[QGIS-Developer] Scale z value to match 3d view dem scaling?

[Martin Dobias]

Hi Nyall

On Mon, Jul 30, 2018 at 5:19 AM, Nyall Dawson <nyall.dawson at gmail.com> wrote:
>
> I was chatting with Mathieu trying to work out if there was a bug in
> 3d map views, but it turns out that it was just a misunderstanding on
> my part. I thought that if I had e.g. a pointz dataset (with z value
> set to dem spot height) and a dem, the points should always be placed
> exactly on the dem when altitude clamping = absolute.
>
> It turns out that this is only the case if the dem vertical scale is
> set to 1.0. If I increase the scale, then the point z values aren't
> scaled to match and end up sitting below the dem.
>
> To me this is a bug, because vertical scale is a view dependent "data
> visualisation" setting only, and shouldn't require modification of the
> original data itself (i.e. manually scaling the point z values to
> match the vertical scale*).
>
> Is this intended behavior? (and if so, can it be rethought?)

It is possible that there are some inconsistencies with the vertical
scale terrain and how it applies (or does not apply to other
entities). One thing that comes up every now and then is whether all
vertical distance values should be affected by the vertical scale - or
just some - or maybe to have that configurable. For example, as you
say, for PointZ data, it probably makes more sense to apply vertical
scale to Z coordinates. How about other properties like polygon
elevation or extrusion - should those be affected as well? Any
thoughts on how this should work are welcome :-)

Cheers
Martin