Abstract:
Systems and methods for performing edge detection on a surface. An example system includes a camera having a line of sight approximately perpendicular to a plane associated with a camera surface, one or more illumination sources having a line of sight that is less than perpendicular to the plane by a predefined threshold amount, and a processor in signal communication with the camera. The processor receives images generated by the camera, compares the received images, and determines an edge located within one or more of the captured images based on the comparison.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    With automated moving vehicles, there is a desire to provide navigation with regard to certain contiguous features, such as road edges, turf edges, curbing, etc. However, it is very difficult to reliably detect and track edge features using passive optical techniques due to large variation in edge contrast due to environmental conditions. 
       SUMMARY OF THE INVENTION 
       [0002]    The present invention provides systems and methods for performing edge detection on a surface. An example system includes a camera having a line of sight approximately perpendicular to a plane associated with the surface, one or more illumination sources having a line of sight that is less than perpendicular to the plane by a predefined threshold amount, and a processor in signal communication with the camera. The processor receives images generated by the camera, compares the received images, and determines an edge located within one or more of the captured images based on the comparison. 
         [0003]    In one aspect of the invention, the illumination sources includes at least one light sources located on opposite sides of the camera. 
         [0004]    In another aspect of the invention, the light sources are strobed relative to a frame rate of the camera and a predefined image capturing protocol. 
         [0005]    In still another aspect of the invention, the processor separates the received images from the camera into first images that are illuminated by a first one of the light sources and second images that are illuminated by a second one of the light sources. The processor compares one of the first images to one of the second images. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings: 
           [0007]      FIG. 1  illustrates a block diagram of a system formed in accordance with an embodiment of the present invention; and 
           [0008]      FIGS. 2-4  are side views of various side illumination techniques using the system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0009]      FIG. 1  illustrates a vehicle  18  that has an example system  20  configured to autonomously determine edges and use that information for controlling a vehicle. The system  20  includes at least a processor  24 , a camera  26 , one or more light sources  28 , vehicle control components  30  and memory  32 . The processor  24  is in signal communication with the memory  32 , the camera  26  and the vehicle control components  30  and may also be in signal communication with the light sources  28 . 
         [0010]    The camera  26  records images of a surface and sends the recorded images to the processor  24 . The one or more light sources  28  illuminate the surface based on a predefined protocol while the camera  26  is recording images. The processor  24  analyzes the recorded images to determine the location of an edge based on predefined threshold requirements. Edge detection information produced by the processor  24  is sent to the vehicle control components  30 . The vehicle control components  30  then navigate the vehicle  18  based on predefined navigation rules with regard to the detected edge. 
         [0011]    An example technique for using the system  20  or a portion of the system  20  (only one illumination source (light  28 ) includes continuously illuminating the edge in such a way as to create a strong shadow. The processor  24  uses edge detection processing to locate the illuminated edge. 
         [0012]    Another example technique includes alternately illuminating (i.e. strobe) from a first angle where a shadow caused by the edge is formed and an opposing second angle where no shadow is formed. The processor  24  detects the edge by taking a difference of image frames of the different light sources and setting a mid-point (or other value) threshold on the difference data. If the two light sources are of equal brightness, then the average luminance for the non-shadowed area will be nearly equal. Consequently, the difference in the non-shadowed area will be nearly zero while the difference in shadow-non-shadow area will be much larger. Other illumination and processing techniques may be used. 
         [0013]      FIGS. 2A , B illustrate an example of the layout of two side light sources  28   a, b  relative to the camera  26 . The exact angle at which the light sources  28   a, b  is adjustable depending upon the assumed heights and types of edges that are to be detected. In this example the light sources  28   a, b  are placed so that their line-of-sight (beam angle) is greater than 20° away from the line-of-sight (centerline) of the camera  26 . 
