Objects that are detectable in both point clouds, such as poles, can be used to match an MLS point cloud to a reference point cloud. TerraMatch can find tie lines for objects, if points from the single objects are grouped and if groups of one object type are classified into a separate class (e.g. each pole is one point group and all poles are in point classes "MLS Poles" and "ALS Poles", respectively). The shape of the object is not considered when the software finds the groups in the different lines. Therefore, the search works also for other types of objects than poles.
1. Make sure that the line numbers in the ALS and the MLS point clouds are distinguishable.
2. Assign groups and classify points on objects that you want to use for matching. This must be done for both, the MLS and ALS point clouds. See TerraScan User Guide for more information about grouping and classification.
3. Start Define tie lines. In the Tie line settings dialog, set the class numbers of objects in the ALS and MLS point cloud as Object classes.
4. Start Search tie lines and search for Group objects. The software places Xyz tie points for objects.
5. Check tie lines. Check worst tie point positions and delete, if bad.
6. Select Fix lines command and define the line number range of the ALS point cloud. This defines the ALS lines as reference for matching the MLS lines and the type of the tie points is changed to Known xyz.
7. Select Find tie line fluctuations tool to match the MLS lines to the ALS point cloud.