<div dir="ltr"><div>As an onlooker, I have a question: what is UTM/WGS84 intended to mean? Is it (A) the UTM projection using the WGS84 ellipsoid</div><div>as a parameter, or (B)  is it meant to imply also that the coordinates are in a datum that is one of the several labelled WGS84? A is clear and completely unambiguous; B isn't, partly because it is subject to change as data are collected (not to mention plate motions). Data-dependence is also a problem with geoid models: it is why there are so many, after all.<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, Apr 18, 2021 at 2:51 AM 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">
  
    
  
  <div>
    <p>Yes, I assume that the large number of codes that should be
      created, and still for relatively marginal use cases, is what
      makes IOGP refrain from doing that.<br>
    </p>
    <p>What you describe is exactly the not so known OGC URN syntax for
      combined objects (see OGC 07-092r2, para 7.5.4 :
      <a href="https://urldefense.com/v3/__https://portal.ogc.org/files/?artifact_id=29533__;!!Mih3wA!W6E8KjQeH8H-OnMjrZ9cWSBnPkQEeS2Ow1ldMT0tZvbKVM5fTlD9r718H5HVjC4$" target="_blank">https://portal.ogc.org/files/?artifact_id=29533</a> )<br>
    </p>
    <p>For example for UTM 31N / WGS 84 (G1762), that is<br>
    </p>
    <p>urn:ogc:def:crs,crs:EPSG::9057,cs:EPSG::4400,coordinateOperation:EPSG::16031</p>
    <p>and you can use that with projinfo / proj_create()</p>
    <p>If you use that in GeoTIFF, what would be missing though is the
      coordinate epoch. You'll have to store it in a TIFF tag. There's
      no way in the GeoTIFF encoding itself to store it.<br>
    </p>
    <p>Even<br>
    </p>
    <div>Le 18/04/2021 Ã  09:20, Lesparre, Jochem
      via PROJ a Ã©crit :<br>
    </div>
    <blockquote type="cite">
      
      <div>
        <p class="MsoNormal"><span lang="EN-GB">This is indeed a major
            problem with (the way most software and people are using)
            EPSG. By just using EPSG CRS codes, one needs a unique EPSG
            CRS code for every possible combination of datum and
            projection. However, the number of possible combinations is
            way too large. I think, the solution is to split the datum
            definition (WGS84, WGS84G1762, ITRF2014, ETRF2000, etc.) and
            the projection definition (UTM, pseudomercator, LAEA, LCC,
            etc.). For the datum definition one can use the normal EPSG
            CRS codes. For the projection definition one could use the
            lesser known EPSG conversion codes, e.g. EPSG conversion
            code 16031 (<a href="https://urldefense.com/v3/__https://epsg.org/conversion_16031/UTM-zone-31N.html__;!!Mih3wA!W6E8KjQeH8H-OnMjrZ9cWSBnPkQEeS2Ow1ldMT0tZvbKVM5fTlD9r718m8HlkqY$" target="_blank">https://epsg.org/conversion_16031/UTM-zone-31N.html</a>)
            for UTM zoned 31N. Isn’t this the approach used in WKT
            strings?</span></p>
        <p class="MsoNormal"><span lang="EN-GB"> </span></p>
        <p class="MsoNormal"><span lang="EN-GB">Jochem
          </span></p>
        <p class="MsoNormal"><span lang="EN-GB"> </span></p>
        <div>
          <div>
            <p class="MsoNormal"><b><span lang="EN-US">From:</span></b><span lang="EN-US"> PROJ <a href="mailto:proj-bounces@lists.osgeo.org" target="_blank"><proj-bounces@lists.osgeo.org></a>
                <b>On Behalf Of </b>Noel Zinn (cc)<br>
                <b>Sent:</b> zaterdag 17 april 2021 23:59<br>
                <b>To:</b> Javier Jimenez Shaw
                <a href="mailto:j1@jimenezshaw.com" target="_blank"><j1@jimenezshaw.com></a><br>
                <b>Cc:</b> proj <a href="mailto:PROJ@lists.osgeo.org" target="_blank"><PROJ@lists.osgeo.org></a><br>
                <b>Subject:</b> Re: [PROJ] World UTM in a proper datum</span></p>
          </div>
        </div>
        <p class="MsoNormal"> </p>
        <div>
          <div>
            <div>
              <p class="MsoNormal"><span>We really need two codes, don’t
                  we?  One for the geographical datum (ITRF2014 in
                  GRS80, which is EPSG:7789 in your case) and one for
                  the projection UTM in GRS80 (which, I guess, doesn’t
                  exist), perhaps an EPSG architecture problem.  To be
                  frank, your expectation that the EPSG do for ITRF2014
                  what it’s done for WGS84/UTM is unrealistic.  Add
                  ITRF2008 and so on, how many combinations would that
                  be?</span></p>
            </div>
