A few things to keep in mind when using TerraScan’s Compare with Reference tool for change detection:
- Compare with Reference tool only works on loaded points
- The first step in debugging your settings is to make sure that TerraScan is loading points from the reference project when you open a block in the active project as the tool only works if reference points are loaded together with the points of the active block. A quick look at the number of points loaded with and without the reference option should tell you if your project is configured correctly.
- When you open the block, make sure that “Load reference points” is switched on. The option is only available if a reference project is set in the project settings.
- It is required that different classes are set for ground and object comparison, even if no classification is applied for one or the other comparison. However, the same class numbers can be used in active and reference projects.
- If you don’t want to compare object classes you should set ‘Active to class’ and ‘Ref to class’ to ‘Do not classify’, but still, the object class numbers must be different from ground class numbers.
- The tool is supposed to find overlapping tiles spatially so the reference project does not need to have the same block names or definition as the active project
- Ground comparison produces the opposite of what is stated in the manual and opposite of what one would intuitively think based upon the dialog
- Object comparison appears to have no consideration for the fact that there is also a vertical component provided by the dz tolerance resulting in all the points within the specified radius of the reference point to not get classified