[Gdal-dev] JPEG Tiling?

[Frank Warmerdam]

On 4/29/05, Justin Thomas <justin.w.thomas at gmail.com> wrote:
> I'm fairly new to the geospatial imagery world, so please forgive me
> if this question is totally in left field.  I have made a few test
> programs using GDAL and OGR and so far I have been very pleased with
> how easy it was to do fairly complex tasks.
> 
> I read the JPEG driver documentation, but I could not see how to load
> a set of tiled JPG and JGW files so that I can use GDAL to provide a
> window of pixels for the combined area.
> 
> Is there is a simple workaround or could somone please point me to a
> website with a discussion on the limitations on the different formats?

Justin,

Are you wanting to be able to treat a bunch of individual JPEG
files as single virtual GDALDataset?   There is no built-in support
for doing that; however, there are a few approaches.

The most obvious is to create a .vrt (virtual) dataset referencing
all the individual tiles.   the .vrt file is an XML file that can list
a bunch of other GDAL supported files and listing where they fit
into a virtual file.  This is described at:

   http://www.gdal.org/gdal_vrttut.html

There is also a script, gdal_merge.py, that can be used to quickly
build a mosaic from a set of georeferenced files.  So you could create
a real mosaic from a bunch of jpegfiles with world files using it.  

I would be sort of nice to have a gdal_merge.py variation that
just created a virtual file representing essentially the same result
but without copying data; however, I have not built such a utility.

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