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<p>Giacomo,</p>
<p>Coordinate transformations are definitely not a trivial subject,
so no worry not understanding what's going on here.</p>
<p>PROJ uses the content of its database to find, or infer,
coordinate transformations. Most of the content comes from the
EPSG database itself.</p>
<p>For RDN2008, there are 2 transformations available:</p>
<p>- one from RDN2008 to ETRS89 (EPSG:4258), with a null Helmert
transformation and a accuracy of 0 m. This is consistant with how
you described RDN2008, and this transformation has the comment
"RDN2008 is the second Italian realization of ETRS89"</p>
<p>- one from RDN2008 to WGS 84, which is the same null Helmert
transformation, copied from the above, but with a accuracy of 1 m
(due to WGS 84 being dynamic and moving over time compared to
plate fixed CRS such as RDN2008 or ETRS89)</p>
<p>The first one would be a good candidate, but PROJ doesn't know he
can use it, since there is no explicit transformation in its
database between ETRS89 and ETRF2000. That said in the database,
ETRS89 is modeled as a datum ensemble of the many ETRFxxxx
realizations, so potentially PROJ could use that information to
infer a null transformation between ETRS89 and ETRF2000 with the
accuracy of the datum ensemble (here 0.1 m) (we actually do that
manually for the WGS 84 datum ensemble vs its realizations, but
that should be generalized), and chain that together with the
RDN2008 to ETRS89 transformation.</p>
<p>In the meantime, you can customize your proj.db by adding the
following 2 records. Can be done with the sqlite3 command line
utility</p>
<p>$ sqlite3 proj.db<br>
</p>
<p>INSERT INTO "helmert_transformation"
VALUES('PROJ','ETRS89_TO_ETRF2000','ETRS89 to ETRF2000','Accuracy
0.1m, derived from ETRS89 datum ensemble
definition','EPSG','9603','Geocentric translations (geog2D
domain)','EPSG','4258','EPSG','9067',0.1,0,0,0,'EPSG','9001',NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,NULL,'',0);<br>
INSERT INTO "usage" VALUES(<br>
'PROJ',<br>
'ETRS89_TO_ETRF2000_USAGE',<br>
'helmert_transformation',<br>
'PROJ',<br>
'ETRS89_TO_ETRF2000',<br>
'EPSG','1298', -- Europe<br>
'EPSG','1024' -- unknown<br>
);</p>
<p>.quit</p>
<p>With that, you'll get<br>
</p>
<p>$ projinfo -s RDN2008 -t ETRF2000 <br>
Candidate operations found: 1<br>
-------------------------------------<br>
Operation No. 1:<br>
<br>
unknown id, RDN2008 to ETRS89 (1) + ETRS89 to ETRF2000, 0.1 m,
Italy - onshore and offshore; San Marino, Vatican City State.<br>
<br>
PROJ string:<br>
+proj=noop<br>
</p>
<p>Even<br>
<br>
</p>
<div class="moz-cite-prefix">Le 19/07/2022 à 03:02, Giacomo
Cappellini a écrit :<br>
</div>
<blockquote type="cite"
cite="mid:CABXJd1nWgMuwZMOUwRNSR9v-4cjs_vAdzpNZ2F3jszqO9+WG=A@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">
<div>Hello,</div>
<div><br>
</div>
<div>I'm generally new to working with CRS different from
EPSG:4326 <a class="gmail_plusreply"
id="gmail-m_2346281136540197199plusReplyChip-0"
moz-do-not-send="true">+</a> UTM and I'm facing some issues
while trying to use RDN2008, which is the official reference
system for Italy at current date.</div>
<div>Please excuse me if the question sounds trivial to experts,
but I can't figure out why there are no non-ballpark
operations to go from/to RDN2008 and ETRF2000 or ITRF2000.</div>
<div><br>
</div>
<div>Afaik, RDN2008 is ETRS89 realization ETRF2000 epoch 2008.0.<br>
</div>
<div><br>
</div>
<div>Proj Rel. 8.2.1, January 1st, 2022</div>
<div><br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">$
projinfo -s EPSG:6706 -t EPSG:9067 --spatial-test intersects
--grid-check none --hide-ballpark --summary<br>
Candidate operations found: 0</blockquote>
<div><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>$ projinfo -s EPSG:6706 -t EPSG:8997 --spatial-test
intersects --grid-check none --hide-ballpark --summary<br>
Candidate operations found: 0</div>
</blockquote>
<div><br>
</div>
<div>Thanks</div>
<div><br>
</div>
<div>G.C. <br>
</div>
</div>
<br>
<fieldset class="moz-mime-attachment-header"></fieldset>
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</pre>
</blockquote>
<pre class="moz-signature" cols="72">--
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My software is free, but my time generally not.</pre>
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