[QGIS-Developer] QGIS 3D: looking below the terrain model

[Andreas Neumann]

Hi,

Being a caver, I have a lot of underground data. Thanks to the support 
from Martin I got them to load correctly as 3D polygondata.

However, one issue I have is that the terrain rendering disappears when 
I look below the terrain model surface - which isn't so nice for a caver 
or geologist. Is this also an issue about culling? Would it be possible 
to enable the rendering of the backside of the terrain surface?

The other issue I have is that tilting is somehow locked at the horizon. 
I can look down on the terrain and then rotate the whole model until I 
look sideway into the model, but than the rotation is blocked. I cannot 
rotate any further so that my camera gets below the surface and that I 
could move below the surface and look up towards the terrain. I guess 
this makes a lot of sense for people who do not need to explore things 
below the terrain surface, but for geologists or cavers, it would be 
great if this rotation/tilting blocking could be disabled somehow.

Thanks,

Andreas