System for automated determination of retroreflectivity of road signs and other reflective objects

• US 6,674,878 B2
• Filed: 07/30/2001
• Issued: 01/06/2004
• Est. Priority Date: 06/07/2001
• Status: Active Grant

• Current Assignee: AMAC NORTH AMERICA, LLC
• Original Assignee: Facet Technology Corp.
• Inventors: Retterath, James E., Laumeyer, Robert A.
• Primary Examiner(s): Mehta, Bhavesh M.
• Assistant Examiner(s): Choobin, Barry
• Application Number:
  US09/918,375
• Publication Number:
  US 20020186865A1
• Time in Patent Office: 890 Days
• Field of Search: 382/104, 382/282, 382/274, 382/165, 382/100-105, 382/312, 340/907, 340/933, 340/904, 348/113, 345/581, 359/483, 700/225, 701/208, 405/82, 428/143, 235/471
• US Class Current: 382/104
• CPC Class Codes: G01N 2021/551 Retroreflectance
• CPC Class Codes: G01N 21/55 Specular reflectivity
• CPC Class Codes: G08G 1/0962 having an indicator mounted inside the vehicle, e.g. giving voice messages
• CPC Class Codes: G08G 1/096716 where the received information does not generate an automatic action on the vehicle control
• CPC Class Codes: G08G 1/096758 where no selection takes place on the transmitted or the received information
• CPC Class Codes: G08G 1/096775 where the origin of the information is a central station
• CPC Class Codes: G08G 1/096783 where the origin of the information is a roadside individual element
• CPC Class Codes: G08G 1/096791 where the origin of the information is another vehicle

Abstract

A system for the automated determination of retroreflectivity values for reflective surfaces disposed along a roadway repeatedly illuminates an area along the roadway that includes at least one reflective surface using a strobing light source. Multiple light intensity values are measured over a field of view which includes at least a portion of the area illuminated by the light source. A computer processing system is used to identifying a portion of the light intensity values associated with a reflective surface and analyze the portion of the light intensity values to determine at least one retroreflectivity value for that reflective surface. Preferably, color images of the area and locational information are also generated by the system and are used together with a characterization profile of the light source to enhance the accuracy of the determination of retroreflectivity values. In one embodiment, a three-dimensional overlay of retroreflectivity values for the roadway is generated and can be manipulated to display retroreflectivity values of a reflective surface at any desired point along the roadway. In another embodiment, a virtual drive through along a roadway is simulated using a plurality of retroreflectivity values to simulate reflections from each reflective surface disposed along the roadway during the virtual drive through.

Claims

1. A method of automated determination of retroreflectivity values for reflective surfaces disposed along a roadway comprising:

strobing a light source as the light source is traversed along the roadway to illuminate an area that includes at least one reflective surface;

collecting a plurality of light intensity measurements with at least one intensity sensor directed to cover a field of view which includes at least a portion of the area illuminated by the light source; and

using a computer processing system to;

identify a portion of at least one light intensity measurement associated with one of the at least one reflective surfaces; and

analyze the portion of the at least one light intensity measurement to determine at least one retroreflectivity value for that reflective surface.

2. The method of claim 1 further comprising:

creating a characterization profile for the light source, the characterization profile including an array of known luminance values of reflections of the light source; and

utilizing the characterization profile for the light source as part of determining the at least one retroreflectivity value for that reflective surface.

3. The method of claim 2 wherein the array of known luminance values of reflection comprises reflected intensity values for the light source over a range of colors and reflected intensity values over a range of relative angles between the light source and the reflective surface.

4. The method of claim 2 further comprising:

collecting a plurality of color images with at least one color camera directed to cover a field of view which includes at least a portion of the area illuminated byte light source; and

,

utilizing the characterization profile for the light source and the plurality of color images as part of determining the at least one retroreflectivity value for that reflective surface.

5. The method of claim 2 further comprising:

collecting locational information for each of the plurality of light intensity measurements;

using the computer processing system and the locational information to determine a coordinate location for each reflective surface; and

,

utilizing the characterization profile for the light source and the coordinate location as part of determining the at least one retroreflectivity value for that reflective surface.

