The standard workflow for calibrating airborne laser data might not be well suited for laser data gathered using a small unmanned aerial system (UAS) due to the nature of how the data was collected and the inherent dynamic errors of the position and orientation systems typically used with these LIDAR systems. We have adapted the traditional airborne and mobile calibration workflows to meet the need. One uses TerraMatch tie line features, and possibly TerraPhoto Feature Points, for improving the matching of UAS data due to dynamic errors.
- Search for tie lines of type Surface based on ground and (optional) building class using surface lines and slope direction.
- Review the output report and check statistics.
- Check Tie lines for good distribution.
- Run Find Tie Line Match.
- Select Generic system.
- Solve for Heading, Roll, and Pitch (HRP) for the whole dataset, or line groups if there are multiple missions.
- Apply the correction to the tie lines and the laser data if it is significant*.
- If this resulted in a big HRP correction, then Search new Tie Lines, using same settings as before, to obtain best results.
- If incorporating control, search for known Z or known XYZ, as applicable, and add them to your section lines found in the previous step. Ensure both are in the same state of processing.
- Run Find Tie Line Match again to check different parameters on an individual line basis depending on the suitability of the features (tie lines or feature points) in the area. For example:
- Individual Lines: solve for Lever Z.
- Individual Lines: solve for Lever XYZ.
- Individual Lines: solve for Roll shift and Lever Z.
- Individual Lines: solve for Heading, Roll shift, and Lever Z.
- Individual Lines: solve for Roll shift, Lever XYZ.
- TerraPhoto: solve for heading using Feature Points from co-acquired imagery.
- Apply the best correction to the tie lines and the laser data if it is significant*.
- Find Tie Line Fluctuations using different parameters, again depending upon the suitability of the features (tie lines) in the area.
- Solve Z at different rates of change
- Solve XYZ at different rates of change
- Apply the best correction to the tie lines and the laser data if it is significant*
*After each Apply corrections step you should check the flight lines visually in cross sections or using distance coloring to determine if the correction step improved the data. You have to decide if the correction was good or if you need to go back one step and try solving parameters with different settings.
Note: As of TerraPhoto and TerraMatch v019.001 one may use features in images co-acquired with the laser system to find corrections when there are not significant enough suitable features in the laser data alone.