System for road sign sheeting classification

• US 20050249378A1
• Filed: 02/11/2005
• Published: 11/10/2005
• Est. Priority Date: 08/12/2000
• Status: Active Grant

• Current Assignee: Mandli Communications, Inc.
• Original Assignee: Facet Technologies LLC
• Inventors: Laumeyer, Robert A., Retterath, James E.
• Granted Patent: US 7,515,736 B2
• Time in Patent Office: Days
• US Class Current: 382/104
• CPC Class Codes: G01N 21/251 Colorimeters; Construction thereof
• CPC Class Codes: G01N 21/55 Specular reflectivity
• CPC Class Codes: G01N 21/84 Systems specially adapted for particular applications
• CPC Class Codes: G01N 2201/06113 Coherent sources; lasers
• CPC Class Codes: G01N 2201/102 Video camera
• CPC Class Codes: G01N 2201/12 Circuits of general importance; Signal processing
• CPC Class Codes: G01S 17/06 Systems determining position data of a target
• CPC Class Codes: G06V 20/56 exterior to a vehicle by using sensors mounted on the vehicle
• CPC Class Codes: G06V 20/582 of traffic signs
• CPC Class Codes: G08G 1/096758 where no selection takes place on the transmitted or the received information
• CPC Class Codes: G08G 1/096783 where the origin of the information is a roadside individual element

Abstract

A system for classifying different types of sheeting materials of road signs depicted in a videostream compares estimated retroreflectivity values against known minimum retroreflectivity values for each of a plurality of colors. Once a road sign has been identified in the videostream, the frames associated with that road sign are analyzed to determine each of a plurality of colors present on the road sign. An estimated retroreflectivity for each of the plurality of colors present on the road sign is then determined. By comparing the estimated retroreflectivity for each of the plurality of colors against known minimum retroreflectivity values for the corresponding color for different types of sheeting materials, an accurate determination of the classification of the sheeting material of the road sign is established. Preferably, certain conditions of gross failure of the sheeting material are filtered out before classification of the sheeting material is determined.

Claims

1. A method for determining sheeting type of a reflective sheeting material covering at least a portion of a surface of a road sign comprising:

using a light source to illuminate at least a portion of the reflective sheeting material covering the road sign as the light source is traversed along the roadway;

collecting a plurality of light intensity measurements reflected from the at least a portion of the reflective sheeting material to generate an as-measured retroreflectivity profile, the light intensity measurements corresponding to exemplary angular displacements of incident light from a reference position; and

determining sheeting type of the reflective sheeting material based on the as-measured retroreflectivity profile.

2. The method of claim 1, wherein determining sheeting type of the reflective sheeting material further comprises:

providing a database of retroreflectivity profiles, each retroreflectivity profile having an associated known sheeting type;

selecting a retroreflectivity profile from the retroreflectivity profile pool that best correlates to the as-measured retroreflectivity profile; and

determining sheeting type of the retroreflective sheeting material based on the retroreflectivity profile associated with the selected retroreflectivity profile.

3. The method of claim 2, wherein the known sheeting type is selected from the group consisting of Type I (Engineer Grade), Type III (High Intensity), and Type VII (Prismatic).

4. The method of claim 3, wherein the Prismatic is one of Type VIIa (Diamond Grade VIP) and Type VIIb (Diamond Grade LDP).

5. The method of claim 2, wherein the providing step comprises establishing a functional relationship between a plurality of exemplary instances of retroreflectivity values corresponding to each known sheeting type and a plurality of instances of one of an observation angle and an entrance angle.

6. The method of claim 2, wherein the retroreflectivity profile is a characteristic curve of retroreflectivity values represented as a function of one of a monotonically varying observation angle and an entrance angle.

7. The method of claim 2, wherein the as-measured retroreflectivity profile is a curve of retroreflectivity values calculated from the plurality of light intensity measurements plotted as a function of the exemplary angular displacements of incident light from a reference position.

8. The method of claim 7, wherein each of the exemplary angular displacements of incident light comprises an observation angle corresponding to one of a plurality of distances of the light source from the road sign.

9. The method of claim 7, wherein each of the exemplary angular displacements comprises an entrance angle corresponding to one of a plurality of distances of the road sign from the road sign.

10. The method of claim 7, wherein each of the exemplary angular displacements comprises an observation angle corresponding to one of a plurality of distances of the light source from the road sign.

11. The method of claim 2, wherein the selecting step comprises:

providing a computer model coding a function for obtaining a set of coordinates from each retroreflectivity profile, each coordinate comprising a pairing of a retroreflectivity value and an associated angular displacement, wherein the function associates the retroreflectivity value to the angular displacement;

applying the computer model to the retroreflectivity profiles in the retroreflectivity pool to generate a set of reference coordinates for each retroreflectivity profile, each set of reference coordinates defining a characteristic curve having a characteristic shape;

applying the computer model to the as-measured retroreflectivity profile to obtain a set of as-measured coordinates defining an as-measured performance curve having an as-measured shape; and

selecting the characteristic curve having the characteristic shape which best approximates the as-measured shape.

