Cloud to cloud matching
This method tries to match one point cloud to a reference point cloud by using only planar surfaces that are detectable in both point clouds. This requires a good amount of points that represent the planar surfaces. Best candidates for matching an MLS point cloud to an ALS point cloud are the ground, mainly for vertical matching, and building walls for horizontal matching. Horizontal matching is only possible if there are enough points from vertical walls also in the ALS point cloud.
1. Set the TerraScan project for the ALS point cloud as the reference project for the MLS project. See Reference project exists option in the Project information dialog of TerraScan. If loaded points are used, the reference points can be loaded into TerraScan with the Read reference points command. If a project block is loaded, the Load reference points option must be switched on.
2. Compute normal vector and dimension attributes for the MLS data set by using either the macro step or the menu command for loaded points in TerraScan.
3. Start Define tie lines. In the Tie line settings dialog, set the class numbers of potential point classes (such as ground, walls, etc.) in the ALS and MLS point cloud as Cloud classes.
4. Start the cloud-to-cloud tie line search in TerraMatch.
5. Check worst tie point positions and delete, if bad. Filter bad tie lines, if necessary.
6. Solve fluctuating corrections using a smooth curve.
7. Apply correction to MLS data.
You may write a new copy of the data set.
This matching method can be extended by introducing Known Xy tie points for a better horizontal match, especially if there are not enough building walls that can be used. The additional tie points for horizontal matching may be produced as described in the Using orthophotos and ground points section.
