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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for monitoring the surroundings of a running vehicle and a vehicle-mounted apparatus for carrying out the method, including a camera and a laser radar for detection of vehicles on the road and in the lane
of the vehicle. The present invention also relates to a method for judging failure of the monitoring apparatus by detection of coincidence between the optical axes of the camera and the laser radar.
The instant application is based on Japanese Patent Application No. HEI 7-300214, filed Nov. 17, 1995, which is incorporated herein by reference for all purposes.
2. Brief Description of Related Art
As one of the conventional apparatuses of this type, Japanese Laid-Open Patent Publication (unexamined) No. 113482/1993 discloses a vehicle-mounted rear-end collision preventing apparatus. In this conventional apparatus, a laser radar of a
single beam type, from which a laser beam is emitted in one direction in a defined narrow range ahead of a vehicle, is associated with an image processing means, whereby an obstacle ahead in the vehicle's own traffic lane is detected.
An object of this conventional apparatus is to detect an obstacle in the vehicle's own lane. However, if the road is curved ahead of the vehicle, the laser beam emitted from the vehicle's laser radar does not irradiate the vehicle's own lane,
but irradiates an adjacent lane on either the left or the right side of the vehicle.
Accordingly, in case of a curved road, any obstacle ahead of the vehicle detected by the laser radar is not necessarily in the vehicle's own lane.
In view of the foregoing situation, in this conventional apparatus, first, an image ahead of a vehicle picked up by a camera is processed to detect the vehicle's own lane, and then the curvature ahead of the vehicle's own lane is detected. Then,
direction of beam irradiation from the laser radar is adjusted in conformity with the curvature, whereby the laser beam correctly irradiates the vehicle's own lane at all times even though the road is curved ahead of the vehicle.
However, only a laser radar of single beam type for emitting a laser beam in one direction in a defined narrow range is described in the mentioned conventional art.
For the purpose of monitoring the surroundings of a running vehicle over a wider range, several systems for causing a laser beam to scan a wider range in the horizontal direction have been heretofore proposed.
For example, Japanese Patent Publication (examined) No.6349/1986 discloses a vehicle-mounted obstacle detecting apparatus. In this apparatus, a laser beam emitted in the running direction of a vehicle performs a two-dimensional scan, and
reflected light from an obstacle is measured, whereby distance to the obstacle and the position thereof in the leftward or rightward direction are detected.
In the apparatus as disclosed in this Japanese patent publication, since it is intended to monitor not only the vehicle's own lane but also adjacent lanes over a wide range, it is possible to detect not only any obstacle in the vehicle's adjacent
lanes but also any obstacle in other lanes further away from the vehicle.
In such a detection system there still remains the following problem. In a laser radar of the beam-scan type, since not only other vehicles running ahead in the vehicle's own lane but also other vehicles running in other lanes, including
adjacent lanes, may be detected, it is absolutely essential to identify which of these vehicles represents an actual obstruction.
If the road is straight any other vehicle in the vehicle's own lane is running in front of the vehicle at all times. In this case, identification of another vehicle running ahead in the vehicle's own lane is very easy.
However, in reality no road is straight everywhere. On an ordinary road, another vehicle running ahead in a vehicle's own lane is not always in front of the vehicle. For example, where the road is curved rightward ahead of the vehicle, the
other vehicle running ahead in the vehicle's own lane is on the right side of the vehicle.
On the other hand, where the road is curved leftward ahead of the vehicle, the other vehicle running ahead in the vehicle's own lane is on left side of the vehicle.
Moreover, depending upon the type of curve, there may be a case where another vehicle running in an adjacent lane is actually in front of the equipped vehicle.
Accordingly, with respect to a beam-scan type laser radar, it is certain that obstacles may be detected over a wider range, but it is difficult to judge what is a true obstacle in the vehicle's own lane.
