[Qgis-user] 3D Map View: Issue with Terrain altitude clamping

[Guilhem Vellut]

>
> Hello,

I am on QGIS 3.8 and I try to setup a 3D visualization. I am on MacBook Pro
13'' 2018 with an Intel Iris Plus Graphics 655 graphic card.

As data, I have a SHP layer with building footprints (polygons) and a
building height attribute (no absolute altitude though), as well as a DEM
raster (SRTM).


I am trying to setup a 3D Map View: In the "3D View" layer properties for
the building layer, I use the height attribute as extrusion and leave the
height at 0. Then for the altitude clamping, I choose Terrain.

My expectation is that the altitude of the buildings will be taken from the
terrain layer configured in the 3D map view and then the extrusion will
happen on top of that.

However, what I get instead in the 3D map view is all my buildings floating
at the same altitude and well above the terrain (see the screenshot at
https://ibb.co/mzPVC1w ). The extrusion seems to work fine. I have tried
with a smaller DEM (cut to the extent of the building layer) but this time
the buildings get below the DEM (see https://ibb.co/FKrJynd ).

Is my expectation about the Terrain altitude clamping wrong ? And it is
supposed to do something completely different ? If it is right, has anyone
managed to make it work (maybe using a different graphic card) ?

Also what is the difference between Terrain altitude clamping and Relative
altitude clamping ?

Thank you for your help.

Guilhem
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