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

[Martin Dobias]

Hi Andreas

On Wed, Dec 13, 2017 at 3:31 PM, Andreas Neumann <a.neumann at carto.net> wrote:
> 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 fact that terrain from below is not rendered is a very common
optimization in 3D rendering called back-face culling - it makes
rendering faster by only rendering triangles that are facing camera.
It is not difficult to turn it off, but I am not sure if the culling
should be turned off by default...

> 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.

Yes this is intentionally locked (for now) as most users would
probably complain if the camera went below the horizon. I understand
you use case though - maybe we can have a underground/caver/geologist
mode for the 3D view that would both disable back-side culling of
terrain and also unlock camera rotation...

Cheers
Martin