Rapid Road Sections
The methodology consists of travelling the visible centre line with a survey vehicle equipped with a precision GPS recording horizontal and vertical position data at approximately 5 meter intervals. In the same vehicle and mounted directly below the GPS antennae there are two pulsed laser rangefinder instruments. These gather vertical angles and slope distances to the left and right road detail. All data are recorded on a central computer in the vehicle and the xyz position data of the edges are calculated simply and directly at the same time.
As a variation on the above setup, a single man solution is also viable with the inclusion of an IMU for pointing direction.
In case of rehabilitation work, five long sections (left earthworks limit, left edge, centre line, right edge and right earthworks limit) are typically surveyed. In the case of new alignments on reasonably flat ground, only two or three are picked up. Spacing of the DTM points will depend on the final cross section spacing that is to be adopted and will have little bearing on the volume of work. Any areas along the route that have a requirement for extra detail (such as culverts and intersections) the vehicle stops and extra survey work is done.
Previous work with this system has resulted in accuracy’s (RMS) of 5cm or less on all three axes. Being based on the prior control survey and precision GPS fixes, any errors will be random in nature rather than cumulative.With a double laser system, progress of this survey in the field is usually more than 20 kilometers a day.