I have a project with GCPs imported using a given CRS (an old EPSG:27562 Lambert Centre France CRS), and therefore also set my project CRS to this same EPSG:27562 CRS.The Z coordinate of these GCPs is expressed not as height above ellipsoid, but using the altitude expressed in the NGF-IGN69 datum, official for France.
When I export the pointcloud using this same CRS, then the Z coordinate of the points is correctly expressed in the NGF-IGN69 french datum.
However, when I export the dense cloud to the more recent EPSG:3947 CRS (Lambert-93 RGF93 CC47), then the Z coordinate is modified - although it should also be expressed in the NGF-IGN69 vertical datum and not the height above ellipsoid. The whole pointcloud is then offset roughly 44.60m along +Z. The strange thing is that this offset is not exactly the difference between the height above ellipsoid and NGF-IGN69 which has a mean of 46.177 across all my topo points.
Do you know if this is a known bug? Is there a workaround to prevent RC from modifying the Z coordinate durnig the export with an output CRS different from the project CRS but which share the same vertical datum?
Thanks in advance!