Texture depth is generated using the line laser. For any position on the road RPS collects 2048 points over a 4.0 meter width (sample density of 2 mm). This data is initially filtered to remove any stray points, and then the general slope of the surface is typically removed to allow compensation in areas of high rutting. This is predominately required for the calculation of Mean Profile Depth (MPD), which relies on the height differences on each side of the profile. Finally the Sensor Measured Texture Depth (SMTD) and Mean Profile Depth (MPD) are calculated. As with other measures this can be displayed as graphs and color maps in the application, exported to tables or exported geospatially.
This technique matches well with sand patch test results, passing the AustRoads standards. It also matches well with point laser results, allowing comparison of texture over time.
Alternatively the texture can be determined via the forward angle of the photometric imaging system. As with the laser system, this system also needs to be calibrated for both image resolution changes and lighting direction changes across the image. It does however allow for a more complete assessment of the surface, due to the high data density, and the detection of the more difficult low texture depth surface such as bleeding on the spray sealed pavement.
Future laser system will incorporate higher resolution cameras, to increase the laser line sample density to less than 1mm, allowing improved performance over the current unit.