Warning - error importing Georeferenced data (Point Clouds, DEMs, ...) as Point Clouds, STMs or 3SMs in Descartes

Question

If you are dealing with Georeferenced data to build elevation models, then please read this article to prevent errors in Elevations 
 Best Regards

vincent · Answer

Hi Jason, 
 Only Terrain Reality Meshes computed in OpenRoads/Descartes are affected, Reality Meshes computed in ContextCapture are not. But DEMs/pointCouds exported from Contextcapture would (if they are georeferenced and consumed in a georeferenced file.

vincent · Answer

The ellipsoid to geoid reprojection does induce differences with original data: The elevations are distorted, up to 1 m delta on 5cm accurate LiDAR, -12 / +12 m on SRTM 1 arc second SRTM in datasets I checked. 
 Example of delta with 5 cm accurate LiDAR: 
 If the context is to provide environment for renderings, then it might be acceptable, but if the context is to create a surface for computations, this might not be acceptable.

vincent · Answer

Hi Oto, 
 The issue is that elevations are assumed to be relative to ellipsoid (which is usually not the case), and that reprojection may introduce differences relative to original data. 
 As you stated in your answer, if you keep geoid then you will see a large offset. If you project you will have delta as illustrated in my former Email. 
 Reference ID is "Help Ticket 1107277" 
 Best Regards

vincent · Answer

Hi Jason, 
 Happy to read this, I did not used TopoDOT / TerraScan, what I have checked is that the issue happens when both the Point Cloud data and the hosting DGN have a defined GCS, on 2 sample datasets (SRTM and more accurate LiDAR). 
 Results may vary upon datasets/locations. 
 I can't speak for qualification of the issue, workaround is either to work from a non-georeferenced DGN or to strip GCS from Point Cloud/Raster DEM then import. If you are impacted then I would recommend to log a Service Ticket (reference "Help Ticket 1107277")

Warning - error importing Georeferenced data (Point Clouds, DEMs, ...) as Point Clouds, STMs or 3SMs in Descartes

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