicle distance calculation line is calculated. Based on a predetermined number of inter-vehicle distance calculation straight lines calculated from a plurality of images at different imaging timings, voting is performed on a voting surface with the inter-vehicle distance and speed as axes, and the voting value is equal to or more than a predetermined value. Calculate the inter-vehicle distance and the detected vehicle speed from the position. Since the camera optical axis of the imaging unit 20 is not used as a parameter of the inter-vehicle distance calculation straight line, the inter-vehicle distance and the detected vehicle speed can be calculated without being affected by changes in the camera optical axis.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an inter-vehicle distance detecting device that detects an inter-vehicle distance between a host vehicle and a captured vehicle from a captured image around the host vehicle.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there is a device that detects a vehicle around a host vehicle during traveling, presents a positional relationship between the detected vehicle and the host vehicle to a driver or the like, or issues an alarm according to a vehicle interval from the host vehicle. In this method, a camera is mounted on a vehicle, and the presence or absence of a vehicle around the own vehicle and the distance from the own vehicle to the imaged vehicle are detected from an image captured by the camera.
[0003]
As a known technique for calculating a distance to a detected vehicle from an image captured by a camera mounted on the host vehicle, there is a method of calculating a distance from a captured image of a vehicle in a height direction. This is a camera attached to the vehicle in a predetermined direction so that the camera optical axis is horizontal to the ground, captures an image of the vehicle in a predetermined area, and measures the distance from the lowest end on the image to the ground contact position of the vehicle with the ground. The number b of pixels in the vertical direction is detected. Using a height h of the camera optical axis from the ground and the number of pixels a in the vertical direction on the captured image,
L = h / tan ((ab) / a)
Is detected.
[0004]
[Problems to be solved by the invention]
In the above-described conventional method, the camera optical axis and the ground need to be always horizontal, and the angle formed by the camera optical axis and the ground due to the weight balance of the occupant, changes in tire air pressure, acceleration, and the like. Has changed from the set value, there has been a problem that the distance to the vehicle in the predetermined area cannot be correctly detected.
[0005]
In view of such a conventional problem, the present invention provides an inter-vehicle distance detection device that can correctly detect an inter-vehicle distance from a captured image without being affected by a change in an angle between a camera optical axis and the ground. The purpose is to:
[0006]
[Means for Solving the Problems]
The present invention uses the vehicle speed and the inter-vehicle distance detected by the vehicle detection unit as variables, and compares the size ratio on the image of the vehicle detected from images at different imaging timings with the own vehicle speed detected by the speed detection unit. And calculates the inter-vehicle distance to the vehicle detected by the vehicle detection unit from the intersection of the inter-vehicle distance calculation straight lines calculated based on a plurality of images at different imaging timings. And
[0007]
【The invention's effect】
According to the present invention, the size ratio on the image of the vehicle detected from the images having different imaging timings and the own vehicle speed detected by the speed detection unit, and the speed and the headway of the vehicle detected by the vehicle detection unit as variables An inter-vehicle distance calculation straight line using the distance is calculated, and the inter-vehicle distance can be calculated from the intersection of the inter-vehicle distance calculation straight line and the inter-vehicle distance calculation straight line calculated from a plurality of images at different imaging timings. Since the optical axis of the camera as the imaging means is not used as a parameter when calculating the inter-vehicle distance in this manner, the inter-vehicle distance can be calculated from the captured image without being affected by a change in the angle between the camera optical axis and the ground. It can be calculated correctly.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described with reference to examples.
FIG. 1 is a block diagram showing the configuration of the present invention.
The timing signal generation unit 10 generates a timing signal of a time interval Δt that is a reference of processing timing of each unit, and converts the timing signal into an imaging unit 20, an image storage unit 30, a vehicle detection unit 40, a speed detection unit 60, an acceleration calculation unit 70 and the following distance calculation unit 80.
