We just completed a mobile LiDAR project that was designed to support a roadway resurfacing project in Orlando. The project was centered on the use of mobile LiDAR to generate roadway profile data that Engineers could use to design a resurfacing project. Obviously the data would need to be accurate and we were able to hit the mark and best of all – prove it!
We collected the data using the new Riegl VMX-250 mobile LiDAR unit using a single pass in the north and southbound directions. We only required one pass in each direction to collect the road data which makes it very efficient from the data collection standpoint. In the past, we had to collect “strips” of data and then “sew” them all together during the calibration process. In this case, we took the opposing (NB and SB) strips and calibrated them relative to one another and then they are brought down to control as a final step.
Most of our clients are interested in the overall accuracies of the data, so we have built accuracy assessment tools that make it easy to review the LiDAR against survey control. The tool is simple to use and allows us to sort the results and dig deeper into the least accurate points to see why there might be discrepancies in the control vs the TIN surface.
For this project, we achieved an RMSE of .0525 ft – calculated by comparing the control elevations (Z) against the TIN elevations (Z TIN). This is important because we can check the point cloud against known control that was collected throughout the project and provide detailed information about the accuracy of the data.
Once the data has been calibrated sufficiently, we can then generate all of the derivative products for this project. We generated the following data for our roadway engineers:
- Pavement Cross-Slope
- Shoulder Cross-Slope
- 3D Roadway Markings
- Edge of Friction Course
This data set also supports detailed engineering analysis related to guardrail height above the roadway. This is an important factor to consider because there are specific standards that define where the guardrail is placed, more specifically, its height above the roadway, to corral vehicles that end up impacting the guardrail in an accident situation. The following graphic displays how this measurement can be made in the point cloud data.