Retroreflectivity Measurement System Using Spectral Filtering
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Solution Overview
Problem
Existing retroreflectivity measurement systems face challenges in accurately assessing road markings under varying light conditions, particularly due to the impact of ambient light and strobe light sensitivity, which can lead to unreliable and inaccurate measurements.
Innovation Solution
A retroreflectivity measurement system mounted on a vehicle, equipped with a light source projecting light within a specific visible spectrum, a camera apparatus selectively sensitive to different portions of the spectrum to capture filtered images, and a controller that estimates ambient intensity using scaling factors to calculate retroreflectivity, allowing for reliable measurements without strobing illumination and minimizing the effects of ambient light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If strobe light is used to illuminate road markings for measurement, then measurement speed is improved, but reliability deteriorates due to strobe light sensitivity and inaccurate measurements
Solution Approach 1:
The patent uses continuous illumination with periodic filtering instead of strobe light. The camera captures images continuously while the controller periodically applies digital filters to isolate specific wavelength ranges, achieving both fast measurement speed and high reliability by eliminating strobe light sensitivity issues
Solution Approach 2:
The patent replaces the mechanical/optical strobe light system with a continuous illumination system combined with digital signal processing. Instead of using physical light modulation, the system uses software-based filtering to achieve temporal separation of signal components, improving reliability while maintaining measurement speed
2Ease of operation
If ambient light is included in measurement, then ease of operation is improved (no special lighting conditions needed), but measurement precision deteriorates due to light intensity variations
Solution Approach 1:
The patent segments the spectral information by capturing images in multiple wavelength ranges using filtered cameras. By dividing the spectrum into distinct bands (e.g., retroreflective band and ambient light band), the system can separately analyze and combine these segments to achieve precise retroreflectivity measurements under varying ambient light conditions
Solution Approach 2:
The patent introduces spectral filtering as an intermediary mechanism. The filtered cameras act as mediators that selectively transmit specific wavelength ranges, allowing the system to isolate the retroreflective signal from ambient light interference while maintaining ease of operation in various lighting conditions
3Measurement precision
If multiple filtered images are captured to estimate ambient intensity, then measurement precision is improved, but device complexity increases due to multiple cameras and filtering
Solution Approach 1:
The patent makes each camera multi-functional by equipping it with switchable or multiple filters. Each camera can operate in different spectral modes (retroreflective measurement mode, ambient light estimation mode), reducing the total number of cameras needed while maintaining measurement precision through flexible spectral selection
Solution Approach 2:
The patent changes the optical parameters (wavelength filtering characteristics) of the cameras dynamically. By adjusting filter selection rather than adding fixed cameras for each function, the system achieves precise multi-spectral measurement with reduced hardware complexity through parameter modulation
4Reliability
If continuous light projection is used instead of strobe, then reliability is improved by avoiding strobe sensitivity, but productivity decreases due to longer measurement time
Solution Approach 1:
The patent performs preliminary spectral characterization during system setup, storing filter transmission characteristics and calibration data. This preliminary action allows the continuous illumination system to quickly process measurements by referencing pre-established spectral models, improving both reliability and measurement speed
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides accurate and reliable retroreflectivity measurements by estimating ambient intensity and compensating for light variations, ensuring consistent results across different lighting conditions without affecting epileptic individuals and reducing measurement time.
Implementation Method 1
a camera apparatus mounted on said structure in spaced apart relationship to said at least one light source and having a field of view including at least a portion of said traffic lane illuminated by said light source during said measurement run, the camera apparatus being selectively sensitive to light at said particular portion of the visible light spectrum
Implementation Method 2
determine a retroreflectivity of said at least a portion of the road marking as a function of said first intensity and said estimated ambient intensity
Data Source
AI summary
A retroreflectivity measurement system comprises a light source arranged to project light across a traffic lane during a measurement run, the light being limited to a particular portion of the visible light spectrum. A camera is selectively sensitive to this light to provide first filtered images and separately selectively sensitive to light at a portion of the spectrum not including the particular portion to provide second filtered images. A controller obtains sequences of first and second filtered images during the measurement run, and identifies within the sequences of images an illuminated road marking; determines a first intensity of the marking from a first filtered image, and a further intensity of the marking from the second filtered images; estimates an ambient intensity of the marking, by applying a scaling factor to the further intensity; and determines a retroreflectivity of the marking as a function of the first and estimated ambient intensities.