The imaging unit 20 captures an image of a road scene ahead of the vehicle using a video camera or the like attached to the vehicle in synchronization with a timing signal from the timing signal generation unit 10. The captured image is stored in an image storage unit 30 such as an image memory.
[0009]
The vehicle detection unit 40 detects a vehicle from the image captured by the imaging unit 20. As a vehicle detection method, for example, a method disclosed in Japanese Patent Application Laid-Open No. 8-320999 is used. This method detects the front vehicle by paying attention to the point at which the vertical edge detected on the side of the front vehicle is interrupted at the lowermost end of the vehicle and the objectivity which is a characteristic of the vehicle. Processing is performed to detect a vertical edge in the image, and a point where the vertical edge is interrupted is set as a vehicle bottom candidate. For example, when the right and left vehicle bottom candidates in the image are almost the same height, detection is performed. The object is determined to be a vehicle.
[0010]
When a vehicle is detected, the vehicle storage unit 50 assigns a number to the detected vehicle for identifying the vehicle, and stores the position and size (the number of pixels of the vehicle width [dot]) on the image. Also, the inter-vehicle distance and the vehicle speed between the host vehicle and the preceding vehicle obtained by the inter-vehicle distance calculation unit 80 described later are recorded.
The speed detector 60 detects the speed of the host vehicle. For example, the number of rotations of the wheel is counted at the time interval Δt, and the product of the number of rotations of the wheel and the outer peripheral length of the tire is obtained to obtain the vehicle speed.
[0011]
The acceleration calculator 70 calculates the acceleration by taking the difference between the speeds detected by the speed detector 60.
The inter-vehicle distance calculation unit 80 calculates the inter-vehicle distance L _n from the host vehicle to the preceding vehicle and the preceding vehicle speed _Vb .
[0012]
Hereinafter, a method of calculating the inter-vehicle distance L _n and the preceding vehicle velocity V _b at time n × Delta] t.
At time (n−1) × Δt, if the inter-vehicle distance between the preceding vehicle and the own vehicle and the preceding vehicle speed are not calculated by the inter-vehicle distance calculating unit 80, as shown in FIG. The speed of the host vehicle 1 at time n × Δt is V _an [m / s], and the speed of the front vehicle 2 at time n × Δt is V _bn [m / s]. If the inter-vehicle distance is L _n [m],
D _n = D _h × W / (2 × L _n × tan (θ / 2)) (1)
Is represented by Here, D _n is the number of pixels of the vehicle width [dot] in the captured image at time n × Δt, D _h is the number of pixels in the horizontal direction of the captured image [dot], W is the front vehicle width [m], and θ is the own vehicle. It is assumed that the angle of view [rad] of the image pickup unit 20 provided in 1 is set.
[0013]
Here, equation (1) holds at time (n−1) × Δt.
D _n-1 = D _h × W / (2 × L _n-1 × tan (θ / 2)) (2)
Can be represented by
When W is eliminated from the equations (1) and (2) to obtain the relationship between L _n-1 and L _n ,
_{D n × L n = D n} -1 × L n-1 (3)
It becomes.
[0014]
Here, the relationship between the inter-vehicle distances at the time (n−1) × Δt and the time n × Δt is obtained by using the relative speed between the own vehicle and the preceding vehicle.
_{L n = L n-1 -} (V an -V bn) × Δt (4)
Can be represented by
[0015]
Therefore, when L _n-1 is eliminated from the equations (3) and (4),
_{(D n / D n-1} -1) × L n = V an × Δt-V bn × Δt (5)
Is required.
V _an is known from the output from the speed detection unit 60, and D _n / D _n−1 is known because the number of pixels of the width of the front vehicle is calculated when the vehicle detection unit 40 detects the front vehicle. . Thus the formula (5) an inter-vehicle distance L _n, can be thought of as a straight line with a variable forward vehicle speed V _bn, the following formula (5) referred to as inter-vehicle distance calculating linear A _n.