Japanese Laid-Open Patent Publication (unexamined) No. 113482/1993 discloses a vehicle-mounted rear-end collision preventing apparatus in which the irradiation range of the laser beam is fixed. This allows for any obstacle ahead in the vehicle's
own lane to be identified within a fixed range. In this apparatus, however, only an obstacle in the vehicle's own lane can be detected. Thus, the capability of the beam-scan type laser beam to monitor a wide range is not sufficiently utilized.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a surroundings monitoring method for monitoring the surroundings of a vehicle which is capable of identifying a detected object lying or running in a vehicle's own lane even when
employing a laser radar of the beam-scan type, and a surroundings monitoring apparatus to carry out this method.
It is a further object of the invention to provide a failure judgment method for judging a failure of the mentioned surroundings monitoring apparatus. This failure judgement method uses the lack of coincidence of the optical axes of a laser
radar beam, which is used to detect another vehicle, and a camera, which is used to detect the lane, in order to determine when a failure has occurred.
The surroundings monitoring method for monitoring the surroundings of a vehicle in accordance with the present invention comprises the steps of: (1) detecting image signals of a lane in which the vehicle is located with a camera mounted on the
vehicle; (2) determining coordinates of the lane on a display image by processing the image signals; (3) detecting an object ahead of the vehicle with a beam-scan type laser radar the center of whose optical axes are coincident with the optical axes of
the camera; transforming coordinates of the detected object in conformity with coordinate axes on the display image; and (5) judging whether the detected object is within the lane of the vehicle by comparing the transformed coordinates with the
coordinates of the lane.
In the above-mentioned method, first, the axes of the beam-scan type laser radar and the axes of the camera are preliminarily coincided with each other. The camera picks up an image of the road lying ahead of the vehicle, and processes the image
signals to detect the vehicle's own lane. The laser radar detects a distance and a direction from the vehicle to the detected object.
The distance and direction represent positional data of the detected object, which are then subject to a coordinate transformation to acknowledge the position on the image picked up by the camera. The coordinates of the detected object after the
coordinate transformation are then compared with the coordinates of the vehicle's own lane on the display image picked up by the camera.
If the detected object is within the scope of the coordinates indicating the vehicle's own lane, it is judged that the detected object is within the vehicle's own lane. On the other hand, if the detected object is outside the scope of the
coordinates indicating the vehicle's own lane, it is judged that the detected object is not an object within the vehicle's own lane.
The surroundings monitoring apparatus for carrying out the surroundings monitoring method in accordance with the invention comprises: (1) a camera having an optical axis, the camera being mounted on the vehicle for detecting an image of a road;
(2) a lane detecting means for detecting coordinates of a lane wherein the vehicle is located by processing image signals output from the camera onto a display image having coordinate axes; (3) a beam-scan type laser radar mounted on the vehicle and
installed such that an optical axis center thereof is coincident with the optical axis of the camera; (4) a coordinate transforming means for transforming the coordinates of an object detected by the laser radar in conformity with the coordinate axes of
the display image to provide transformed coordinates; and (5) a forward vehicle detecting means for separating objects detected within the lane from objects detected outside the lane by comparing the transformed coordinates with the coordinates of the
lane.
In the apparatus of above construction, the image of the road picked up by the camera is processed by the lane detecting means, whereby the vehicle's own lane is detected. The laser radar of the beam-scan type whose optical axes are coincident
with that of the camera performs a scan with a laser beam and detects a distance and a direction from the driver's vehicle to the detected object. Such positional information as distance and direction to the detected object is provided to the coordinate
transforming means and transformed to positional information of the coordinates on the display image of the camera.
In the forward vehicle detecting means (or separating means), the positional information of the vehicle's own lane indicated in the coordinates of the display image of the camera is compared with the positional information of the detected object. As a result of the comparison, a detected object existing within the vehicle's own lane is separated or distinguished from another detected object not existing within the vehicle's own lane.
In one preferred embodiment, the surroundings monitoring apparatus further comprises a representative coordinate computing means for computing representative coordinates of the objects detected by the laser radar, so that the representative
coordinates computed by the representative coordinate computing means are transformed in conformity with coordinate axes on the display image.
Normally, when detecting another vehicle as a detected object, the detection takes place at plural points and not at a single point. Accordingly, it is rather complicated and troublesome to compare all of the plural detected points with the
vehicle's own lane on the display image, and moreover the computing speed is reduced. In the preferred embodiment proposed herein, however, all of the plural detected points are integrally treated by a representative point, resulting in simpler
computations.
