<div dir="ltr">Reading some answers, I realized that the term "WGS84" is very polysemic. To see the different meanings (are there more?), let's use this WKT:<div><br></div><div><font face="monospace">projinfo EPSG:32632 -o WKT1:GDAL -q</font></div><div><font face="monospace"><br>PROJCS["WGS 84 / UTM zone 32N",<br> GEOGCS["WGS 84",<br> DATUM["WGS_1984",<br> SPHEROID["WGS 84",6378137,298.257223563,<br> AUTHORITY["EPSG","7030"]],<br> AUTHORITY["EPSG","6326"]],<br> PRIMEM["Greenwich",0,<br> AUTHORITY["EPSG","8901"]],<br> UNIT["degree",0.0174532925199433,<br> AUTHORITY["EPSG","9122"]],<br> AUTHORITY["EPSG","4326"]],<br> PROJECTION["Transverse_Mercator"],<br> PARAMETER["latitude_of_origin",0],<br> PARAMETER["central_meridian",9],<br> PARAMETER["scale_factor",0.9996],<br> PARAMETER["false_easting",500000],<br> PARAMETER["false_northing",0],<br> UNIT["metre",1,<br> AUTHORITY["EPSG","9001"]],<br> AXIS["Easting",EAST],<br> AXIS["Northing",NORTH],<br> AUTHORITY["EPSG","32632"]]</font><br><div><br></div><div>We see that WGS84 can be:</div><div> - Spheroid/Ellipsoid (EPSG:7030)</div><div> - Datum (EPSG:6320). A datum ensemble in this case (more about that later)</div><div> - The prefix of all the 6 datums members of that datum ensemble EPSG:6320, like WGS84(transit) or WGS84(G1762)</div><div> - Geographic CRS (EPSG:4326)</div><div> - The prefix of many projected CRS. All those that have EPSG:4326 as the base geographic crs, like "WGS 84 / UTM zone 32N"</div><div><br></div><div>In addition to that, I met some people using it wrongly</div><div> - Some people use it to refer to any UTM projection over WGS84 (the one that affects them). They say "WGS84" instead of "WGS84 / UTM zone 30N"</div><div> - As the "one and only" lat-long system</div><div><br></div><div>The accuracy problem I mentioned in previous emails is due to the fact that the datum "WGS_1984" is a datum ensemble, that produces that you are not sure about which one are you talking about:<br><div><a href="https://epsg.org/datum_6326/World-Geodetic-System-1984-ensemble.html">https://epsg.org/datum_6326/World-Geodetic-System-1984-ensemble.html</a></div><div>(actually EPSG marks it with an accuracy of 2 m)</div><div>The same happens to the associated geographic crs, WGS84 EPSG:4326. And that "pollutes" all the projected crs that use EPSG:4326 as the geographic crs.</div><div><br></div><div>The last member of that ensemble, WGS84(G1762), has a geographic crs, EPSG:9057. However, there are no projected crs on it in EPSG.</div><div><br></div><div>Cheers,</div><div>Javier<br clear="all"><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature">.___ ._ ..._ .. . ._. .___ .. __ . _. . __.. ... .... ._ .__<br>Entre dos pensamientos racionales <br>hay infinitos pensamientos irracionales.<br><br></div></div><br></div></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sun, 18 Apr 2021 at 16:37, Lesparre, Jochem <<a href="mailto:Jochem.Lesparre@kadaster.nl">Jochem.Lesparre@kadaster.nl</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">
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<p class="MsoNormal">Duncan wrote:</p>
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<p class="MsoNormal"><span lang="EN-GB">> As an onlooker, I have a question: what is UTM/WGS84 intended to mean?
</span>Is it (A) the UTM projection using the WGS84 ellipsoid<u></u><u></u></p>
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<p class="MsoNormal"><span lang="EN-GB">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?
</span>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.<u></u><u></u></p>
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<p class="MsoNormal"><u></u> <u></u></p>
<p class="MsoNormal"><span lang="EN-GB">Duncan, I think WGS84-UTM is normally intended to mean both A and B so it is using a datum of WGS84 realisation and the WGS84 ellipsoid. According to ISO and EPSG de ellipsoid is part of the datum, so in that case the
answer A and B is the same as just B. <u></u><u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB"><u></u> <u></u></span></p>
<p class="MsoNormal"><span lang="EN-GB">Jochem <u></u><u></u></span></p>
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