            <div>
              <p class="MsoNormal"><span> </span></p>
            </div>
            <div>
              <div>
                <div>
                  <p class="MsoNormal"><span> </span></p>
                </div>
                <div>
                  <div>
                    <p class="MsoNormal"><b><span>From:</span></b><span>
                        <a href="mailto:j1@jimenezshaw.com" title="j1@jimenezshaw.com" target="_blank">Javier Jimenez Shaw</a>
                      </span></p>
                  </div>
                  <div>
                    <p class="MsoNormal"><b><span>Sent:</span></b><span>
                        Saturday, April 17, 2021 3:56 PM</span></p>
                  </div>
                  <div>
                    <p class="MsoNormal"><b><span>To:</span></b><span>
                        <a href="mailto:ndzinn@comcast.net" title="ndzinn@comcast.net" target="_blank">Noel Zinn (cc)</a>
                      </span></p>
                  </div>
                  <div>
                    <p class="MsoNormal"><b><span>Cc:</span></b><span>
                        <a href="mailto:PROJ@lists.osgeo.org" title="PROJ@lists.osgeo.org" target="_blank">proj</a> </span></p>
                  </div>
                  <div>
                    <p class="MsoNormal"><b><span>Subject:</span></b><span>
                        Re: [PROJ] World UTM in a proper datum</span></p>
                  </div>
                </div>
              </div>
              <div>
                <p class="MsoNormal"><span> </span></p>
              </div>
            </div>
            <div>
              <div>
                <p class="MsoNormal"><span>Hi Noel, </span></p>
                <div>
                  <p class="MsoNormal"><span>If I am the only user of
                      the data, I can do that (and whatever I want). But
                      if I have to produce accurate data processed by
                      somebody else, I fall into the hole of vagueness
                      of WGS84. For instance, if I create a precise
                      GeoTIFF and I want to tag it with an EPSG, using
                      EPSG:326XX is... vague. Or a GCP, or anything
                      else. There are several alternatives for the
                      geographic crs.</span></p>
                </div>
                <div>
                  <p class="MsoNormal"><span>I know I can apply UTM over
                      ITRF2014 (GDAL does it easily). But there is no
                      EPSG code for that.</span></p>
                </div>
                <div>
                  <div>
                    <p class="MsoNormal"><span> </span></p>
                  </div>
                  <div>
                    <div>
                      <p class="MsoNormal"><span>.___ ._ ..._ .. . ._. 
                          .___ .. __ . _. . __..  ... .... ._ .__<br>
                          Entre dos pensamientos racionales <br>
                          hay infinitos pensamientos irracionales.</span></p>
                    </div>
                  </div>
                  <div>
                    <p class="MsoNormal"><span> </span></p>
                  </div>
                </div>
              </div>
              <div>
                <p class="MsoNormal"><span> </span></p>
              </div>
              <div>
                <div>
                  <p class="MsoNormal"><span>On Sat, 17 Apr 2021 at
                      22:24, Noel Zinn (cc) <<a href="mailto:ndzinn@comcast.net" target="_blank">ndzinn@comcast.net</a>>
                      wrote:</span></p>
                </div>
                <blockquote>
                  <div>
                    <div>
                      <div>
                        <p class="MsoNormal"><span>Unlike an
                            empirically-derived datum transformation
                            (e.g. WGS <> ITRF), which can have
                            different levels of "accuracy" depending how
                            it was derived, a map projection (lat/lon
                            <> N/E) is defined mathematically and
                            is precise, i.e. without error.  Having said
                            that, there are better and worse algorithms
                            for UTM, but that's not the question you're
                            asking.  In a datum transformation sense UTM
                            will always be as (and only as) "accurate"
                            as the geographicals you convert to N/E.