The failure judging method for judging a failure of the surroundings monitoring apparatus caused by misalignment between the laser radar and the camera comprises the steps of: (1) computing representative coordinates of another vehicle detected
by the laser radar; (2) transforming the representative coordinates in conformity with coordinate axes of a display image detected by the camera; (3) setting a window for designating a prescribed region on the basis of the transformed representative
coordinates of the other vehicle; (4) processing image signals in the window and judging whether or not the optical axes of the camera are coincident with the optical axes of the laser radar depending upon whether the other vehicle is within the window.
The failure judging method is to perform judgment of a failure of the surroundings monitoring apparatus provided with a laser radar and a camera whose optical axes are coincident with each other. First, the other vehicle existing in the vicinity
is detected by the laser radar. Then, the place where the other vehicle is picked up on the image of the camera is computed, and a prescribed region of the image which includes the other vehicle is established.
The image of the camera is then processed, and whether or not the optical axis of the camera is coincident with the optical axis of the laser radar is judged depending upon whether or not the vehicle is within the established prescribed region.
In other words, if the optical axes of the camera and that of the laser radar are coincident, the detected object picked up by the laser radar must be also picked up by the camera. On the other hand, if the detected object picked up by the laser radar
is not picked up by the camera, it may be judged that the optical axes are not coincident.
The failure judgment apparatus for judging a failure of the above-mentioned surroundings monitoring apparatus, to carry out the foregoing failure judging method comprises: (1) a camera having an optical axis, the camera being mounted on the
vehicle for picking up an image of a road; (2) a beam-scan type laser radar having an optical axis mounted on the vehicle and installed such that an optical axis center thereof is coincident with the optical axis of the camera; (3) a representative
coordinate computing means for computing representative coordinates of another vehicle detected by the laser radar; (4) a coordinate transforming means for transforming the representative coordinates in conformance with coordinate axes on a display image
of the camera; (5) a window setting means for setting a window for designating a prescribed region on the basis of the representative coordinates transformed by the coordinate transforming means; (6) an optical axis judging means for judging whether or
not the optical axis of the camera is coincident with the optical axis of the laser radar depending upon whether or not the other vehicle is within the window by processing image signals in the window.
The optical axis judging means determines whether the object to be detected is within the window by comparing the transformed representative coordinates with histograms of the detected outline. This function determines whether the optical axes
of the camera and the laser beam are coincident.
The optical axis judging means comprises a histogram computing means, a comparative reference value setting means, and a comparing means. The histogram computing means computes histograms representing the horizontal and vertical lines found
within the outline. The comparative reference value setting means sets comparative reference values based on the transformed coefficients. The comparing means compares the histograms with the comparative reference values based on the transformed
coefficients, and judges that the other vehicle is within the corrected window when the maximum value of the histogram is greater than the comparative reference value for a prescribed period of time.
It is to be noted that in the preferred embodiment proposed herein, the comparative reference value serving as a reference for judging the dimensions of the window set on the display image and for judging whether or not the vehicle exists is
corrected corresponding to the distance to the other vehicle detected by the laser radar. Accordingly, even if the distance to the vehicle detected by the laser radar varies, coincidence or non-coincidence between the optical axes of the camera and
laser radar is accurately judged.
In another preferred embodiment, the failure judging apparatus further comprises an optical axis judgment inhibiting means. This device inhibits the judgment of coincidence or non-coincidence between the optical axes of the camera and laser
radar when the distance indicated by the representative coordinates detected by the laser radar is over a prescribed distance. More specifically, the dimensions of the window and value of the comparative reference are corrected corresponding to the
distance to the other vehicle detected by the laser radar. When the distance to the other vehicle is excessively large, the image of the other vehicle on the display of the camera is excessively small, making it difficult to judge whether or not it is
an image of another vehicle. Accordingly, the result of coincidence judgment obtained is not always reliable.
Therefore, in the preferred embodiment proposed herein, it is established that the judgment of coincidence of the optical axes is inhibited if the distance to the other vehicle detected by the laser radar is over a prescribed distance.
