<div dir="ltr">If your input data does not need time stamps, you may be able to work around this using +omit_fwd/+omit_inv selectors and a set of axisswap order=1,2,4,3 steps? </div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">Den tors. 14. dec. 2023 kl. 14.13 skrev Lesparre, Jochem via PROJ <<a href="mailto:proj@lists.osgeo.org">proj@lists.osgeo.org</a>>:<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-3696964243730219408">
<div lang="NL" style="overflow-wrap: break-word;">
<div class="m_-3696964243730219408WordSection1">
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt">Hi list members,<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt">The PROJ operations
</span><span lang="EN-GB" style="font-size:10pt;font-family:Consolas">+proj=push</span><span lang="EN-GB" style="font-size:10pt"> and
</span><span lang="EN-GB" style="font-size:10pt;font-family:Consolas">+proj=pop</span><span lang="EN-GB" style="font-size:10pt"> use "last in, first out" (LIFO) to store and retrieve coordinate values in a stack. It seems that I need "first in, first out"
(FIFO) or other new functionality in PROJ.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt"><u></u> <u></u></span></p>
<p class="MsoNormal"><i><u><span lang="EN-GB" style="font-size:10pt">Problem<u></u><u></u></span></u></i></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt">The Dutch Caribbean islands use TM-projections based on old datums. We have an exact Helmert transformation per island that transforms the horizontal coordinates to an ITRS realisation at a specific
epoch. For some islands we need a geoid (EGM2008 sampled at 45” is the best we have at the moment) for the height transformation from local levelling heights to ITRS. That works fine for a forward transformation with this PROJ pipeline:
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">cct +proj=pipeline
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=push +v_3
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=tmerc +inv +lat_0=12.180658675 +lon_0=-68.251802281 +k_0=1 +x_0=23209.5600 +y_0=21423.9900 +ellps=intl
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=cart +ellps=intl
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=helmert +x=-366.1939 +y=-115.0688 +z=-776.7039 +rx=20.963080 +ry=16.462749 +rz=-14.276379 +s=-12.80900 +convention=coordinate_frame +exact
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=cart +inv +ellps=GRS80
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=pop +v_3
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=vgridshift +grids=egm2008_0_45.tif +inv
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt">However, I do not get exactly the same results for the inverse transformation with
</span><span lang="EN-GB" style="font-size:10pt;font-family:Consolas">-I</span><span lang="EN-GB" style="font-size:10pt">, since I apply the geoid on the ITRS coordinates, but then the physical height is used for the Helmert transformation instead of the
correct ellipsoidal height. This gives a small error in the horizontal coordinates in this case, but can easily reach more than 50 metres for other CRSs.<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt"><u></u> <u></u></span></p>
<p class="MsoNormal"><i><u><span lang="EN-GB" style="font-size:10pt">Solution<u></u><u></u></span></u></i></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt">The most elegant solution seems to me to use FIFO for operations +proj=push and +proj=pop, so I can use this pipeline:<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">cct +proj=pipeline
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=push +v_3
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=tmerc +inv +lat_0=12.180658675 +lon_0=-68.251802281 +k_0=1 +x_0=23209.5600 +y_0=21423.9900 +ellps=intl
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=cart +ellps=intl
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=helmert +x=-366.1939 +y=-115.0688 +z=-776.7039 +rx=20.963080 +ry=16.462749 +rz=-14.276379 +s=-12.80900 +convention=coordinate_frame +exact
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=cart +inv +ellps=GRS80
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=push +v_3<u></u><u></u></span></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=pop +v_3
<u></u><u></u></span></b></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=vgridshift +grids=egm2008_0_45.tif +inv
<u></u><u></u></span></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=pop +v_3 +omit_fwd
<u></u><u></u></span></b></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt"><u></u> <u></u></span></p>
<p class="MsoNormal"><i><u><span lang="EN-GB" style="font-size:10pt">Alternative<u></u><u></u></span></u></i></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt">Another possible solution is a new PROJ operation e.g.
</span><span lang="EN-GB" style="font-size:10pt;font-family:Consolas">+proj=flip</span><span lang="EN-GB" style="font-size:10pt"> to make the values of a coordinate value and the value stored in the stack switch places.
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">cct -I +proj=pipeline
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=push +v_3
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=utm +zone=19 +inv +ellps=intl
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=cart +ellps=intl
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=helmert +x=-366.1939 +y=-115.0688 +z=-776.7039 +rx=20.963080 +ry=16.462749 +rz=-14.276379 +s=-12.80900 +convention=coordinate_frame +exact
<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=cart +inv +ellps=GRS80
<u></u><u></u></span></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=flip +v_3
<u></u><u></u></span></b></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=vgridshift +grids=egm96_15.tif +inv
<u></u><u></u></span></p>
<p class="MsoNormal"><b><span lang="EN-GB" style="font-size:9pt;font-family:Consolas">+step +proj=pop +v_3 +omit_fwd
<u></u><u></u></span></b></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:9pt;font-family:Consolas"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt">Regards, Jochem<u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB" style="font-size:10pt"><u></u> <u></u></span></p>
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