Datum Transform Warning

When attempting to convert point coordinates from one horizontal projection to another using LP360 or True View EVO, the user may see a warning message with the heading: “Datum Transform Warning!” if the datums of the projections differ or appear to differ based on their WKT. Before attempting to perform any coordinate system transformation/reprojection, it is very important that the user knows the initial/input coordinate reference system (CRS) definition for the LAS data that needs to be transformed. 

NAD83(2011) to NAD27 Transformation

It is possible to perform a datum transformation between NAD83 and NAD27 using LP360 standalone. To perform this function, simply use the Reproject/Shift LAS PCT. Keep in mind that U.S. Survey feet is the only unit natively supported for NAD27 horizontal datum in LP360. Users may add their own horizontal coordinate system to LP360 using a properly formatted PRJ.

Since the source and destination Spatial Reference System have different datums, the user will see the following warning. However, this datum transformation is incorporated and the user can click “Yes” to proceed: 

NAD83(2011) to NAD27 Datum Conversion – Warning Message

Note: This has only been tested on a subset of data. To verify the accuracy of the any transform/reprojection, it is always a good idea to compare the output dataset to control points to verify that the function has worked properly.

WGS84 to NAD83 Transformation

When converting between WGS84 and NAD83 datums, when using the Reproject/Shift LAS PCT in LP360, the user will observe the following warning message:

WGS84 to NAD83(2011) Conversion

It is important to note that where the NAD83 datum is one of the realizations more current then the original one, that the transformation between these datums, such as NAD83(2011) and WGS84, has not yet been implemented in the Reproject/Shift LAS PCT. However, if you need to perform the datum transformation, the user will need to use the deprecated Reproject LAS Files tools available with LP360 for ArcGIS. The LP360 toolbox tools need to be added to the ArcToolbox to use the Reproject LAS Files tool. When using this tool, ensure the incoming and outgoing spatial references are defined properly before starting the process. The user may not specify the datum transformation to be used. The tool will use the ArcMap default datum transformations.

Repoject LAS Files Settings

Note: Keep in mind that the list for vertical datums is not as complete in ArcGIS, if you wish to shift the vertical at the same time as the horizontal datum. Best practice is to perform the horizontal transformation in ArcGIS, then transform the vertical datum using the Reproject/Shift LAS PCT in LP360 Standalone.

Share

GeoCue Group Support

GeoCue Group Support has written 727 articles

Leave a Reply