Other objects, features and advantages of the invention will become apparent in the course of the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
In the detailed description of the preferred embodiment of the present invention presented below, reference is made to the accompanying drawings, in which:
FIG. 1 is an explanatory view showing a vehicle mounted with apparatus proposed by several embodiments of the present invention;
FIG. 2 is a block diagram showing an arrangement of a first preferred embodiment;
FIG. 3 shows an image of a road lying ahead picked up by a CCD camera mounted on the vehicle;
FIGS. 4(a), 4(b) and 4(c) are explanatory views showing positional information of a vehicle running ahead in respective coordinate systems;
FIG. 5 is an explanatory view showing a manner of detecting a vehicle running ahead by a laser radar mounted on the vehicle;
FIG. 6 is an explanatory view showing a manner of detecting a vehicle running ahead by the CCD camera mounted on the vehicle;
FIG. 7 is an explanatory view showing a manner of transforming positional information of an object detected by the laser radar in conformity with the coordinates on the display image;
FIG. 8 is a block diagram showing an arrangement of a second preferred embodiment;
FIGS. 9(a) and 9(b) are explanatory views to explain the operation of the representative coordinates computing means, where FIG. 9(a) is an explanatory view showing a manner of getting plural positional information using a laser radar from a
vehicle running ahead, and FIG. 9(b) is an explanatory view showing a manner of integrating the plural positional information into one representative point;
FIG. 10 is a block diagram showing an arrangement of a third preferred embodiment;
FIG. 11 is a block diagram showing a preferred arrangement of the optical axes non-coincidence detecting means employed in the third preferred embodiment; and
FIGS. 12(a) and 12(b) are explanatory views to explain the operation of the third preferred embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Several preferred embodiments in accordance with the present invention are hereinafter described with reference to the drawings.
The first preferred embodiment proposes a surroundings monitoring method for monitoring the surroundings of a vehicle to judge whether or not an object detected by a beam-scan type laser radar is within a vehicle's own lane, and in addition a
surroundings monitoring apparatus to carry out such a method.
The surroundings monitoring method is performed by the following steps.
First, image signals are detected by a camera mounted on a vehicle, directed in the direction of motion of the vehicle. The camera picks up and processes white lines drawn on the road surface ahead of the vehicle. Since the camera is mounted on
the vehicle, the camera is within the vehicle's own lane, from which the situation ahead is picked up.
Accordingly, a white line on the left side of the vehicle's own lane comes out on the left side of the image picked up by the camera, while a white line on the right side of the vehicle's own lane comes out on the right side of the image. The
white lines are normally drawn on the road so as to be very bright as compared with the road surface.
In the subsequent image processing, points of great brightness on the road are detected, and those points are recognized as a white line. The position of such a white line is indicated on H-V coordinate axes, where the V axis indicates the
vertical direction of the image, while the H axis indicates the horizontal direction of the image.
That is, in the H-V coordinate plane, a vehicle's own lane is indicated in a range from a coordinate position of the left white line to a coordinate position of the right white line.
A laser radar mounted on the vehicle, whose optical axis center is coincident with an optical axis of the camera, monitors the surroundings of the vehicle by scanning horizontally with a laser beam. The positional information of a detected
object is obtained by an R-.theta. coordinate system, indicated by a distance to the detected object and an angle .theta., representing an angle between the direction of forward travel of the vehicle and the path indicated by the distance.
The positional information of the detected object indicated in the R-.theta. coordinate system is then transformed to the H-V coordinate system so that it can be compared with the white lines on the display image. The positional information of
the detected object transformed to the H-V coordinate system is then compared with the white line positions detected by the camera and indicated in the H-V coordinate system.
Thus, if the comparison of positional information of the object detected by the laser radar and the camera indicates that the object is within the scope of the coordinates indicating the vehicle's own lane, then the detected object is judged to
be within the vehicle's own lane. On the other hand, if the comparison of positional information of the object detected by the laser radar and the camera indicates that the object is outside of the scope of the coordinates indicating the vehicle's own
lane, then the detected object is judged to be outside of the vehicle's own lane.
