Using orthophotos and ground points
Orthophotos or intensity images and ALS ground points can be used as reference for matching MLS data. The orthophotos or intensity images may provide features for collecting tie points for XY correction while the ground points can be used for collecting tie points for Z correction.
1. Attach orthophotos or intensity images as raster reference in TerraPhoto.
2. Collect Known xy tie points or lines manually from any objects that can be sees in the attached raster images and the MLS point cloud (corners of paint markings, manhole covers, paint lines, etc.). The known XY location is derived from the raster images and TerraMatch computes the horizontal difference between the MLS data and the known location.
3. Use Report gaps tool to see if there are longer Xy gaps. Add tie lines in places of long gaps if possible.
4. Solve fluctuating Xy correction.
5. Apply correction to MLS data.
You may write a new copy of the data set.
6. Check for remaining internal XY mismatch. If there is any, apply another internal XY correction derived from Wall tie lines or another tie line type applicable to the data set.
7. For collecting Z tie points/lines, you can use, for example, the trajectories of the MLS data set. Draw the xy-corrected trajectories into the CAD file. Drape the lines to the ALS ground points. The trajectory lines now represent the ground level of the ALS data set.
8. Select trajectory lines draped to the ALS ground points.
9. Select Import points / From selected vectors and collect Known Z points. Each vertex of the selected lines becomes a tie point.
10. Delete tie line observations with longer than about 8.0 m range. For elevation adjustment, use only observations close to scanner.
11. Check worst tie point positions and delete, if bad. Filter bad tie lines, if necessary.
12. Solve fluctuating Z correction using a smooth curve.
13. Apply correction to MLS data.
You may write a new copy of the data set.
