[Qgis-user] Z and Elevation

[Greg Troxel]

Sebastian Gutwein via QGIS-User <qgis-user at lists.osgeo.org> writes:

> Manolo,
> You may already know this and be asking a deeper question that I am not
> understanding but in case you are not:
> The Z is the value derived from the geometry itself that QGIS uses to draw
> the location of the point.
> The Elevation is an attribute associated with the point (a field in the
> attribute table).
> There are many reasons that these might not be the same.
> It could be that they were derived from two different sources or there was
> a transformation that occurred that changed the Z value.
> Hope this helps.
> -Bas

I am a beginner with dealing with height/elevation in qgis, but it seems
obvious :-) that the Z value is interpreted with respect to the CRS,
which must necessarily be a lat/lon/vertical.  Some 3D CRSes have
vertical components that are HAE e.g. EPSG:7912, ITRF2014 lat/lon/hae,
and some will have vertical components that are some kind of orthometric
height, e.g. EPSG:5498, NAD83 lat/lon and NAVD88 height.

So "Z should be ellipsoidal" is not in general true.

(Plus, Sebastian's comments sound very useful, and you (Manolo) did not
post your CRS and data schema.)

Greg