The surroundings monitoring apparatus for carrying out the mentioned surroundings monitoring method is described below.
FIG. 1 is an explanatory view showing a vehicle provided with an apparatus in accordance with the first preferred embodiment. In FIG. 1, reference numeral 1 denotes the above-mentioned vehicle, numeral 2 denotes another vehicle, numeral 3
denotes a CCD camera mounted on an upper part of vehicle 1, which is directed in a forward direction, numeral 4 denotes a beam-scan type laser radar mounted on the vehicle 1 whose optical axis is coincident with that of the CCD camera 3, and numeral 5 is
a processor for receiving outputs from the CCD camera 3 and the laser radar 4.
FIG. 2 is a block diagram showing the arrangement of the surroundings monitoring apparatus. In FIG. 2, reference numeral 51 denotes the lane detecting means, which is connected to the CCD camera 3 and processes an image picked up by the CCD
camera 3 in order to detect a region of the vehicle's own lane.
Numeral 52 denotes a coordinate transforming means connected to the laser radar 4. The coordinate transforming means 52 receives positional information from the other vehicle 2, which is running ahead, and subjects the information detected by
the laser radar 4 and represented in the R-.theta. coordinate system into positional information in the H-V coordinate system. More specifically, the positional information indicated in the R-.theta. coordinate system represented by a distance from
the vehicle 1 and an angle .theta. (between a reference position and the position of the detected vehicle) is transformed into positional information indicated in the H-V coordinate system corresponding to the image picked up by the CCD camera 3. In
this regard, the reference position is in a direction coincident with the optical axis of the CCD camera 3, i.e., in the forward direction of the vehicle 1.
Numeral 53 denotes the forward vehicle detecting means for detecting the vehicle running ahead. The forward vehicle detecting means is connected to the lane detecting means 51 and to the coordinate transforming means 52. The forward vehicle
detecting means 53 compares the positional information of the vehicle's own lane, indicated on the H-V coordinate axes and received from the lane detecting means 51, with the information provided by the coordinate transforming means 52, which represents
the positional information of the other vehicle 2 running ahead and indicated in H-V coordinates. The forward vehicle detecting means judges whether the vehicle running ahead is in the same lane as the vehicle 1 and outputs a corresponding result.
The forward vehicle detecting means 53 includes separating means for separating or distinguishing between an object detected within the vehicle's own lane and an object detected outside the vehicle's own lane.
Operation of the first preferred embodiment is described below.
An image that shows a road surface lying ahead of vehicle 1 is obtained from the CCD camera 3, as shown in FIG. 3. In FIG. 3, reference numeral 6 denotes an image of the road ahead picked up by the CCD camera 3, numeral 61 denotes a left side
white line in the image, numeral 62 denotes a right side white line in the image, numeral 63 denotes a prescribed scanning line in the image, and numeral 64 denotes a video signal of the scanning line 63.
Usually, white lines are drawn on a road to show the boundary between the lanes of running traffic. The video signal representation of a white line has the characteristic of a high brightness level as compared with that of the surroundings, as
indicated by the video signal 64 in FIG. 3.
Accordingly, any white line may be extracted by detecting a region of high brightness level in comparison with the surroundings. In this manner, the coordinates of the left side white line 61 in the H-V coordinate system and those of the right
side white line 62 in the H-V coordinate system are both obtained.
Further, a region from the left side white line 61 to the right side white line 62 is detected as the vehicle's own lane. Such detection of the vehicle's own lane is carried out with respect to the entire image by sequentially renewing the
scanning line 63 from the lower side of the image to upper side of the image.
In addition, with respect to a white line having fragmentary portions like the right side white line 62 in the drawing, the positions of the omitted portions are determined by an interpolative computation with reference to the adjacent portions
where white lines are drawn.
The positional information of the other vehicle 2 running ahead is obtained from the laser radar 4. As a result, it is possible to compare the positional information of the vehicle's own lane, obtained as described above, with the positional
information of the other vehicle 2 running ahead, obtained from the laser radar 4.
Accordingly, it is possible to separate or distinguish between any other vehicle running ahead in the same lane as the detection vehicle and any other vehicle running ahead in a different lane.
