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<p>Hello all<br>
</p>
<p>I'm not sure if the following is relevant, but just in case:<br>
</p>
<p>The EPSG database already includes time-dependent coordinate
transformation methods in the form of Bursa-Wolf parameters with
14 terms. They are <tt>OperationMethod</tt> EPSG:1053 and
EPSG:1056 [1]. Some open source GIS software already implement (at
least partially) those methods, for example Apache Spatial
Information System (SIS) [2].<br>
</p>
<p>While EPSG recognizes that using a pivot Coordinate Reference
System (WGS84 or any other) is a common approach, they recommend
to avoid this approach if possible. Indeed, the <tt>TOWGS84</tt>
keyword is now deprecated in the new <i>Well Known Text</i> (WKT)
version 2 standard, developed at OGC/ISO as the ISO 19162
international standard [3]. Attaching transformation information
to a CRS is what EPSG calls "<i>Early binding approach</i>". EPSG
recommends instead the "<i>Late binding approach</i>", which is to
search transformation information in a database for (<i>sourceCRS</i>,
<i>targetCRS</i>) pairs.<br>
</p>
<p>The Open Geospatial Consortium (OGC) just started recently
discussions in a working group about time-dependent
transformations. This discussion was trigged by meteorologists for
vertical coordinate transformations between pressure (kPa) and
metres, where the pressure at the ground level change every day.
Maybe this discussion could be extended to the cases discussed in
this thread.<br>
</p>
Martin<br>
<br>
<br>
<br>
[1] <a class="moz-txt-link-freetext" href="http://epsg-registry.org">http://epsg-registry.org</a> (click on "<i>retrieve by code</i>" and
enter "1053" in the search box) <br>
[2]
<a class="moz-txt-link-freetext" href="http://sis.apache.org/apidocs/org/apache/sis/referencing/datum/TimeDependentBWP.html">http://sis.apache.org/apidocs/org/apache/sis/referencing/datum/TimeDependentBWP.html</a><br>
[3] <a class="moz-txt-link-freetext" href="http://www.iso.org/iso/catalogue_detail.htm?csnumber=63094">http://www.iso.org/iso/catalogue_detail.htm?csnumber=63094</a><br>
<br>
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