[Gdal-dev] Building a Projection Dialog

[Frank Warmerdam]

Ari Jolma wrote:
> Diaren kirjoitti:
>> That would solve part of the dialog... the next part is listing / editing
>> the supported Datums. There are various files in the data folder namely:
>> coordinate_axis.csv
>> ...
>>   
> 
> Diaren,
> 
> I'm not an authoritative source (Frank is), but let me try. The csv 
> files are key files, which I suppose you need to read in by yourself 
> (there is code for parsing csv in GDAL though but that is not exposed to 
> swig). They are copied to GDAL from libgeotiff, take a look at 
> https://svn.osgeo.org/metacrs/geotiff/trunk/libgeotiff/csv/ The README 
> file explains how they are made from EPSG database.

Diaren,

Ari is quite right.  I'd add that the gcs.csv file would likely be the
one you want to focus on for letting the user select a geographic coordinate
system.  This is the set of EPSG geographic coordinate systems.   For each
GCS it holds information on the EPSG GCS code, the prime meridian,
datum, ellipsoid and, in some cases, a suggested datum shift transformation
to WGS84.

You could actually try and let people compose geographic coordinate systems
from their own selection of datum, prime meridian and ellipsoid but I'm
not really sure you will get much additional value.

One think you *should* do is allow overriding/providing TOWGS84 datum
shift values since the provided set is quite incomplete and often people
will need to use values more appropriate to their work area.

The area is somewhat complex and you will likely need to do some research
to get a good grasp on the topic.  The gcs.csv file is built from the
EPSG database, but by denormalizing a variety of EPSG tables to produce
collected GCS information in a single record.

One aspect I have traditionally ignored is "area of use".  In theory you
could utilize this field to show a restricted set of GCSes likely to be
of interest to people in a limited region.  I have no specific advice on
this.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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