However, since the positional information of the other vehicle 2 obtained by the laser radar 4 is given in the form of R-.theta. coordinates, which are different from the H-V coordinate system of the image 6, it is impossible to compare these
positional information items with one another.
This problem is hereinafter described in detail with reference to FIG. 4.
FIGS. 4(a), 4(b) and 4(c) are explanatory views showing the positional information of the vehicle 2 running ahead in respective coordinate systems. FIG. 4(a) shows positional information of vehicle 2 in the R-.theta. coordinates obtained by the
laser radar 4. FIG. 4(b) shows positional information of vehicle 2 and the white lines in H-V coordinates. FIG. 4(c) shows X-Y coordinates establishing the vehicle 1 as an origin, where the longitudinal direction of the vehicle 1 comprises the Y-axis
and the horizontal direction comprises the X-axis.
The X-Y coordinates are employed as coordinates for vehicle control. Positional information in terms of R-.theta. coordinates or H-V coordinates obtained by the laser radar 4 and the CCD camera 3 are utilized after being transformed to
positional information in X-Y coordinates.
For example, vehicle control such as the control of distance between cars to observe a proper distance therebetween, as between vehicles 1 and 2, is computed in X-Y coordinates.
As is explicit from FIGS. 4(a), 4(b), and 4(c), the positional information of vehicle 2 is provided by laser radar 4, given in the form of R-.theta. coordinates indicated by the distance between vehicles 1 and 2 and the angle .theta.,
representing an angle between a path from vehicle 1 to 2 and a reference direction.
On the other hand, the positional information of the left side white line 61 and the right side white line 62 obtained from the image 6 is indicated in the form of H-V coordinates in which the origin is located at top left of the image, the
H-axis lies horizontally through the origin, and the V-axis lies vertically through the origin.
Therefore, it is impossible to project the positional information of the laser radar 4 in the form of the R-.theta. coordinate system onto the image 6 without transformation.
In view of the foregoing, in the first preferred embodiment, the positional information of vehicle 2, running ahead of the detection vehicle, obtained by the laser radar 4 and provided in the form of R-.theta. coordinates, is first transformed
to X-Y coordinates and stored.
The positional information in X-Y coordinates is further transformed to positional information in the form of H-V coordinates, whereby the transformed positional information may be compared with the positional information on the white lines
obtained from the image 6 in the form of H-V coordinates.
Thus, in the forward vehicle detecting means 53, the positional information on the white lines obtained from the lane detecting means 51 in the form of H-V coordinates is compared with the positional information of vehicle 2 obtained from the
coordinate transforming means 52 in the form of H-V coordinates. Forward vehicle detecting means 52 judges whether or not the positional information of the vehicle 2 is within the scope of vehicle l's lane, as detected by the own lane detecting means
51. If the ahead-running vehicle 2 is within the scope of the vehicle's own lane, vehicle 2 is judged as being in the vehicle's own lane. On the other hand, if the vehicle 2 is outside the scope of the vehicle's own lane, vehicle 2 is judged as being
outside the vehicle's own lane. The result of judgment is then output.
In addition, the positional information of vehicle 2 in the form of X-Y coordinates stored in the coordinate transforming means 52 and the result of judgment of the forward vehicle detecting means 53 are supplied to a vehicle controller (not
shown in the figures) to be utilized for vehicular control.
The positional information of white lines on the H-V coordinates obtained from the image 6 is transformed to positional information in X-Y coordinates by the coordinate transforming means (not shown), and supplied to the vehicular controller (not
shown) to be utilized for vehicle control.
In this regard, the positional information in the form of R-.theta. coordinates obtained by the laser radar 4 is transformed to positional information in the form of X-Y coordinates and the transformed information is stored. This is because,
when transforming the positional information in the form of X-Y coordinates to positional information in the form of H-V coordinates, to be compared with the positional information on the white lines, and further transformed back to positional
information in the form of H-V coordinates to be utilized for vehicular control, the accuracy of the positional information is deteriorated. In particular, large errors may arise from transforming H-V coordinates to X-Y coordinates.
The steps of detecting the forward vehicle by the laser radar 4 and the CCD camera 3 and the manner of coordinate transformation of the detected positional information are hereinafter described more specifically.
