[Fwd: [postgis-devel] WKT Raster: GDAL or World file upper left coordinates]

[Mateusz Loskot]

Hi,

I'm forwarding Pierre's post sent to PostGIS list about
handling georeferencing in WKT Raster. This is also related to GDAL, as
Pierre asks about GDAL.

Perhaps someone could help to explain it.

-------- Original Message --------
Subject: [postgis-devel] WKT Raster: GDAL or World file upper left
coordinates
Date: Wed, 4 Mar 2009 18:10:12 -0500
From: Pierre Racine <Pierre.Racine at sbf.ulaval.ca>
Reply-To: PostGIS Development Discussion
<postgis-devel at postgis.refractions.net>
To: PostGIS Development Discussion <postgis-devel at postgis.refractions.net>

gdal2wktraster.py stores the GDAL version of the upper left corner
coordinate. This seems to be the real (or external) upper left corner.

World files (and WKT Raster) stores the "center" of the upper left pixel
which is not the same thing. rt_raster_envelope(raster) was implemented
this way. It add half of a pixelsize to get the BBOX of the raster. So
now it returns an envelop a bit too big.

We'll have to decide if we stick to GDAL specs or to World file specs.

Why does GDAL does not stick to the Word File specs? What are the pros
and cons of one way over the other?

Pierre

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-- 
Mateusz Loskot, http://mateusz.loskot.net
Charter Member of OSGeo, http://osgeo.org