<div dir="ltr">Thanks!<br></div><br><div class="gmail_quote gmail_quote_container"><div dir="ltr" class="gmail_attr">On Mon, 3 Feb 2025 at 16:54, Even Rouault <<a href="mailto:even.rouault@spatialys.com">even.rouault@spatialys.com</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"><u></u>
<div>
<p>Javier,</p>
<p>you can probably hack around BOUNDCRS in a totally PROJ-specific
way by using the "METHOD["PROJ-based operation method:
{proj_pipeline_here}" <br>
</p>
<p>For example with the following file, 'projinfo -s @/tmp/tmp.wkt
-t "WGS 84"' will return the specified pipeline<br>
</p>
<p>BOUNDCRS[<br>
SOURCECRS[<br>
GEOGCRS["unknown",<br>
DATUM["Unknown based on GRS 1980 ellipsoid",<br>
ELLIPSOID["GRS 1980",6378137,298.257222101,<br>
LENGTHUNIT["metre",1]]],<br>
PRIMEM["Greenwich",0,<br>
ANGLEUNIT["degree",0.0174532925199433],<br>
ID["EPSG",8901]],<br>
CS[ellipsoidal,2],<br>
AXIS["longitude",east,<br>
ORDER[1],<br>
ANGLEUNIT["degree",0.0174532925199433,<br>
ID["EPSG",9122]]],<br>
AXIS["latitude",north,<br>
ORDER[2],<br>
ANGLEUNIT["degree",0.0174532925199433,<br>
ID["EPSG",9122]]]]],<br>
TARGETCRS[<br>
GEOGCRS["WGS 84",<br>
DATUM["World Geodetic System 1984",<br>
ELLIPSOID["WGS 84",6378137,298.257223563,<br>
LENGTHUNIT["metre",1]]],<br>
PRIMEM["Greenwich",0,<br>
ANGLEUNIT["degree",0.0174532925199433]],<br>
CS[ellipsoidal,2],<br>
AXIS["latitude",north,<br>
ORDER[1],<br>
ANGLEUNIT["degree",0.0174532925199433]],<br>
AXIS["longitude",east,<br>
ORDER[2],<br>
ANGLEUNIT["degree",0.0174532925199433]],<br>
ID["EPSG",4326]]],<br>
ABRIDGEDTRANSFORMATION["Transformation from unknown to WGS84",<br>
METHOD["PROJ-based operation method: +proj=pipeline +step
+proj=axisswap +order=2,1 +step +proj=cart +ellps=GRS80 +step
+proj=helmert +x=1 +step +inv +proj=cart +ellps=WGS84"]]]<br>
<br>
</p>
<p>Otherwise having records in the DB will certainly be cleaner.
data/sql/transformations_czechia_extra.sql can probably be used as
an example of quite advanced transformations, including using a
grid referenced in a projected CRS.</p>
<p>Even<br>
</p>
<p><br>
</p>
<div>Le 03/02/2025 à 16:26, Javier Jimenez
Shaw via PROJ a écrit :<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>Hi</div>
<div><br>
</div>
<div>I am trying to make this transformation (that is not in
EPGS). I do not know how far I can go with PROJ.</div>
<div><br>
</div>
<div>(Apparently this transformation is needed to go from the
coordinates used by HEPOS.gr, the Greek positioning system, to
the official -I think- CRS in Greece, <span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none">GGRS87</span>.</div>
<div>The best is that the transformation would be in EPSG. Do
you know anybody in Greece with the proper contacts? I am
happy to talk with them about it, and help if needed)</div>
<div><br>
</div>
<div>Until it is in EPSG, I would like to use PROJ to do it.<br>
</div>
<div><br>
</div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none">The
accurate transformation from ETRS89 to GGRS87 is something
like:</span></div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none">-
apply a Helmert transformation</span></div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none">-
Project into a transverse Mercator</span></div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none">-
Apply a correction grid. Yes, in the projected system.<br>
</span></div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none">-
(optional) go back from the projected to the geographic crs.</span></div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none"><br>
</span></div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none">I
thought about several options:<br>
</span></div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none"><br>
</span></div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none">-
First option: create a WKT2 with a BOUNDCRS that defines the
transformation. Can it be done in a single WKT2?<br>
</span></div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none">-
Second option: add the transformation to proj.db. Is it
doable?<br>
</span></div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none">-
Third option: Create "my own grid" file (in the geographic
system) combining all the steps. Of course, it will loose
some accuracy due to the new grid interpolation.<br>
</span></div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none"><br>
</span></div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none">Any
clue?</span></div>
<div><span style="color:rgb(34,34,34);font-family:Arial,Helvetica,sans-serif;font-size:small;font-style:normal;font-variant-ligatures:normal;font-variant-caps:normal;font-weight:400;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;word-spacing:0px;white-space:normal;background-color:rgb(255,255,255);text-decoration-style:initial;text-decoration-color:initial;display:inline;float:none">Thanks.<br>
</span></div>
</div>
<br>
<fieldset></fieldset>
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</blockquote>
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</blockquote></div>