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

[Nyall Dawson]

On 14 December 2017 at 20:41, Martin Dobias <wonder.sk at gmail.com> wrote:
> 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...

Could we give the terrain some small "thickness", and add a duplicate,
slightly lower surface facing downwards below the existing DEM?

Nyall