[0016]
On the other hand, if the inter-vehicle distance between the preceding vehicle and the own vehicle and the speed of the preceding vehicle are calculated by the inter-vehicle distance calculation unit 80 at time (n-1) × Δt, the image is captured at time n × Δt. from the front vehicle width D _n in the captured image, and calculates the inter-vehicle distance L _n using equation (3), it is possible to calculate the preceding vehicle speed V _bn from equation (4) using the value.
Therefore, once the vehicle speed and the inter-vehicle distance of the preceding vehicle are calculated, the vehicle speed and the inter-vehicle distance of the preceding vehicle can be calculated using Expressions (3) and (4). it is not necessary to use a distance calculating linear a _n.
[0017]
When the own vehicle is accelerating and decelerating, as shown in FIG. 3, on the graph showing the inter-vehicle distance L between the own vehicle and the preceding vehicle on the horizontal axis and the preceding vehicle speed _Vb on the vertical axis, the time n × Δt vehicle speed obtained from the image captured at the time of the inter-vehicle distance and the calculated linear a _n, the time (n + 1) × Δt in the vehicle speed V _an, and D _{n /} D _n-1 obtained from the image captured at the time When obtaining an intersection X between inter-vehicle distance calculating linear _{a n + 1} in V _{an, + 1} and _{D n} + 1 / _{D n,} the preceding vehicle velocity _{V b} and the inter-vehicle distance L is determined.
[0018]
However, if the relative speed V _a -V _b = 0, the inter-vehicle distance L also changes, so the intersection X between the straight line _An and the straight line _{An + 1} moves each time imaging is performed. Closer to the host vehicle velocity V _a forward vehicle speed V _b, the smaller the amount of change in the inter-vehicle distance L per imaging times becomes the amount of movement of the linear A _n and the straight line A _{n + 1} the intersection of the X is small.
When such a vehicle is accelerated or decelerated, depicted on sequential graph vehicle distance calculating linear A _n of formula (5), by obtaining the intersection point X, the inter-vehicle distance and the preceding vehicle to the preceding vehicle Speed can be calculated.
[0019]
In fact, as shown in FIG. 4 split, inter-vehicle distance on the horizontal axis L, prepared voting plane with forward vehicle velocity V _b on the vertical axis, the forward vehicle speed [Delta] V _b width, the inter-vehicle distance to a block of ΔL width Then, the value of the distance L is increased from ΔL / 2 to the detection maximum distance L _{max in} increments of ΔL, and the value of _Vb is calculated from the inter-vehicle distance calculation straight line of Equation (5) with each L value. Voting is performed by adding +1 to a block including the numerical value of the distance L and the forward vehicle speed _Vb .
[0020]
If there is acceleration in the own vehicle, the distance between the vehicle and the vehicle in front always changes, and the distance between the line for calculating the distance between vehicles at the old time and the line for calculating the distance between vehicles at the current time is calculated to determine the distance between vehicles and the speed of the vehicle in front. Since the error is large even if it is calculated, the inter-vehicle distance calculation straight line used for the voting plane in FIG. Thus before performing the vote of inter-vehicle distance calculating linear A _n at time n × Delta] t, the time (n-m-1) subtracting the voting value of the inter-vehicle distance calculating linear A _n-m-1 of × Delta] t, namely - Do one.
[0021]
As described above, when voting is performed on the inter-vehicle distance calculation straight line portion on the voting plane shown in FIG. 4, the voting value of the portion where the intersections of the inter-vehicle distance calculation straight lines are concentrated increases. Then, the maximum value of the voting value on the voting surface is detected, and when the value becomes equal to or more than a predetermined threshold value, the forward vehicle speed and the following distance can be obtained from the position of the maximum voting value.
[0022]
In order to determine the inter-vehicle distance and the forward vehicle speed by the above method, the speed relationship between the own vehicle and the forward vehicle is, for example, when the own vehicle approaches the forward vehicle traveling at a constant speed from behind and decelerates. In the case where the vehicle is accelerated or decelerated so as to keep the inter-vehicle distance constant, the own vehicle needs to have acceleration. In the case of the former speed relationship, the calculation situation of the forward vehicle speed and the inter-vehicle distance will be described.
