Loss of VLR information by TerraScan

With the release of TerraScan v017.001 for CE, TerraScan should now be preserving the projection VLR information in the LAS header. However, when processing with TerraScan, either directly or indirectly through GeoCue, there are some scenarios in which VLRs can be stripped from your data, or at least appear to be removed.

Scenario 1: Reading in LAS data and saving it as Terrasolid’s Fast Binary (FBI) or other non-LAS format.  Since those formats do not support VLRs then TerraScan will remove any such information. If the FBI data is converted back to LAS there is currently no mechanism within TerraScan to restore the VLRs. GeoCue’s LIDAR 1 CuePac has “Update LAS” and “Update Geocoding” steps which may be used to add coordinate reference system information back into an LAS Working Segment.

Scenario 2: Importing points into a TerraScan project will drop the VLRs because TerraScan has no mechanism at this time for conflict resolution if different source files being imported into a project have different VLRs. Hence, TerraScan takes the simple approach of not writing VLRs into the project data files regardless of the storage format selected in the project setup. Creating TerraScan projects using GeoCue does not have this issue as GeoCue handles the conflicts through it’s population process.

Scenario 3: Reading LAS 1.4  PDRF6+ data with a WKT into TerraScan v017.001 for CONNECT edition or later, and then saving the file or running a project macro on the files will result in a the file appearing to drop the VLRs, but the VLRs are still actually present. There is presently a bug in TerraScan that incorrectly sets the WKT bit as false, resulting in subsequent programs reading the file to not show the WKT VLR information.  The forthcoming GeoCue 2017 will be able to fix LAS files that have “lost” their WKT VLR due to the WKT bit being set incorrectly.






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