[Gdal-dev] GeoQuadTree - an open format for storinggeoreferencedimages

Frank Warmerdam warmerdam at pobox.com
Wed Nov 15 13:50:11 EST 2006

Jordi wrote:
> Frank,
> I agree that the GeoQuadTree GDAL driver should be under the MIT/X 
> license used in the rest of the project.


Ah, cool.  Then inclusion should be no problem.  Lets make sure it
makes it in before 1.4.0 release.

> At first I included the CRS definition in the same XML metadata file, 
> but later I thought it would be more useful as a separate file, with 
> .prj extension. This CRS file IS the definition in Well Known Text 
> format, as is returned from PROJ.4 library. Do you think it would be 
> better to include it in the same XML metadata file ?

Ah.  I just read the FAQ entry on the format, which I don't think
mentions the CRS file.  A seperate .prj file with the wkt coordinate system
should be fine.

You say "in Well Known Text format, as returned from PROJ.4 library".
The well known text format is not used or produced by the PROJ.4 library
so either you are really using PROJ.4 definitions (not WKT) or you really
mean as returned by OGRSpatialReference.

WKT usually starts with PROJCS or GEOGCS while PROJ.4 strings include
something like +proj=.

I think we should be using WKT as it is not so software specific.

> I've started working on including the choice for JPEG, JPEG2000 or TIFF 
> as alternatives to PNG for the format of the tiles. I would like also to 
> support multi-bands with TIFF or with multiple PNGs/JPGs.


> You are absolutely right that sacrificing a RGB color for nondata is not 
> a good idea in JPEG.
> I don't know if I understand what you mean about a "standard tile 
> cache". I'm sorry that I didn't study enough the GDAL core, and I didn't 
> know about the block cache. I'll try to use it: I implemented my own 
> tile cache, but only as a consequence of my ignorance in GDAL internals.

This isn't a GDAL thing at all.  Various web obsessed folks from projects
like OpenLayers, ka-map, and others have been trying to hash out a standard
approach to web accessable tile caches such as those used by Google maps,
and WorldWind.  So that web tile caches could be shared more effectively
by different software packages.  I think the following urls capture some
of that planning/discussion/thinking though I haven't been following it
closely myself.


My thinking is that if they hammer this out it would be nice if the
geoquadtree cache format sitting on a web server would adhere to their
specification making it directly usable.  I don't know enough about this
to be sure if this is reasonable or not.

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/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org

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