The present invention relates to technical field of vehicle safety, the vehicle anti-collision early warning method more particularly to based on car plate cooperative target and monocular-camera.
Background technology
Vehicle anti-collision early warning system is that the vehicle intelligent system of spacing monitoring, early warning of knocking into the back, anti-collision warning, navigation feature is realized by sensor, computer image processing technology, is a key technology in the unmanned technology of intelligent automobile.The automotive license plate image that vehicle anti-collision early warning system can be shot according to video camera determines the relative distance and relative velocity between front vehicles and Current vehicle by monocular vision location technology.So as to carry out danger judgement, driver is reminded to make corresponding actions to avoid the collision of automobile in time.The research of the system location technology can aid in driver to judge, point out early warning, improve drive safety.Vehicle anti-collision early warning system passes through advance preventing; it is effectively protected the safety of pedestrian in driver and road environment; greatly reduce car crass; reduce the generation that economic loss avoids accident; therefore; it is the priority research areas of vehicle safety, is enhancing vehicle safety, reduces the necessary means of traffic accident.
The number of sensors that existing vehicle anti-collision early warning system is present is more, processing speed is slow, the problem of cost is high, the patent of invention proposes a kind of localization method based on car plate cooperative target and monocular-camera, and intends a kind of vehicle anti-collision early warning system based on monocular-camera of research and development on this basis.The mode processing speed of monocular vision is fast, low cost.Including two aspect problems, one is the car plate in identification and positioning image, and two are to determine the position of car plate and attitude.
For recognizing and positioning the car plate in image, first, front truck and license plate image are tentatively extracted from afterbody image using the method based on mathematical morphology, because car body angle is tilted, the interference of car light image, pseudo- car plate is removed using the method based on characters on license plate textural characteristics rim detection, current hull back image includes many billboards and notice board image, in order to remove the interference of the pseudo- image in this part, car plate type is recognized using the method based on color characteristic, last positioning licence plate region, extracts the frame and angle point of car plate.
Position and the attitude of car plate are determined using the monocular-camera localization method based on cooperative target for Second Problem.Car plate can provide four edges line as cooperative target, and just car plate can be positioned using rectangle cooperative target localization method.All car plates in the visual field are carried out with the profile of the classification each car plate of Simultaneous Extracting Image according to morphology, the length and width data according to known to every kind of car plate, position and attitude of the car plate under bodywork reference frame are calculated using the monocular-camera localization method based on linear feature.
The content of the invention
The technical problem to be solved in the present invention is, there is provided a kind of using the monocular visual positioning method based on car plate frame rectangular characteristic, the relative distance and relative velocity between Current vehicle and front vehicles can be accurately determined, processing speed is fast, the vehicle anti-collision early warning method of low cost.
The technical scheme of use is:
Vehicle anti-collision early warning method based on car plate cooperative target and monocular-camera, pass through the forward looking camera installed in automobile head, real IMAQ during the backsight camera of automobile tail, it is respectively used to position the relative position and speed and relative position and speed for positioning behind vehicle and this car of traveling ahead vehicle and this car, the IMAQ of two front-and rear-view video cameras works respectively with vision positioning system, the fore-aft vehicle location information and vehicle operation data obtained through intellectual analysis integrated system according to two video cameras of front-and rear-view is analyzed the safe condition of this car, alarm is provided to driver according to assessment result and advised, alarm form is sound, light, voice three-level is alarmed.
The above-mentioned vehicle anti-collision early warning method based on car plate cooperative target and monocular-camera, including position and the attitude for recognizing and positioning the car plate in image with determine car plate, by the use of the four edges line of car plate frame as cooperative target, monocular visual positioning method determines the relative distance and relative velocity between Current vehicle and forward and backward side's vehicle.
Above-mentioned forward looking camera method for early warning uses identical localization method with rear view camera method for early warning, the two autonomous working.
The present invention has the following advantages that compared with prior art:
1. positioning precision is high.Relative distance and relative velocity between Current vehicle and front vehicles can accurately be determined using the monocular visual positioning method based on car plate frame rectangular characteristic.
2. it is applied widely.The anti-collision prewarning apparatus for vehicle is used as beasurement base using car plate frame, car plate frame has unification of the motherland standard, all there is consistency under standard Structured environment or under non-standard structure environment, therefore the anti-collision prewarning apparatus for vehicle has wide range of applications, independent of track.
