<div dir="ltr">Javier,<div><br></div><div>I'm not sure we are concerned with the same use case, but your mention of explicitly stating grids made me think there could be overlap with our goals. </div><div><br></div><div>We are interested in explicitly stating the vertical datum as a combination of grids in WKT(2), but we have been unsuccessful in making this work operationally. We started working at a VERTCRS with a DERIVINGCONVERSTION as described <a href="https://github.com/noaa-ocs-hydrography/vyperdatum/blob/8d2a83d78f74a926dc746da6604fb4a051086530/vyperdatum/vypercrs.py#L458" target="_blank">here</a>, but this didn't seem to get where we wanted to go. At this point we are creating a compound CRS with a very simple VERTCRS with a remarks section that contains the PROJ pipeline string (example <a href="https://github.com/noaa-ocs-hydrography/vyperdatum/blob/8d2a83d78f74a926dc746da6604fb4a051086530/vyperdatum/vypercrs.py#L530" target="_blank">here</a>). This solution is somewhat hamstrung by the remarks section being stripped out of the WKT with GeoTIFFs, so at this point we have created a custom GDAL Tiff Tag VERTICALDATUMWKT to store this information (example temp link <a href="https://noaa-ocs-nationalbathymetry-pds.s3.amazonaws.com/index.html#Bluetopo/US5NH1AH/" target="_blank">here</a>) until we can find a better solution. [A side note for anyone that wants to know why we did not just use the epsg code for NAVD88 in the above example: <a href="https://epsg.org/crs_5703/NAVD88-height.html">NAVD88 as EPSG</a> is declared as an ensemble of many different geoids which we prefer not to have included.]</div><div><br></div><div>While our process is tied into a bunch of business logic, we are interested in making the data we make public as accessible as we can. If there are thoughts about how to solve this problem in a better way that facilitates downstream use through explicit declaration of the grids in WKT I think we would be interested in hearing other approaches.</div><div><br></div><div>Regards,</div><div>Glen</div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Nov 29, 2021 at 11:12 AM Javier Jimenez Shaw <<a href="mailto:j1@jimenezshaw.com" target="_blank">j1@jimenezshaw.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"><div dir="ltr">I was thinking on a WKT that defines the offset as part of the CRS defintion, in a similar way the geoid grid file can be defined.<br clear="all"><div><div><div><div dir="ltr">.___ ._ ..._ .. . ._. .___ .. __ . _. . __.. ... .... ._ .__<br>Entre dos pensamientos racionales <br>hay infinitos pensamientos irracionales.<br><br></div></div><br></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, 29 Nov 2021 at 17:05, Even Rouault <<a href="mailto:even.rouault@spatialys.com" target="_blank">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">
<div>
<p>Javier,</p>
<p>If you need a WKT2 with a coordinate operation, then you can
simply wrap any PROJ string expressing a coordinate operation like
the following:<br>
</p>
<p>$ projinfo "+proj=geogoffset +dh=5" -o WKT2:2019 -q<br>
<br>
CONVERSION["PROJ-based coordinate operation",<br>
METHOD["PROJ-based operation method: +proj=geogoffset +dh=5"]]<br>
</p>
<p>Of course only interoperable in the PROJ universe.</p>
<p>Otherwise using Transformation::createGeographic3DOffsets() /
createGeographic2DWithHeightOffsets() could have been an option,
but if your source and target CRS aren't geographic, PROJ will
complain when getting the PROJ transformation string.<br>
</p>
<p>Even<br>
</p>
<div>Le 29/11/2021 à 16:53, Javier Jimenez
Shaw a écrit :<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>Thanks Even</div>
<div><br>
</div>
<div>Is there anything equivalent to that as Vertical CRS to use
in a Compound? I know it is not correct geodetically, but I
want it just as a WKT temporary object. I just need that PROJ
is able to understand it and use it in a transformation.<br>
</div>
<div>That is, given a horizontal CRS, I want to create a
compound (or anything equivalent) with a vertical offset (as
WKT2 if it makes things easier)</div>
<div><br>
</div>
<div>Thanks.<br>
</div>
<div>
<div>
<div dir="ltr">.___ ._ ..._ .. . ._.
.___ .. __ . _. . __.. ... .... ._ .__<br>
Entre dos pensamientos racionales <br>
hay infinitos pensamientos irracionales.<br>
<br>
</div>
</div>
<br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Mon, 1 Nov 2021 at 17:01,
Even Rouault <<a href="mailto:even.rouault@spatialys.com" target="_blank">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">
<div>
<p>Javier<br>
</p>
<div>Le 01/11/2021 à 13:32, Javier Jimenez Shaw a écrit :<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>Hi</div>
<div><br>
</div>
<div>I want to make a transformation (at the end an
operation::CoordinateOperation) that replaces the
geoid model with a local constant value.</div>
<div><br>
</div>
<div>In some cases there is public grid file for a geoid
model, but I can get a (constant) undulation value
(let's say 42.9m) in a (small) area of work. I would
like to include this undulation value in the
transformation.</div>
<div><br>
</div>
<div>How can I do that? is there any pipeline option for
that? (I do not see a way in <a href="https://proj.org/operations/transformations/vgridshift.html" target="_blank">https://proj.org/operations/transformations/vgridshift.html</a>)
Or a way to directly create the CoordinateOperation?</div>
</div>
</blockquote>
<p>You can use the <a href="https://proj.org/operations/transformations/geogoffset.html" target="_blank">https://proj.org/operations/transformations/geogoffset.html</a>
with the dh parameter. This is for example used for
transformation EPSG:15596<br>
</p>
<p>Even<br>
</p>
<blockquote type="cite">
<div dir="ltr">
<div><br>
</div>
<div>Thanks<br>
</div>
<div>
<div>
<div dir="ltr">.___ ._ ..._ .. . ._. .___ .. __ .
_. . __.. ... .... ._ .__<br>
Entre dos pensamientos racionales <br>
hay infinitos pensamientos irracionales.<br>
<br>
</div>
</div>
</div>
</div>
<br>
<fieldset></fieldset>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr"><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><font color="#999999">Glen Rice</font></div><div><font color="#999999">National Bathymetric Source</font></div><div dir="ltr"><font color="#999999"><span style="font-size:12.8px">Hydrographic Systems and Technology Branch</span><br></font></div><div dir="ltr"><font color="#999999">Office of Coast Survey / Coast Survey Development Laboratory</font></div></div></div></div></div></div></div></div>