FIG. 5 is an explanatory view showing a manner of detecting the forward vehicle using the laser radar 4 mounted on the vehicle 1. In the drawing, reference numeral 7 denotes the vehicle's own lane, numeral 8 denotes a lane adjacent to lane 7,
numeral 21 denotes a vehicle running ahead in the vehicle's own lane 7, numeral 22 denotes a forward vehicle in the adjacent lane 8, and numerals 9, 10 denote lanes for other vehicles running in the opposite direction.
The laser radar 4 of the beam-scan type mounted on the vehicle 1 performs forward irradiation causing a fine laser beam to scan from a prescribed starting point in the horizontal direction, sequentially from left to right with a specified period
and a specified angle increment. At this time, if there is anything reflective (e.g., a rear reflector on a forward vehicle) in the irradiating direction, the laser from is reflected therefrom and returned.
The laser radar 4 receives this reflected light, and the distance to the forward object is detected by measuring the propagation delay time from the irradiation to the receipt of reflected light. A direction .theta.A from the vehicle 1 is
detected on the basis of the ordinal number of the specific laser beam reflected, from among those emitted in the sequential scanning operation from the known starting point.
It is to be noted that there are stationary objects such as delineators (reflecting mirrors), signboards, etc. which reflect the laser beam in addition to other vehicles running ahead, and that it is necessary to omit those stationary objects for
the purpose of preventing erroneous detection.
For that purpose, the first embodiment utilizes the fact that every stationary object is "carried away" rearward at the same speed as the speed of vehicle 1. In other words, stationary objects appear to have constant speed in a direction
opposite to the detection vehicle. Thus, only the positional information a1, a2, b1 and b2 are extracted.
The positional information (R, .theta.A) in R-.theta. coordinates obtained in the above-mentioned manner is delivered to the coordinate transforming means 52. In the coordinate transforming means 52, the position (R, .theta.A) is transformed to
the position (x,y) in X-Y coordinates according to the following transformation expressions.
Specifically, the transformation expression from the R-.theta. coordinate system to the X-Y coordinate system is comprised of following expressions (1) and (2) as is obvious from FIG. 4:
Since the angle information .theta. obtained by the laser radar 4 is an angle from the reference position, the .theta.A is converted to an angle .theta. indicated in FIG. 4(a) for substitution in the above expressions (1) and (2).
The coordinate transforming means 52 further transforms the transformed position (x, y) to a positional (h, v) in H-V coordinates. A transformation expression for that purpose will be shown below.
FIG. 6 shows an explanatory view showing a relation between the CCD camera 3 and forward vehicle 2, where reference numeral 31 denotes a lens whose focal length is "f", and numeral 32 denotes a CCD image pickup element 32.
When a horizontal image forming position of vehicle 2 on the CCD image pickup element 32 is indicated as a distance "h" from the optical axis center of the CCD, the horizontal position "x" of vehicle 2 is obtained from expression (3) according to
the principle of triangulation.
Accordingly, when introducing the positional information (x, y) obtained by transforming the positional information (R, .theta.) of the R-.theta. coordinates in the above expressions (3) and (4), the positional information (h, v) of vehicle 2 is
obtained in H-V coordinates. The positional information of vehicle 2 is then provided from the coordinate transforming means 52 to the forward vehicle detecting means 53.
FIG. 7 represents an explanatory view showing the operation of the forward vehicle detecting means 53. This drawing shows the manner of superposing a result of detection of the reflectors of forward vehicles 21 and 22 (running ahead of the
detect vehicle), detected by the laser radar 4 on the forward image 6 picked up by the CCD camera 3, after transforming the result to H-V coordinates according to the mentioned coordinate transformation.
In FIG. 7, reference numerals a1 and a2 respectively indicate detection results for the vehicle 21 running ahead in the vehicle's own lane, which have been detected by the laser radar 4 and transformed to H-V coordinates, while numerals b1 and b2
respectively indicate detection results of the other vehicle 22 running ahead in the adjacent lane, which have been detected by the laser radar 4 and transformed to H-V coordinates.
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