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

Simon Perkins sy at perkins.net
Tue Nov 14 20:51:37 EST 2006

TIFF has some pretty serious file size limitations so wouldn't be good 
for these kinds of large rasters. I'm not familiar with TILEINDEX, but 
is this a MapServer related thing? Is that applicable to local image 
storage on the desktop?

I think the GeoQuadTree idea is interesting - it doesn't rely on large 
file support on the OS (not that that's a serious problem for any modern 
OSes), and dealing with lots of small files could be more efficient than 
one large file in some cases I would think.

As for PNG vs JPEG, it depends on whether you're happy to accept lossy 
compression or not. For many applications, customers are averse to 
losing any resolution. It might make sense to make the underlying file 
format in GeoQuadTree flexible acording to application. Actually, I'd 
prefer to see a format that can handle multispectral files - PNG and 
JPEG are both limited to 1 or 3 bands, aren't they? Or are multiple 
bands stored as separate grayscale images?

I would guess that with very large rasters, some sort of pyramid scheme 
becomes important in addition to the tiling, so that if you just want to 
get an overview of the whole image, you don't have to read every single 
file. Does GeoQuadTree handle that?

But, Ed is right that storing very large rasters is a not a new problem. 
So, what do people do? I guess that at the high end, outfits like Google 
Earth use a spatial database to organize multiple individual raster 
files and then stich them together. Could somebody outline the solution 
used by the Virtual Terrain project?



Ed McNierney wrote:
> Jordi -
> You said you wanted to "avoid the use of tile indexes or catalogues of 
> images", but isn't that exactly what your XML catalogue/index does?  
> It seems that the GeoQuadTree format is a different form of that same 
> sort of structure.  There are several different ways of doing this 
> now, including the TILEINDEX mechanism, tiled TIFF files, etc.  I'm 
> sure there are limitations to each, but I'm not sure that yet another 
> tiling scheme will help.
> In particular, PNG is not the best format for all images, and it's 
> important to support other encoding mechanisms, especially JPEG.  
> Photographic images are huge when stored in PNG format, and JPEG is 
> usually a much better choice.  Conversely, scanned line art and 
> synthetic images generally compress and store better as PNG images.
>     - Ed
> Ed McNierney
> President and Chief Mapmaker
> TopoZone.com / Maps a la carte, Inc.
> 73 Princeton Street, Suite 305
> North Chelmsford, MA  01863
> ed at topozone.com
> (978) 251-4242
> ------------------------------------------------------------------------
> *From:* gdal-dev-bounces at lists.maptools.org 
> [mailto:gdal-dev-bounces at lists.maptools.org] *On Behalf Of *Brent Fraser
> *Sent:* Tuesday, November 14, 2006 3:05 PM
> *To:* Jordi Gilabert Vall; gdal-dev at lists.maptools.org
> *Subject:* Re: [Gdal-dev] GeoQuadTree - an open format for 
> storinggeoreferencedimages
> For those interested tiling,
>   There is similar tiling related discussion/work going on at:
>         http://lists.eogeo.org/mailman/listinfo/tiling (do they have a 
> web page?)
>     and
>             http://www.stereofx.org/terrain.html, implemented in 
> http://vterrain.org/, particularly VTBuilder 
> (http://vterrain.org/Doc/VTBuilder/overview.html)
> Brent Fraser
>     ----- Original Message -----
>     *From:* Jordi Gilabert Vall <mailto:jordi at geoquadtree.org>
>     *To:* gdal-dev at lists.maptools.org
>     <mailto:gdal-dev at lists.maptools.org>
>     *Sent:* Tuesday, November 14, 2006 3:25 AM
>     *Subject:* [Gdal-dev] GeoQuadTree - an open format for storing
>     georeferencedimages
>     Hi,
>     Some time ago I needed the retrieval from very large georeferenced
>     raster images in a OGC WMS server, and I wanted to avoid the use
>     of tile indexes or catalogues of images, neither a database. I
>     started thinking of an open format for storing arbitrarily large
>     georeferenced images. I named this format "GeoQuadTree", as it
>     would be based on a quadtree of rectangular tiles, each in PNG
>     format on the filesystem, in a simple hierarchical structure of
>     folders. I wrote a command line utility for creating it, importing
>     from PNG/JPEG/TIFF and exporting to PNG/JPEG/TIFF/GDAL. I also
>     wrote a GDAL driver for this format. I tested successfully with my
>     own WMS server software, and on MapServer compiled with GDAL
>     support. It worked very well on Blue Marble Next Generation at a
>     resolution of 15 arc-seconds, i.e. 86400x43200 pixels.
>     You can find more information on the project web site:
>     http://geoquadtree.org/ <http://geoquadtree.org/>
>     I'm testing the release 1.0.0, you can test it on the subversion
>     repository if you want (I haven't packaged it yet).
>     I think it's a useful format, open, very easy to use, and very
>     efficient (in terms of response time).
>     Do you think it could be useful for you ? Would you like to
>     include it on GDAL's next release ?
>     jordi at geoquadtree org
>     ------------------------------------------------------------------------
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