KEYWORDS: Roads, Clouds, 3D modeling, Data modeling, 3D scanning, Laser applications, Detection and tracking algorithms, Damage detection, Sensors, Reflection
In order to realize the accurate automatic detection of the potholes depth index of asphalt pavement by laser 3D technology, an iterative datum fitting algorithm is proposed, and on this basis, two judgment methods of the depth index are proposed, and algorithm is developed for automatic recognition. The precision laser point cloud data of road surface was obtained by HandySCAN3D handheld laser 3D scanner, and the validity and accuracy of datum selection and potholes depth calculation algorithm were verified by internal step standard potholes model. The results show that the repeatability of measurement results is less than 5%, and the average error of measurement is less than 3%. The algorithm is further used to detect the actual potholes and compared with the measured results. The error is is less than 3% which verifies the feasibility in practice.
Retroreflective traffic markings are frequently used on roadways to provide guidance to drivers as supplements to regular markings. Portable retroreflectometers are widely used to measure the photometric characteristic of retroreflective traffic markings at present. Portable retroreflectometers include an internal light source and photoreceptors. It is based on the substitution method. Substitution relies on the use of calibrated reference plate. The traffic marking has a low coefficient of retroreflected luminance. It is difficult to measure the coefficient by direct measurement method. The direct measurement method cannot assign measurement values to the reference plates. The paper proposes a new measurement method to solve the problem of measuring the photometric characteristic of the retroreflective traffic marking. It is called the expanded direct luminous intensity method, and it is different from the four methods in JT/T 690 Test Method for Photometric Characteristics of Retroreflectors. The expanded direct luminous intensity method based on CIE angular reference system. A calibrated standard source A illuminates the specimen at a distance of 15 m from the specimen. And a calibrated low-light illuminometer is used to measure the retroreflectivity of the specimen. The paper built a standard system according to this method. The measurement uncertainty of the system is 3.1% while k is 2. After comparing with several different kinds of portable retroreflectometers, the results were satisfactory. Studies have shown that this method and standard system can not only calibrate the reference plates, but also measure the photometric characteristic of retroreflective traffic markings specimens.
Texture depth is defined as the deviations of the road surface profile from the datum plane. It is currently assessed by two methods--sensor measured texture depth (SMTD) and sand patch method (SPM). Many researchers did lots of experiments to study the correlation between these two methods, but ignored the waveform characteristic of the road surface profile. A mathematical model of the road surface profile was built in this paper to calculation of texture depth and compare the two methods. This paper studied the statistical relationship between sensor measured texture depth and sand patch method in different waveform characteristics, and found out that the frequency is the main factor. The results show that the two methods have excellent correlation at the same frequency, and the correlation coefficient R2 is equal to 1. Plates with same frequency were designed to conducted comparison experiments. The result verify the above conclusion. It shows good correlation between the laser detection technology and the volumetric patch technique. Since manufacturers mainly use sand patch method for experiments, the result provides a theoretical basis and technical support for factory inspection. Also, it can be used to get the characteristics of the pavement structure in return.
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