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<p>Javier,<br>
</p>
<div class="moz-cite-prefix">Le 15/09/2022 à 17:56, Javier Jimenez
Shaw a écrit :<br>
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cite="mid:CADRrdKu-+z1bSorn=LGs1v1gCMrxxepehsidkZmvom1-u+gaFw@mail.gmail.com">
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<div>Hi</div>
<div><br>
</div>
<div>I am considering to make a PR that implements
alterCSLinearUnit for BoundCRS (as far as I understand, it is
not covered). My question is: is it enough to apply
alterCSLinearUnit to the baseCRS, leaving the hubCRS and
transformation the same? I would say so, but I do not know if
there is any side effect I am missing.</div>
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<p>Yes, I believe you should only touch the baseCRS of the boundCRS.
At least if the baseCRS is a projected CRS, based on
<a class="moz-txt-link-freetext" href="http://docs.opengeospatial.org/is/18-010r7/18-010r7.html#149">http://docs.opengeospatial.org/is/18-010r7/18-010r7.html#149</a>: "If
the source CRS type is projected and the abridged coordinate
transformation operates in the geodetic CRS domain, the
transformation is deemed to operate on the projected CRS's base
CRS but the projected CRS shall be described."</p>
<p>Said otherwise, the conversion & coordinate system of the
projected CRS are not taken into account for the coordinate
operation described by the boundCRS. Only the (base) geographicCRS
of the projectedCRS is.</p>
<p>Even</p>
PS: <br>
<p>The "interesting" case would be a BoundCRS with baseCRS =
Geographic3D CRS (let's say ETRS89 3D) , targetCRS = Geographic 3D
CRS (let's say WGS84 3D) and transformation = some Helmert. If you
had the crazy idea of altering the vertical unit of the
ellipsoidal height to be feet (hum, is that crazy? who knows what
non-metric folks can do :-)) for the baseCRS, I'm not sure at all
PROJ would do. I guess the expected behaviour when transforming
between such baseCRS with feet vertical unit and the targetCRS
would be first to apply feet -> meter and then chain with the
Helmert transformation. Perhaps this is what we do currently.</p>
<p>actually, checking... yes this works:<br>
</p>
<p>$ projinfo -s "+proj=longlat +ellps=GRS80 +towgs84=1,2,3
+vunits=ft +type=crs" -t EPSG:4979<br>
<br>
PROJ string:<br>
+proj=pipeline<br>
+step +proj=unitconvert +xy_in=deg +z_in=ft +xy_out=rad +z_out=m<br>
+step +proj=cart +ellps=GRS80<br>
+step +proj=helmert +x=1 +y=2 +z=3<br>
+step +inv +proj=cart +ellps=WGS84<br>
+step +proj=unitconvert +xy_in=rad +z_in=m +xy_out=deg +z_out=m<br>
+step +proj=axisswap +order=2,1<br>
</p>
<blockquote type="cite"
cite="mid:CADRrdKu-+z1bSorn=LGs1v1gCMrxxepehsidkZmvom1-u+gaFw@mail.gmail.com">
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<div>The use case I am thinking about: having a bound 2D
(projected) system in something that is not meters (let's say
foot). Then if I do promoteTo3D, the vertical will be meters,
and I want to change the units to the same as the horizontal
ones. It works fine for projected, but not yet for bound.<br>
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<div><br>
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<div>Thanks.<br>
</div>
<div>
<div>
<div dir="ltr" class="gmail_signature"
data-smartmail="gmail_signature">.___ ._ ..._ .. . ._.
.___ .. __ . _. . __.. ... .... ._ .__<br>
Entre dos pensamientos racionales <br>
hay infinitos pensamientos irracionales.<br>
<br>
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