Road profiling
In road construction, renovation or expansion, it is a prerequisite for the engineers and scientists to have accurate and reliable data that will have productive work. Currently, most of our roads are faced with the problem of traffic, therefore, the authorities must have a strict measure on the quality of the road they want to be constructed. Use of 3d mapping solutions to do service projects and develop road profiles accurately.
Road profiling is the operation is a measure of “the cross-sectional shape of the road surface in the relation to the road corridor traversing the surrounding landscape” (Acuity, 2011, p. 2). This means that a profile is the longitudinal-section view of the earth along the centerline, and is always viewed perpendicular to the centerline. The profile leveling procedures are used to determine the ground elevations at each of the station points along the centerline, and they are recorded in the surveyor’s book. One of the road profilometry machines used is the PreciCura road profiling sensor.
Lease scanning has more accurate and precise measurements which are vital in road construction. The profilometers are based on the principle of measuring the distance to the road surface from several points along with the measurement vehicle; this is the triangular technique. A laser can be mounted at any angle of up to 50 degrees to the vertical and at a stand of 25 cm high, the measurement width can be increased approximately 61.0cm without increasing the length of the mounting beam. The profiling requires “an accurate, low noise displacement measurement at sample rates in a challenging optical environment; one of the aspects of the road sensor is the ability to handle the sunlight from highly reflective surfaces” (Acuity, 2011, p. 1). Optical filters are used to block most of the reflected light although some will not be blocked. The remaining reflective light will be removed by electronic digital signal processing filters.
It has been noted that “the type of the optical detector used is a sensor and has an essential effect on the performance and the output noise level of the sensor on the presence of the sunlight” (Acuity, 2011. P. 1): These types of two detectors are of two types: the PSD (Position Sensitive Detector) and the line scan camera. A PSD generates a signal to the position of a spot of light on its surface; if that spot of light falls on a detector, the PSD signal is affected.
Measurement principles
The lasers scan e.g. the PreciCura measures the distance using the laser-based optical triangulation:
A laser spot is projected on the surface of the material to be measured. the laser spot is projected on the surface (water levels, window glass thickness and distance to perfect mirrors cannot be measured). When the material is inside the measurement range of the laser scanner a portion of light is picked up by lens system that focuses the image of the spot on the CCD (Charged Couple Device) detector. The CCD is an image device with light sensitive cells (pixels) and the image will cover several pixels. Then the processor in the laser scanner will convert the pixels to distance value from an individual calibration table stored in the sensor.post processing of the distance value includes filtering, and reduction of measurement frequency i.e. measurement of speed. (Acuity, 2011, p. 2)
The road profiling system incorporates the non-contact lasers sensors to measure the surface and accelerometer of the road to compensate for the effects of the vehicle’s movements. Roughness testing is carried out along a road system using a motor vehicle. The operating signal at the beginning of each segment as the vehicle travels, the laser sensors make measurements:
At the rate of 32000 per second, and the profile value is recorded at an interval of every six inches per mile. The results obtained are of pavement roughness testing are international roughness index (IRI) values, expressed in terms of slope i.e. inches per mile.IRI is the internationally accepted scale for roughness, it is a computer-based system (virtual-based system) determined by obtaining suitable measurement of the profile of the road processing it through an algorithm that simulates the way a reference vehicle would respond to the roughness inputs and accumulating the suspension travel. The scanned data is filtered and modeling of the road is done by design software. (Limab, 2011, p.1)
However, some parameters influence the accuracy of laser scanning in road profiling. The first error arises due to the instruments that are used, instrumental error, brought by error due to distance measurement system and angle measurement system. Secondly, the error is brought by natural constraints, (this is through surface properties i.e. surface color and surface brightness) and the angle of incidence. Finally, there could be an error due to the dark color and small angle of incidence leading to lower intensity of reflected laser beam which causes the increase in measurement noise resulting in decreasing accuracy (Jaakkola, 2006, p.1).
Conclusion
Road profiling using laser scanning is the best method as it is accurate with the right accurate measurements which are a prerequisite for road analysis.
References
Acuity. (2011) Laser Displacement Sensor for Road Profilometry. Web.
Jaakkola, M. (2006) Kinematic Vehicle Laser Scanning Of Roads. Web.
Limab. (2011) High precision laser sensors for dimensional measurement. Web.