A mobile (truck-mounted) imaging system uses laser-based technology to obtain accurate quantitative data in real time and at high speeds regarding the conditions of road and highway surfaces. Specifically, the GIE Technologies laser vision system integrates a three-dimensional laser-sensing imaging sensor array to map the cracks, ruts and roughness of road surfaces. The LaserVision System simultaneously records a three-dimensional information along with photometric data using the same set of Biris (bi-iris) sensors. These sensors were developed for this application by engineers at GIE Technologies Inc. under exclusive license from the National Research Council (Ottawa, Canada). They rely on a combination of defocusing and triangulation principles to record 3D information about a test surface. The Biris approach, for a mobile pavement testing system, offers several performance advantages in comparison to other sensing methods. Most important, a Biris sensor uses all- solid-state components with no moving parts. This rugged design is highly resistant to misalignment and performs well in a moving, continuously vibrating vehicle. The photometric (intensity) information provides complementary data where ranging alone proves insufficient, as when detecting pavement markings, sealed road cracks or patches. In addition, the range analysis uses simple trigonometry to obtain real-time performance.
Previous developments of Biris technology for road inspection application sled to the birth of a very rugged high power 3D sensor using a three-line laser projector. In this hostile environment where shock, vibration, dust and dirt are constantly present, 3D ranging must comply with very severe demands. Resolution, precision and reliability are strictly observed. The new approach keeps the same data density but uses high frame rate image capture and feature extraction. With high speed capture, the number of actual laser projections can be reduced to one, without having to decrease the number of measured profiles per second. This eases the data processing by keeping the same characteristics for the projected line from one acquired profile to the next and over the whole acquisition sequence. The data rate achieved maintains the maximum 10 cm profile spacing for the road surface sampling up to speeds of 72km/h. Range measurements and intensity I, are obtained for each measured point. The field-of-view and depth of field for this sensor are very important characteristics which are adapted for the application. However this solution implies a new sensor design and an optimized image capture geometry. Triangulation and defocusing are used to improve the signal to noise ratio and to provide immunity to false measurements.
This paper describes the analysis and identification of road surfaces 3D distress characteristics by means of a three- line laser sensor. A laser-based vehicle-mounted imaging system simultaneously evaluates several conditions of road surface distress, such as ruts, cracks, and surface roughness. The 3D feature extraction is done by a combination of two measuring techniques: triangulation and defocusing. A generated pattern of transverse profiles spaced by 11 cm, is used to sample the road surface. Physical differences between profiles (beam shaping, back- scattering angles, etc.) require special signal processing and analysis techniques in order to reconstruct a 3D image. A new fuzzy system is applied to the analysis and identification of surface cracks. The fuzzy reasoning takes into account the vagueness and the subjectivity of the classification process provided by human experts in the formulation of the identification criteria. This approach is based on a limited number of linguistic fuzzy rules given in natural language, which are extracted from the experimental description of road surface characteristics. Based on a limited number of dispersed events, the fuzzy system is able to predict the evolution of the cracking on the road surface. Theoretical aspects and experimental results are presented.
KEYWORDS: Sensors, Roads, Semiconductor lasers, Calibration, High power lasers, CCD cameras, CCD image sensors, Prisms, Camera shutters, Data acquisition
This paper describes a sensor that employs three laser beams in order to measure the 3-D distress characteristics of road surfaces at highway speed. The 3-D feature extraction is done by means of a combination of two measuring techniques: triangulation and defocusing. In order to generate a pattern of transverse profiles spaced by 11 cm at a speed of about 20 m/s, three transverse profiles are acquired in a single frame, at a frame rate of 60 Hz. This approach led to the three laser beam solution and the use of a standard CCD camera as detector. Subject analysis emphasized as a 'must have': a wide field of view, low blurring, a more even distribution of the laser line intensity, a low power consumption along with simplicity and low cost. The use of a modified reversed prism provided a more uniform distribution, even with a single laser for each projected line. High power laser diodes were needed in order to operate at 1/10,000s shutter speed. An accurate sensor calibration provides 256 points of z (range), x (position) and I (intensity) for each profile. Calibration data as well as range and intensity of measured profiles are provided. Sensor's accuracy is also observed.
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