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.
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.
In one aspect of the invention, the illumination sources includes at least one light sources located on opposite sides of the camera.
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.
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.
Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings:
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.
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.
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.
The left light source 28a 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 28a. The camera 26 then captures that image and stores it in the memory 32. Next, as shown in
In one embodiment, the light sources 28a, 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 28a, 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.
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.
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.
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.
In one embodiment, the vehicle 18 (
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.
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.
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.