6. The method of claim 1 further comprising:

creating a characterization profile for the intensity sensor, the characterization profile including an array of intensity values of reflections measured for a known light source; and

utilizing the characterization profile for the intensity sensor as part of determining the at least one retroreflectivity value for that reflective surface.

7. The method of claim 1 further comprising:

collecting locational information for each of the plurality of light intensity measurements,

using the computer processing system to analyze the locational information in order to correlate a plurality of retroreflectivity values that are common to one of the at least one reflective surfaces, each of the plurality of retroreflectivity values being associated with different locational information.

8. The method of claim 7 further comprising:

utilizing the locational information and the plurality of retroreflectivity values common to one of the reflected surfaces to create a three-dimensional plot of retroreflectivity values for that reflected surface.

9. The method of claim 8 wherein the three-dimensional plot of retroreflectivity values is created by interpolating retroreflectivity values based on the plurality of retroreflectivity values common to the one of the reflected surfaces.

10. The method of claim 9 further comprising:

determining a normal vector for a face of the reflective surface; and

,

assigning a common retroreflectivity value to discrete locations along each of at least two rays that are symmetrical in spacing relative to a normal vector of the reflective surface.

11. The method of claim 10 wherein the step of determining the normal vector utilizes a scanning laser system to determine the normal vector for the face of the reflective surface.

12. The method of claim 8 further comprising:

graphically displaying a depiction of the three-dimensional plot as a three dimensional overlay on a depiction of the roadway.

13. The method of claim 1 wherein the step of collecting the plurality of light intensity measurements records the light intensity measurements for processing by the computer processing system after the roadway has been traversed.

14. The method of claim 1 wherein each light intensity measurement comprises a frame of pixel intensity values and a plurality of reflective surfaces are present in at least one of the light intensity measurements.

15. The method of claim 1 wherein the step of strobing the light source is synchronized to the step of collecting the plurality of light intensity measurements.

16. The method of claim 1 wherein the step of strobing the light source is accomplished by alternatively strobing at least two high intensity strobe light systems mounted on a vehicle.

17. A method of automated determination of retroreflectivity values for reflective surfaces disposed along a roadway comprising:

strobing a light source as the light source is traversed along the roadway to illuminate an area that includes at least one reflective surface;

collecting a plurality of light intensity measurements with at least one intensity sensor without targeting a particular reflective surface; and

using a computer processing system to analyze the at least one light intensity measurement associated with one of the at least one reflective surfaces to determine at least one retroreflectivity value for that reflective surface.

18. The method of claim 17 wherein the light source is mounted on a vehicle that traverses the roadway at speeds approximately equal to posted speed limits for the roadway.

19. The method of claim 17 further comprising:

collecting locational information for each of the plurality of light intensity measurements; and

using the computer processing system to analyze the locational information and the at least one retroreflectivity value in order to compute a retroreflectivity value for any desired point along to roadway, including points not traversed byte light source.

20. A method of automated determination of retroreflectivity values for reflective surfaces disposed along a roadway comprising:

creating a characterization profile for a light source, the characterization profile including an array of known luminance values associated with reflections of the light source;

creating a characterization profile for an intensity sensor, the characterization profile including an array of intensity values measured for reflections of a known light source; and

using the light source to illuminate an area that includes at least one reflective surface as the light source is traversed along the roadway;

collecting a plurality of light intensity measurements with at least one intensity sensor without targeting a particular reflective surface;

collecting a plurality of color images with at least one color camera directed to cover a field of view which includes at least a portion of the area illuminated by the light source;

collecting locational information for at least each of the plurality of light intensity measurements;

using a computer processing system to determine at least one retroreflectivity value for one of the at least one reflective surfaces that reflective surface, including;

identifying a portion of at least one light intensity measurement associated with one of the at least one reflective surfaces;

utilizing the locational information to determine a location of the light source for that light intensity measurement and a location of that reflective surface;

utilizing at least one of the plurality of color images to identify at least one color associated with that reflective surface;

utilizing the characterization profile of the light source and the characterization profile for the intensity sensor to determine a luminance value associated with the portion of that light intensity measurement associated with that reflective surface based on the location of the light source for that light intensity measurement, the location of that reflective source and the at least one color associated with that reflective surface; and

converting the luminance value to a retroreflectivity value.

