[Qgis-user] Z and Elevation

[Greg Troxel]

Manolo Terranova <manoloterranova at gmail.com> writes:

> EPSG 32632

The zip had a shapefile tagged as 32632, with (per ogrinfo):

  Name: String (16.0)
  Code: String (60.0)
  Northing: Real (18.5)
  Easting: Real (18.5)
  Elevation: Real (18.5)
  OGRFeature(Ponti):0
    Name (String) = cs004
    Code (String) = pn
    Northing (Real) = 5030233.30810
    Easting (Real) = 631584.78631
    Elevation (Real) = 103.18448
    POINT ZM (631584.786313961 5030233.30810281 147.350793083198 1371918614)

  OGRFeature(Ponti):1
    Name (String) = cs005
    Code (String) = pn
    Northing (Real) = 5030233.28520
    Easting (Real) = 631584.74959
    Elevation (Real) = 103.17660
    POINT ZM (631584.749590836 5030233.28520391 147.342911031097 1371918631)

  OGRFeature(Ponti):2
    Name (String) = cs006
    Code (String) = pn
    Northing (Real) = 5030235.54719
    Easting (Real) = 631549.52750
    Elevation (Real) = 103.27301
    POINT ZM (631549.527499332 5030235.54718945 147.438223647885 1371918715)

The first two points are perhaps the same place, and the third is ~35m
away.  The M value is unlabeled, but obviously timeval, 22 June 2013 1630 UTC
ish.

That is a 2D CRS: WGS 84 / UTM zone 33N.  It has no altitude.  So having
a Z value does not make sense, but that may be because "POINT M" is not a
thing, at least in Postgis:
  https://postgis.net/docs/ST_MakePoint.html

So:

  How did you obtain this data?

  Was it autonomous GPS?  SBAS differential?  RTK?  PPP?

  What is the basis of your belief that the data is in 32632?

  [ Standard rant: It is just about inconceivable that you could have
  made measurements in the WGS84 ensemble, but perhaps you did RTK and
  that reference station only has ensemble coordinates :-) ]

  Where did the Z values come from?

  Why did you store the data in a 2D CRS if it is 3D data?  Or if it is
  not 3D data, why isn't the Z field consistently 0 or some other undef
  codepoint?

  Where did the easting/northing/elevation values come from?  The
  easting/northing look copied from the POINT values.

  What do you think the altitude of the points ought to be, in the datum
  used as HAE, as WGS84 Orthometric Height, or some other orthometric
  height datum?

Overall, the basic issue is your data, not anything about qgis.  You
need to understand that measurement pathway and be able to answer the
"why/how" and "I'm skeptical; show me the evidence" questions.  If
someone gave you the data file without explaining that, ask them the
above questions.  Feel free to tell them the Internet said to be
difficult!