[MetaCRS] Fwd: Re: [Proj] Time dependent coordinate transformations

[Martin Desruisseaux]

Hello all

I'm not sure if the following is relevant, but just in case:

The EPSG database already includes time-dependent coordinate
transformation methods in the form of Bursa-Wolf parameters with 14
terms. They are OperationMethod 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].

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 TOWGS84 keyword is now deprecated in
the new /Well Known Text/ (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 "/Early binding approach/". EPSG
recommends instead the "/Late binding approach/", which is to search
transformation information in a database for (/sourceCRS/, /targetCRS/)
pairs.

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.

        Martin



[1] http://epsg-registry.org (click on "/retrieve by code/" and enter
"1053" in the search box)
[2]
http://sis.apache.org/apidocs/org/apache/sis/referencing/datum/TimeDependentBWP.html
[3] http://www.iso.org/iso/catalogue_detail.htm?csnumber=63094

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