                            Â So, use EPSG:326XX and EPSG327XX, but plug
                            in your precise geographicals. Â </span></p>
                        <div>
                          <div>
                            <div>
                              <p class="MsoNormal"><span> </span></p>
                            </div>
                            <div>
                              <div>
                                <p class="MsoNormal"><b><span>From:</span></b><span>
                                    <a href="mailto:j1@jimenezshaw.com" title="j1@jimenezshaw.com" target="_blank">Javier
                                      Jimenez Shaw</a>
                                  </span></p>
                              </div>
                              <div>
                                <p class="MsoNormal"><b><span>Sent:</span></b><span>
                                    Saturday, April 17, 2021 2:44 PM</span></p>
                              </div>
                              <div>
                                <p class="MsoNormal"><b><span>To:</span></b><span>
                                    <a href="mailto:PROJ@lists.osgeo.org" title="PROJ@lists.osgeo.org" target="_blank">
                                      proj</a> </span></p>
                              </div>
                              <div>
                                <p class="MsoNormal"><b><span>Subject:</span></b><span>
                                    [PROJ] World UTM in a proper datum</span></p>
                              </div>
                            </div>
                          </div>
                          <div>
                            <p class="MsoNormal"><span> </span></p>
                          </div>
                        </div>
                        <div>
                          <div>
                            <p class="MsoNormal"><span>Hi </span></p>
                            <div>
                              <p class="MsoNormal"><span> </span></p>
                            </div>
                            <div>
                              <p class="MsoNormal"><span>Maybe there is
                                  a better place to talk about this, but
                                  I do not know which one. I hope
                                  somebody from EPSG is reading this,
                                  and may give me a clue.</span></p>
                            </div>
                            <div>
                              <p class="MsoNormal"><span> </span></p>
                            </div>
                            <div>
                              <p class="MsoNormal"><span>We have talked
                                  many times about the lack of accuracy
                                  of WGS84 (EPSG:4326), the datum
                                  ensemble, etc.</span></p>
                            </div>
                            <div>
                              <p class="MsoNormal"><span>The problem is
                                  that I miss an accurate equivalent of
                                  the projected family "WGS84 / UTM zone
                                  XXY"(EPSG:326XX and EPSG327XX) for XX
                                  between 1 and 60 and Y is N or S. It
                                  would be nice something similar (a
                                  worldwide projected CRSs on UTM), but
                                  over a proper accurate and well
                                  defined geographic CRS (ITRF2014,
                                  WGS84(G1762), etc).</span></p>
                            </div>
                            <div>
                              <p class="MsoNormal"><span> </span></p>
                            </div>
                            <div>
                              <p class="MsoNormal"><span>Do you know if
                                  there is any plan? Or do they exist
                                  and I was not able to find them?</span></p>
                            </div>
                            <div>
                              <p class="MsoNormal"><span> </span></p>
                            </div>
                            <div>
                              <p class="MsoNormal"><span>Thanks.<br>
                                </span></p>
                              <div>
                                <div>
                                  <p class="MsoNormal"><span>.___ ._
                                      ..._ .. . ._.  .___ .. __ . _. .
                                      __..  ... .... ._ .__<br>
                                      Entre dos pensamientos racionales
                                      <br>
                                      hay infinitos pensamientos
                                      irracionales.</span></p>
                                </div>
                              </div>
                            </div>
                          </div>
                          <div class="MsoNormal"><span>
                              <hr width="100%">
                            </span></div>
                          <p class="MsoNormal"><span>_______________________________________________<br>
                              PROJ mailing list<br>
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                        </div>
                      </div>
                    </div>
                  </div>
                </blockquote>
              </div>
            </div>
          </div>
        </div>
      </div>
      <br>
      <br>
      Disclaimer:<br>
      De inhoud van dit bericht is uitsluitend bestemd voor
      geadresseerde.<br>
      Gebruik van de inhoud van dit bericht door anderen zonder
      toestemming van het Kadaster<br>
      is onrechtmatig. Mocht dit bericht ten onrechte bij u terecht
      komen, dan verzoeken wij u<br>
      dit direct te melden aan de verzender en het bericht te
      vernietigen.<br>
      Aan de inhoud van dit bericht kunnen geen rechten worden ontleend.<br>
      <br>
      Disclaimer:<br>
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      addressee only.<br>
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      <br>
      <fieldset></fieldset>
      <pre>_______________________________________________
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</pre>
    </blockquote>
    <pre cols="72">-- 
<a href="https://urldefense.com/v3/__http://www.spatialys.com__;!!Mih3wA!W6E8KjQeH8H-OnMjrZ9cWSBnPkQEeS2Ow1ldMT0tZvbKVM5fTlD9r718aCkmz9c$" target="_blank">http://www.spatialys.com</a>
My software is free, but my time generally not.</pre>
  </div>

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</blockquote></div>