[PROJ] QGIS seems to transform with height 0 instead of the actual height

[Javier Jimenez Shaw]

Do you suggest that QGIS is doing the operation at height 0, and not 870?

I have the impression that you are asking at the wrong mailing list ;) (but
I am not in QGIS one, maybe you asked there as well)

On Thu, 15 May 2025 at 15:23, Lesparre, Jochem via PROJ <
proj at lists.osgeo.org> wrote:

> I have coordinates of a triangulation pilar in EPSG:10645 (compound
> projected CRS: DPnet Saba + Saba height) in an input file:
>
> echo 4740.3800 1890.1200 870.3900 > input.txt
>
>
>
> The transformation to EPSG:10638 (3D geographic CRS: BES2020 Saba) with
> PROJ 9.6.0 gives correct results:
>
> cs2cs epsg:10645 epsg:10638 --only-best -f %.9f input.txt
>
> 17.635528781    -63.237251291 827.6282[...]
>
>
>
> I saved the output coordinates to file:
>
>      echo 17.635528781 -63.237251291 827.6282 > output.txt
>
>
>
> The used transformation is:
>
> projinfo -s epsg:10645 -t epsg:10638 -o proj
>
> Candidate operations found: 4
>
> -------------------------------------
>
> Operation No. 1:
>
>
>
> unknown id, Inverse of Saba Transverse Mercator 2020 + Inverse of Saba to
> Saba height (1) + Saba to BES2020 Saba (1),
>
> […]
>
>
>
> However, the location of input.txt and output.txt is visually 0.1 m
> different in QGIS (version 3.42.2):
>
> - open input.txt in QGIS (field_1, field_2, field_3 as EPSG:10645)
>
> - open output.txt in QGIS (field_2, field_1, field_3 as EPSG:10638), where
> I selected this transformation (the inverse of the transformation used by
> cs2cs):
>
> Inverse of Saba to BES2020 Saba (1) + Saba to Saba height (1) + Saba
> Transverse Mercator 2020
>
>
>
> The wrong visualisation of the location of output.txt can be exported in
> QGIS as CSV geometry AS_XYZ:
>
> 4740.3647[...],1890.2050[...],827.6282[...]
>
>
>
> This is exactly the xy that I get when I transform output.txt back to
> EPSG:10645 with zero height:
>
> echo 17.635528781 -63.237251291 0 | cs2cs epsg:10638 epsg:10645
> --only-best -f %.4f
>
> 4740.3647       1890.2052 42.4286
>
>
>
> Is this the intended behaviour for QGIS? I don’t like it…
>
>
>
> Jochem
>
>
>
>
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