[0023]
As shown in FIG. 5 (a), the traveling vehicle ahead at a constant velocity V _b, from a state where the vehicle speed is traveling at a constant speed V _a1, the vehicle starts to decelerate at time t1 the same vehicle speed _{V b} to the preceding vehicle at time t2, the constant speed _{V a2} at time t3. As shown in this case acceleration of the host vehicle of FIG. 5 (b), until time t1 an acceleration 0, past the time t1 falls to acceleration -A _a. It takes _a constant value of the acceleration -Aa until near the time t3, then rises and the acceleration becomes 0 at the time t3.
The inter-vehicle distance between the host vehicle and the preceding vehicle has a bow shape that takes a minimum value at time t2 as shown in FIG. 5C.
[0024]
When the vehicle acceleration up to time t1 is 0, the inter-vehicle distance calculating straight line A _n calculated for each Δt front vehicle speed and the vehicle distance since the same line is not calculated. When acceleration occurs in the own vehicle from time t1, the calculation process of the forward vehicle speed and the inter-vehicle distance is started. However, since the relative speed between the own vehicle and the preceding vehicle is large, the inter-vehicle distance greatly changes every calculation. intersection of the inter-vehicle distance calculating linear a _n are not concentrated on one point. Intersection of the straight line A _n approaches the speed of the forward vehicle gradually began intensive, most concentrated in the vicinity of the time t2. After time t2, as the speed difference increases, the intersections gradually become less concentrated.
[0025]
Once the forward vehicle speed and the inter-vehicle distance are calculated, the inter-vehicle distance can be calculated by using the equation (3) from the change in the size of the forward vehicle on the image as described above. The vehicle speed ahead can be calculated by using the equation (4). Therefore, even when the own vehicle speed is constant and the forward vehicle speed and the inter-vehicle distance cannot be calculated using the voting surface as shown in FIG. 4, the vehicle speed and the inter-vehicle distance of the forward vehicle can always be calculated.
[0026]
The present embodiment is configured as described above, and the inter-vehicle distance calculation unit 80 uses the known size ratio of the preceding vehicle on the image and the own vehicle speed, and the inter-vehicle distance using the preceding vehicle speed and the inter-vehicle distance as variables. A distance calculation straight line is calculated. On the basis of the inter-vehicle distance calculation straight line and a predetermined number of inter-vehicle distance calculation lines calculated before this time, voting is performed at a position corresponding to the inter-vehicle distance calculation straight line on the voting plane with the inter-vehicle distance and the front vehicle speed as axes. Then, the inter-vehicle distance and the forward vehicle speed are calculated from the position where the voting value is equal to or more than the predetermined value. By using the inter-vehicle distance calculation straight line in this way, even if the vehicle tilts due to various factors and the optical axis of the imaging unit 20 including a camera or the like changes, the inter-vehicle distance to the detected vehicle and the detected vehicle speed Can be calculated.
[0027]
Further, once the inter-vehicle distance and the forward vehicle speed are calculated, the inter-vehicle distance and the forward vehicle speed can be calculated using Expressions (3) and (4). Even when it is not possible to calculate the inter-vehicle distance and the forward vehicle speed using Expression (5), the inter-vehicle distance and the forward vehicle speed can always be calculated.
[0028]
Further, when voting on the voting surface based on the inter-vehicle distance calculation line calculated this time, the inter-vehicle distance calculation line calculated a predetermined number of times ago from the inter-vehicle distance calculation line calculated based on the previously captured image. The voting value on the voting surface is updated by subtracting the value of the corresponding position on the voting surface. The inter-vehicle distance and the speed of the preceding vehicle are constantly changing. Even if the inter-vehicle distance and the forward vehicle speed are calculated based on the old inter-vehicle distance calculation straight line, there is a large error. By calculating the inter-vehicle distance and the forward vehicle speed using only the inter-vehicle distance calculation straight line calculated before, a new accurate value can always be calculated.
