<div dir="ltr"><div>Do you suggest that QGIS is doing the operation at height 0, and not 870?</div><div><br></div><div>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)</div></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Thu, 15 May 2025 at 15:23, Lesparre, Jochem via PROJ <<a href="mailto:proj@lists.osgeo.org">proj@lists.osgeo.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div class="msg-3109086824877501937">
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<p class="MsoNormal">I have coordinates of a triangulation pilar in EPSG:10645 (compound projected CRS: DPnet Saba + Saba height) in an input file:<u></u><u></u></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas">echo 4740.3800 1890.1200 870.3900 > input.txt<u></u><u></u></span></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">The transformation to EPSG:10638 (3D geographic CRS: BES2020 Saba) with PROJ 9.6.0 gives correct results:<u></u><u></u></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas">cs2cs epsg:10645 epsg:10638 --only-best -f %.9f input.txt<u></u><u></u></span></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas">17.635528781 -63.237251291 827.6282</span>[...]<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">I saved the output coordinates to file:<u></u><u></u></p>
<p class="MsoNormal"><span style="font-family:Consolas"> echo 17.635528781 -63.237251291 827.6282 > output.txt<u></u><u></u></span></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">The used transformation is:<u></u><u></u></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas">projinfo -s epsg:10645 -t epsg:10638 -o proj<u></u><u></u></span></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas">Candidate operations found: 4<u></u><u></u></span></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas">-------------------------------------<u></u><u></u></span></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas">Operation No. 1:<u></u><u></u></span></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas"><u></u> <u></u></span></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas">unknown id, Inverse of Saba Transverse Mercator 2020 + Inverse of Saba to Saba height (1) + Saba to BES2020 Saba (1),
<u></u><u></u></span></p>
<p class="MsoNormal" style="text-indent:36pt">[…]<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">However, the location of input.txt and output.txt is visually 0.1 m different in QGIS (version 3.42.2):<u></u><u></u></p>
<p class="MsoNormal">- open input.txt in QGIS (field_1, field_2, field_3 as EPSG:10645)<u></u><u></u></p>
<p class="MsoNormal">- 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):<u></u><u></u></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas">Inverse of Saba to BES2020 Saba (1) + Saba to Saba height (1) + Saba Transverse Mercator 2020<u></u><u></u></span></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">The wrong visualisation of the location of output.txt can be exported in QGIS as CSV geometry AS_XYZ:<u></u><u></u></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas">4740.3647</span>[...]<span style="font-family:Consolas">,1890.2050</span>[...]<span style="font-family:Consolas">,827.6282</span>[...]<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">This is exactly the xy that I get when I transform output.txt back to EPSG:10645 with zero height:<u></u><u></u></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas">echo 17.635528781 -63.237251291 0 | cs2cs epsg:10638 epsg:10645 --only-best -f %.4f
<u></u><u></u></span></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas">4740.3647 1890.2052 42.4286<u></u><u></u></span></p>
<p class="MsoNormal" style="text-indent:36pt"><span style="font-family:Consolas"><u></u> <u></u></span></p>
<p class="MsoNormal">Is this the intended behaviour for QGIS? I don’t like it…<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal">Jochem<u></u><u></u></p>
<p class="MsoNormal"><u></u> <u></u></p>
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