[Qgis-user] Z and Elevation

[Manolo Terranova]

Thank you very much.
The relief was made with a GNSS receiver (not from me). The people that
made it are working for a society that handle municipal waste water and
sewers. They use the GNSS as a "tape meter" (with full respect for the
employees that must follow the orders from the boss even if they are not
qualified).

I will try to make the same thing with my GNSS to see what QGIS will say to
me. I would like to understand. I'll let you know.

Thank you again,
Manolo

On Thu, Jun 29, 2023 at 3:35 PM Greg Troxel <gdt at lexort.com> wrote:

> 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!
>
>
>
>
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