[0029]
As described above, the voting plane is updated by subtracting the voting value at the position corresponding to the predetermined inter-vehicle distance calculation straight line on the voting plane and voting at the position corresponding to the newly calculated inter-vehicle distance calculation straight line. By doing so, every time the inter-vehicle distance and the speed to the preceding vehicle are calculated, it is not necessary to vote at the position on the voting surface corresponding to the predetermined number of inter-vehicle distance calculation straight lines, and the amount of work at the time of calculation is reduced. it can.
The calculated inter-vehicle distance and the speed of the preceding vehicle are converted into a bird's-eye view of the surroundings of the host vehicle and displayed on the monitor of the driver's seat. Is improved.
[0030]
In the present embodiment, the imaging direction of the imaging unit 20 configured by a video camera or the like is set to the front of the host vehicle, but is not limited to this, and may be set to a predetermined direction such as the rear.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a diagram showing a positional relationship between a preceding vehicle and a host vehicle.
FIG. 3 is a graph centering on a forward vehicle speed and an inter-vehicle distance.
FIG. 4 is a diagram illustrating a voting surface on which voting is performed based on an inter-vehicle distance calculation straight line.
FIG. 5 is a diagram showing a traveling state of a host vehicle and a preceding vehicle.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 own vehicle 2 front vehicle 10 timing signal generation unit 20 imaging unit 30 image storage unit 40 vehicle detection unit 50 vehicle storage unit 60 speed detection unit 70 acceleration calculation unit 80 inter-vehicle distance calculation unit radar device

Claims (4)

A timing signal generator for instructing operation timing;
For each instruction from the timing signal generation unit, an imaging unit that images a road scene around the vehicle,
For each instruction from the timing signal generation unit, a speed detection unit that detects the vehicle speed,
A vehicle detection unit that detects the vehicle from the captured image and calculates the position and size of the detected vehicle;
A vehicle storage unit that stores the position and size of the vehicle detected by the vehicle detection unit;
An inter-vehicle distance calculation unit that calculates an inter-vehicle distance between the vehicle and the vehicle detected by the vehicle detection unit,
The inter-vehicle distance calculation unit uses the speed of the vehicle and the inter-vehicle distance detected by the vehicle detection unit as variables, and detects a size ratio on an image of the vehicle detected from images at different imaging timings and detects the size ratio on the speed detection unit. Calculating an inter-vehicle distance calculation straight line using the obtained own vehicle speed,
An inter-vehicle distance detection device that calculates an inter-vehicle distance to a vehicle detected by the vehicle detection unit from an intersection of inter-vehicle distance calculation straight lines calculated from a plurality of images at different imaging timings. The inter-vehicle distance calculation unit,
Using a voting surface with distance and speed as axes, voting is performed at a position on the voting surface corresponding to an inter-vehicle distance calculation straight line calculated from each of the plurality of images at different imaging timings, and the voting value is a predetermined value. The inter-vehicle distance detection device according to claim 1, wherein the inter-vehicle distance to the vehicle detected by the vehicle detection unit is calculated from the positions described above. The inter-vehicle distance calculation unit,
When voting at the position corresponding to the inter-vehicle distance calculation straight line on the voting surface, by invalidating the voting value at the position corresponding to the inter-vehicle distance calculation straight line calculated before a predetermined number of times, 3. The inter-vehicle distance detection device according to claim 2, wherein the voting value is updated, and the inter-vehicle distance to the vehicle detected by the vehicle detection unit is calculated. 4. The inter-vehicle distance calculation unit,
The inter-vehicle distance detection device according to claim 1, wherein the speed of the vehicle detected by the vehicle detection unit is calculated based on the inter-vehicle distance calculation straight line.

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