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

[Chris Crook]

Thanks for adding this Martin ... this is indeed very relevant!  I've not yet been able to look at the WKT version 2 standard but will.

While I can see that "late binding" is an alternative to a pivot coordinate system, it seems to invite issues with non-uniqueness, depending on how it is implemented.  Are you able to point me to any references on this please?

Thanks
Chris
________________________________________
From: metacrs-bounces at lists.osgeo.org [metacrs-bounces at lists.osgeo.org] On Behalf Of Martin Desruisseaux [martin.desruisseaux at geomatys.fr]
Sent: 07 January 2015 22:22
To: metacrs at lists.osgeo.org
Subject: Re: [MetaCRS] Fwd: Re: [Proj] Time dependent coordinate        transformations

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


This message contains information, which may be in confidence and may be subject to legal privilege. If you are not the intended recipient, you must not peruse, use, disseminate, distribute or copy this message. If you have received this message in error, please notify us immediately (Phone 0800 665 463 or info at linz.govt.nz) and destroy the original message. LINZ accepts no responsibility for changes to this email, or for any attachments, after its transmission from LINZ. Thank You.