[Proj] EPSG 7.9 Upgrade in Trunk

[Mikael Rittri]

Not a prompt reply, but anyway: 

I noticed that for the British datum OSGB 1936, gcs.csv in the libgeotiff trunk ( http://trac.osgeo.org/geotiff/browser/trunk/libgeotiff/csv ) uses 
the 3-parameter datum shift 

        EPSG:1195, "OSGB 1936 to WGS 84(1)", accuracy 21 m. 

I would have expected the more accurate 7-parameter datum shift

        EPSG:1314, "OSGB 1936 to WGS 84(6), accuracy 2 m. 

This is a special case of the ticket 

        http://trac.osgeo.org/geotiff/ticket/33

and since the general case won't be fixed, I suggest that OSGB 1936
needs special treatment (in datum_shift_pref.csv).

> New "preferred datum shift selection" rules are also in place which
> will give preference to 7 parameter datum shifts over 3 parameter 
> datum shifts 

You mean that some 7 parameter datum shifts are listed as preferred
in datum_shift_pref.csv ?  Because in build_pcs.py, I couldn't see
that 7-parameter shifts are preferred over 3-parameter shifts in general (but maybe I missed it).

Best regards,

Mikael Rittri
Carmenta
Sweden
http://www.carmenta.com

-----Original Message-----
From: proj-bounces at lists.maptools.org [mailto:proj-bounces at lists.maptools.org] On Behalf Of Frank Warmerdam
Sent: Thursday, September 29, 2011 9:04 AM
To: PROJ.4 and general Projections Discussions; GeoTIFF; gdal-dev
Subject: [Proj] EPSG 7.9 Upgrade in Trunk

Folks,

I have upgraded libgeotiff, PROJ.4 and GDAL with EPSG definitions regenerated
from the EPSG 7.9 database.  New "preferred datum shift selection" rules are
also in place which will give preference to 7 parameter datum shifts over
3 parameter datum shifts are also in place causing a fair amount of churn
in the definitions.

The updates are in "trunk" for each of the projects.  I plan to produce
libgeotiff and PROJ.4 release candidates soon with the new definitions
so if you think you might have objections please investigate and speak
up promptly.

Best regards,
-- 
---------------------------------------+--------------------------------------
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/warmerda
and watch the world go round - Rush    | Geospatial Software Developer

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