Embodiment
Vehicle anti-collision early warning method based on car plate cooperative target and monocular-camera, the anti-collision early warning structure composition is as shown in Figure 1.Vehicle anti-collision early warning system is by the forward looking camera installed in automobile head, the backsight camera of automobile tail, image capturing system and Vehicle positioning system, intellectual analysis integrated system composition.Forward looking camera is used for the relative position and speed for positioning traveling ahead vehicle and this car;Rear view camera is used for the relative position and speed for positioning behind vehicle and this car.The image capturing system of two front-and rear-view video cameras, vision positioning system independently work.The vehicle anti-collision early warning, using the vehicle anti-collision early warning method based on car plate cooperative target and monocular vision.Including position and the attitude both sides problem for recognizing and positioning the car plate in image with determine car plate.Include being accurately positioned license plate image region based on architectural feature, textural characteristics, color characteristic, and extracting the frame of license plate image using comprehensive characteristics.Car plate frame has unified yardstick.And car plate frame is the rectangle of standard.Use based on the monocular visual positioning method of car plate frame rectangular characteristic to determine the relative distance and relative velocity between Current vehicle and front vehicles in the invention.This method positioning precision is high, and real-time is good.The fore-aft vehicle location information and vehicle operation data obtained again through intellectual analysis integrated system according to front and rear two video cameras, driver's manipulation behavioral data is analyzed the safe condition of this car, manipulation behavior to driver may be estimated to the influence that security is produced, alarm is provided to driver finally according to assessment result and is advised, alarm form is sound, light, the alarm of voice three-level.
The operation principle of the present invention
As shown in Figure 2:If camera model is known to perspective projection model and the intrinsic parameter of video camera.If the four edges of car plate frame
Direction vector under world coordinate system is
,
.The coordinate that four edges intersect at four summits is
.Direction vector of the four edges under camera coordinate system be
.Four summits
Coordinate under camera coordinate system is
.The straight line that four edges are imaged under image coordinate system
Equation is
.Direction vector is
, the coordinate put on graph line is
.Four summits
The picture point under image coordinate system
Coordinate be
.Car plate frame side
Length be
.Orientation problem is to determine the rigid body translation between object coordinates system and camera coordinate system
。
Perspective projection model is by space line
And graph line
And video camera photocentre is tied to a plane, this plane is called to explain plane
.Assuming that perpendicular to explanation plane
Normal vector be
, then normal vector
With graph line
And graph line
On any point
With the line of photocentre
It is all vertical, therefore normal vector
It can be expressed as
Direction vector
With
Direction vector apposition.
Under world coordinate system, side
And side
It is parallel, side
And side
Parallel, by perspective projection consistency, under camera coordinate system, this property keeps constant.Normal vector
With explanation plane
On any straight line it is all vertical, therefore
Perpendicular to side
.Known side
And side
It is parallel, therefore can be derived from normal vector
Perpendicular to side
.Because normal vector
And side
Vertically, therefore side
Direction vector under camera coordinate system is equal to normal vector
And normal vector
Apposition.I.e.:
Similarly, side
Direction vector under camera coordinate system is equal to normal vector
And normal vector
Apposition.I.e.:
Assuming that there is one and side under object coordinates system
And side
All vertical straight line
, then straight line
Direction vector
Equal to side
And side
The apposition of direction vector under object coordinates system.I.e.:
Under camera coordinate system, straight line
And side
And side
Position relationship keep constant, its direction vector
Equal to side
And side
The apposition of direction vector under camera coordinate system.I.e.:
Known three sides
、
、
(They are not parallel to each other, also do not pass through the camera light heart)Direction vector under object coordinates system, and this direction vector of three straight lines under camera coordinate system is calculated, by Screw theory, it is easy to calculate the spin matrix between camera coordinate system and object coordinates system.
As Fig. 2 shows, point
、
With corresponding picture point
、
And video camera photocentre also constitutes a closing triangle
.
In, straight line
、
Direction vector, it is known that be respectively
、
.Assuming that straight line
With straight line
Between folder cosine of an angle be
, therefore obtain:
By formula(2)Obtain side
Direction vector, it is assumed that straight line
With side
Between folder cosine of an angle be
, obtain:
Under object coordinates system, 2 points
、
Distance be
, according to perspective projection consistency, under camera coordinate system, distance between two points value keeps constant.As Fig. 2 shows, point
、
With corresponding picture point
、
And video camera photocentre also constitutes a closing triangle
.
In, straight line
、
Direction vector known to.Respectively
、
.Side
Direction vector, it is known that
In, obtained using sine:
By formula(8), obtain:
Postulated point
Coordinate is under camera coordinate system
, here
It is unknown number, therefore, obtains:
By(10), obtain:
Car plate is located at the front of video camera, thereforeTake on the occasion of reasonable, obtain:
Calculating more than, is obtained a littleCoordinate under camera coordinate system, therefore, it is possible to determine translation matrix of the car plate relative to camera coordinate system, you can determine coordinate of the car plate in camera coordinate system.Because car plate and automobile position relation are determined, the position pass degree relation of video camera and automobile.Therefore system, it is known that can obtain the distance between Ben Che and other vehicles and angular relationship.