21. The method of claim 20 wherein each light intensity measurement comprises a frame of pixel intensity values and wherein the step of identifying the portion of at least one light intensity measurement is accomplished by analyzing at least one of the color images to determine the presence of a traffic control device in a portion of the color image and correlating the portion of the color image to a corresponding light intensity measurement to identify the portion of the frame of pixel intensity values associated with that traffic control device.

22. A system for acquiring information to assess reflective surfaces disposed along a roadway comprising:

a vehicle having;

at least one high output light source;

at least one intensity sensor;

at least one color camera;

a positioning system; and

a control system operably connected to the light source, intensity sensor, color camera and positioning system such that the intensity sensor, color camera and positioning system record information associated with an area that includes at least one reflective surface as the vehicle traverses along the roadway in response to repeated illumination of the area by the light source; and

a computer processing system that utilizes the recorded information to determine at least one retroreflectivity value for the at least one reflective surface.

23. The system of claim 22 further wherein the vehicle further comprises:

a laser scanning system that records distance information including at least a distance between the vehicle and each of the at least one reflective surfaces,

wherein the computer processing system utilizes the distance information to determine a normal vector for a face of the reflective surface.

24. The system of claim 22 wherein the at least one high output light source comprises at least two strobe lights arranged to alternatively illuminate the area at an effective strobe rate of at least one flash per second.

25. The system of claim 22 wherein the at least one intensity sensor comprises a black and white camera.

26. The system of claim 22 wherein the at least one color camera comprises a pair of digital color cameras mounted on the vehicle to generate stereoscopic images of the area.

27. The system of claim 22 wherein the positioning system comprises a global positioning system.

28. The system of claim 27 wherein the positioning system further comprises an inertial navigation system.

29. The system of claim 22 wherein at least a portion of the control system is implemented using the computer processing system.

30. A system for automated determination of retroreflectivity values for reflective surfaces disposed along a roadway comprising:

means for repeatedly illuminating an area that includes at least one reflective surface;

means for repeatedly measuring light intensity values over a field of view which includes at least a portion of the area illuminated by the light source; and

at least one computer processing system, including

means for identifying a portion of the light intensity values associated with one of the at least one reflective surfaces;

means for analyzing the portion of the light intensity values to determine at least one retroreflectivity value for that reflective surface;

means for recording color images of the area; and

means for generating locational information,

wherein the means for analyzing utilizes the color images and the locational information as part of determining the at least retroreflectivity value for that reflective surface.

31. The system of claim 30 wherein the means for repeatedly illuminating includes a source of illumination selected from the set consisting of:

an incandescent-based source of illumination, a halogen-based source of illumination, a fluorescent-based source of illumination, high intensity discharge type source of illumination, a xenon gas-based source of illumination, a single filament sealed-beam source of illumination, light emitting diodes or a dual filament source of sealed beam illumination.

32. The system of claim 30 wherein the light intensity values are pixel intensity values and the means for repeatedly measuring light intensity values comprises a black and white camera that generates a frame of pixel intensity values.

33. A method of automated determination of retroreflectivity values for reflective surfaces disposed along a roadway comprising:

illuminating an area along the roadway that includes at least one reflective surface with a light source without targeting the at least one reflective surface with the light source;

measuring light intensity values over a field of view which includes at least a potion of the area illuminated by the light source; and

using a computer processing system to;

identify a portion of the light intensity values associated with one of the at least one reflective surfaces; and

analyze the portion of the light intensity values to determine at least one retroreflectivity value for that reflective surface.

34. The method of claim 33 further comprising:

recording color images of the area;

generating locational information; and

utilizing the color images and the locational information as part of determining the at least one retroreflectivity value for that reflective surface.

35. The system of claim 33 wherein the light intensity values are pixel intensity values and the means for repeatedly measuring light intensity values comprises a black and white camera that generates a frame of pixel intensity values.