12. The method of claim 11, wherein the selecting step comprises:

computing parameters to provide a best-fit curve to the set of as-measured coordinates;

scaling the characteristic curves to obtain a scaled characteristic curve with a characteristic shape such that the scaled characteristic curve is sized substantially the same as the as-measured performance curve; and

selecting the characteristic curve as acceptable if a deviation of the characteristic shape from the as-measured shape is within a predefined threshold.

13. The method of claim 12, wherein scaling the characteristic curves comprises multiplying the set of reference coordinates for each retroreflectivity profile by a positive scaling factor less than unity to obtain a set of scaled reference coordinates defining a scaled characteristic curve having a characteristic shape.

14. The method of claim 2, wherein the determining step comprises the steps of:

calculating a degree of correlation between the as-measured retroreflectivity profile and the selected retroreflectivity profile;

selecting the sheeting type associated with the selected retroreflectivity profile if the degree of correlation lies between an acceptable range of predefined values; and

identifying the road sign as exhibiting a gross failure of the reflective sheeting material covering at least a portion of the surface of the road sign if the degree of correlation lies outside the acceptable range of predefined values.

15. A method for determining sheeting type of a reflective sheeting material covering a road sign comprising:

means for illuminating at least a portion of the reflective sheeting material covering the road sign from a plurality of distances along the roadway;

means for collecting a plurality of light intensity measurements reflected from the at least a portion of the reflective sheeting material;

means for generating an as-measured retroreflectivity profile using the light intensity measurements corresponding to exemplary angular displacements of incident light from a reference position;

means for providing a database of retroreflectivity profiles with each retroreflectivity profile having an associated known sheeting type;

means for comparing the as-measured profile to each retroreflectivity profile from the retroreflectivity profile pool;

means for selecting the retroreflectivity profile that best correlates to the as-measured retroreflectivity profile; and

means for determining sheeting type of the reflective sheeting material based on the known sheeting type associated with the selected retroreflectivity profile.

16. The method of claim 15, wherein the means for determining sheeting type further comprises:

means for calculating a degree of correlation between the as-measured retroreflectivity profile and the selected retroreflectivity profile;

means for determining if the degree of correlation lies between an acceptable range of predefined values;

means for selecting the sheeting type associated with the selected retroreflectivity profile if the degree of correlation lies between an acceptable range of predefined values; and

means for classifying the road sign as exhibiting a gross failure of the reflective sheeting material covering at least a portion of the surface of the road sign if the degree of correlation lies outside the acceptable range of predefined values.

17. The method of claim 15, wherein the means for determining sheeting type further comprises:

means for computing parameters to provide a best-fit curve to the as-measured retroreflectivity profile, the best-fit curve having an as-measured shape;

means for scaling each retroreflectivity profile in the retroreflectivity pool to obtain a scaled characteristic curve sized substantially the same as the best-fit curve and having a characteristic shape; and

means for computing a deviation of the characteristic shape from the as-measured shape;

means for determining the sheeting type by identifying the sheeting type associated with the characteristic curve if the deviation of the characteristic shape from the as-measured shape is within a predefined threshold; and

means for filtering the road sign as exhibiting a gross failure of the reflective sheeting material covering at least a portion of the surface of the road sign if the deviation lies outside the predefined threshold.

18. A system determining sheeting type of a reflective sheeting material covering a road sign comprising:

at least one light source mounted on a vehicle capable of traversing a roadway and suitable for illuminating at least a portion of the road sign;

at least one light intensity sensor for receiving light reflected from the road sign and computing the intensity of the received light;

a positioning system for determining a location of the vehicle from a stationary frame of reference;

a ranging system for determining a distance of the road sign from the light source and an inclination of a surface of the road sign relative to the light source;

a control system operably connected to the light source, intensity sensor, positioning system and ranging system such that the intensity sensor, ranging system and positioning system record information associated with an area that includes at least one road sign 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 an as-measured retroreflectivity profile having an as-measured shape and comprising the plurality of as-measured retroreflectivity values for the sheeting type of the road sign and comparing the as-measured shape with a characteristic shape of at least one known retroreflectivity profile in a database of known retroreflectivity profiles for each of a plurality of different sheeting types to classify a sheeting material of the road sign as one of the plurality of different sheeting types.

19. A method for classifying a road sign having sheeting types having at least one color, each sheeting type of a particular color covering at least one non-overlapping area of the road sign, the method comprising the steps of:

using a light source to illuminate at least a portion of the reflective sheeting material covering the road sign as the light source is traversed along the roadway;

collecting a plurality of light intensity measurements reflected from the at least a portion of the reflective sheeting material to generate an as-measured retroreflectivity profile, the light intensity measurements corresponding to exemplary angular displacements of incident light from a reference position;

providing a database of retroreflectivity profiles, each retroreflectivity profile having an associated known sheeting type having a known color;

providing a database of road signs, each road sign categorized according to a set of colors associated with each known sheeting type covering the road sign;

selecting at least one retroreflectivity profile from the retroreflectivity profile pool that best correlates to at least a portion of the as-measured retroreflectivity profile;

determining a set of sheeting types associated with the selected retroreflectivity profiles; and

classifying the road sign according to the set of colors associated with the set of selected sheeting types.