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<p>Henning,</p>
<p>both GDA94 and GDA2020 are "static" CRS, that is coordinates are
not time dependent in any of those, so it is expected that
specifying the coordinate epoch in such transformations has no
impact.</p>
<p>There are known time-dependent transformation between GDA94 and
ITRF2014 or GDA2020 and ITRF2014. Your GPS probably outputs
coordinates in WGS 84 (G1762) (or maybe another realization), but
you may perhaps try to assume that ITRF2014 and that WGS 84 are
equivalent for your purposes.</p>
<p>Then you can for example use</p>
<p>$ echo 300000 6000000 0 2020.5 | cs2cs -d 8 EPSG:28356 EPSG:9000</p>
<p>-36.12408288 150.77761389 -0.09245914 2020.5</p>
<p><br>
</p>
<p>You can also build a "ITRF2014 / Map Grid of Australia zone 56"
projection by using
"urn:ogc:def:crs,crs:EPSG::9000,cs:EPSG::4400,coordinateOperation:EPSG::17356"</p>
<p>(EPSG:9000 referes to the geographic CRS ITRF2014, EPSG:4400 to
the easting/northing coordinate system, and EPSG:17356 to the
conversion method for MGA56)</p>
<p>Then</p>
<p>$ echo 300000 6000000 0 2020.5 | cs2cs -d 8 EPSG:28356
urn:ogc:def:crs,crs:EPSG::9000,cs:EPSG::4400,coordinateOperation:EPSG::17356<br>
300000.44233932 6000001.44797768 -0.09245914 2020.5<br>
<br>
</p>
<p>(you might get slightly different results if the GDA94 to GDA2020
grid is present)</p>
<p>Even<br>
</p>
<div class="moz-cite-prefix">Le 04/10/2021 à 21:16,
<a class="moz-txt-link-abbreviated" href="mailto:henning@kaarta.com">henning@kaarta.com</a> a écrit :<br>
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<p class="MsoNormal">Hello,<o:p></o:p></p>
<p class="MsoNormal">I have a set of ground control points
provided by a surveyor in Australia that were created in June
2020.<o:p></o:p></p>
<p class="MsoNormal">They are expressed in MGA94 / Zone 56 CRS,
which I believe is EPSG:28356.<o:p></o:p></p>
<p class="MsoNormal">I would like to convert these points to
MGA2020 (EPSG:7856) and relate them to actual data coming from
a Trimble GPS today.<o:p></o:p></p>
<p class="MsoNormal">Using PROJ7, I am able to get transformed
values between MGA94 and MGA2020 that reflect the displacement
of the Australian continent between those CRSs, e.g. (using
some round numbers to illustrate here)<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">echo 300000 6000000 0 | cs2cs
+init=epsg:28356 +to +init=epsg:7856 -d 3<o:p></o:p></p>
<p class="MsoNormal">300000.435 6000001.421 0.000<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">However, in comparing the results to
current readings from the GPS, I see they’re off by what may
be the continental drift that’s occurred in the last 15 months
– about 8 cm northeast.<o:p></o:p></p>
<p class="MsoNormal">I know PROJ7 knows about time-dependent
transformations, I just can’t seem to figure out how to use
that to get my GCP coordinates in today’s MGA2020 grid. I’ve
naively tried<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">echo 300000 6000000 0 2020.5 | cs2cs
+init=epsg:28356 +to +init=epsg:7856 -d 3<o:p></o:p></p>
<p class="MsoNormal">300000.435 6000001.421 0.000
2020.5<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">but it comes up with the same numbers. <o:p></o:p></p>
<p class="MsoNormal">Do I need to construct a more elaborate
pipeline, and is this even something cs2cs can be used for?<br>
Any tips or tricks would be appreciated! As you might have
guessed, I’m pretty much a novice with PROJ7.<o:p></o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Henning Pangels<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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My software is free, but my time generally not.</pre>
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