         [0014]    The left light source  28   a  is first illuminated onto a surface  40 , thereby exposing areas  42  and  44  of the surface  40 . A gap that is in the shadow between  42  and  44  is not illuminated by light emanating from the light source  28   a . The camera  26  then captures that image and stores it in the memory  32 . Next, as shown in  FIG. 3B , the left light source  28   a  is deactivated and the right light source  28   b  is activated, thereby illuminating the entire area  46  of the surface  40 . The camera  26  then obtains another image and stores it in the memory  32 . Then, the processor  24  compares the stored images to determine changes in various image qualities, such as chrominance or luminance. The processor  24  uses the determined changes in image qualities to perform edge detection. An edge is detected when a threshold number of proximate pairs (or other combinations) of pixels vary in predefined image quality by a threshold amount. Other edge detection techniques may be used on the result of the compared images. 
         [0015]    In one embodiment, the light sources  28   a, b  are strobbed at a predefined frequency relative to the frame rate of the camera  26  (video). For example, if a camera has a raw frame rate of 60 Hz and two light sources were used then the strobe frequency would be no higher than 30 Hz on each strobe light—one for alternate frames. The rate at which the edge needs to be examined depends on the speed of the vehicle, the linearity/dynamics of the edge being tracked, the dwell of the strobe, the ability of the vehicle to coast between edge observations, and other factors. In another embodiment, the light sources  28   a, b  are continuously illuminated or can be alternated with various other illumination schemes (such as strobbing), thereby allowing the processor  24  to analyze various illumination schemes upon a desired surface. 
         [0016]      FIG. 3  illustrates a surface  50  that includes a narrow channel  52  that is desired to be detected by the system  20 . In order to provide better illumination enhancement, the second light source  28   b  has a line-of-sight with an angular difference from the line-of-sight of the camera  26  that is less than 30°. The actual angle depends on the depth and width of the slot. It may be in the same plane as the camera  26  or greater than 30°. The angles of the light sources  28   a, b  relative to the camera  26  and the surface  50  are set in order to produce the best illumination results for increasing edge detection by the processor  24 . Also, 3 or more lights (a third light source  28   c ) may be needed to track the slot for left and right deviations depending on its depth/width ratio. 
         [0017]      FIG. 4  illustrates another application of the system  20  for use in determining a raised edge  58  on a surface  56 . Similar to the process described in  FIGS. 3A , B, the light sources  28   a, b  are alternately illuminated thereby allowing the camera  26  to capture various images with differently angled light sources in order to analyze, compare and determine if an edge (in this case raised edge) exists. 
         [0018]    In one embodiment of the invention, the light source  28  can be any of a number of visible illumination sources, such as fluorescent light, an incandescent light or xenon light. 
         [0019]    The light source  28  may also produce a non-visible illumination, such as light-emitting diodes (LEDs) for producing infrared light or laser diodes for producing a laser light beam. If a laser light source is used, then mechanisms may be included for scanning the laser beam in a desired pattern along a targeted surface. 
         [0020]    In other embodiments, more than two light sources may be used at a variety of other angles relative to the camera  26 . Also, in a low-light environment a single light source might be capable of producing an adequate shadow for allowing the processor  24  to detect an edge. Any combination of illumination sources may be used. Also, the illumination source may be restricted to a certain frequency range, such as when illumination in a specific color is desired. 
         [0021]    In one embodiment, the vehicle  18  ( FIG. 1 ) may be any of a variety of vehicles that would benefit from having improved edge detection capabilities, for example an automated lawn mower. The edge detection capabilities discussed above could be combined with other navigation systems, such as GPS, to provide a more comprehensive autonavigation system. 
         [0022]    If the form of the edge is fixed and known, steps up like a curb on the passenger side of a car, or steps down like the uncut-to-cut edge of turf, then the placement of the light sources and the location of the edge relative to the shadow pattern is also fixed. If the form of the edge is not fixed, the system combines some of the lighting patterns and techniques shown in the figures above to allow the system to deduce the form of the edge based on the contrast patterns produced when it is illuminated from different angles. 
         [0023]    If the ambient light is low or the frequency of the supplemental light can be filtered from the ambient light, processing the attained images to determine the edge is much more effective since the contrast between the shadow and illuminated surfaces will be greater. 
         [0024]    While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.