GDAL virtual raster file

[Frank Warmerdam]

On 4/14/05, Nuno Gil <nunoragil at gmail.com> wrote:
> Frank,
> Ok, so if I understand you correctly one layer calls the original
> full-res tiles and then another one call the overviews.
> My overview files have an "ovr" extension and when creating the index
> file for them I get

Nuno, 

The mapserver "overview" layer wouldn't be using the overviews
built for the full res files.  Those are automatically used by GDAL. 

The objective of using a separate layer in MapServer is so that
you can have an overview that is "all-in-one" file.  What is killing
you with showing overviews of 300 files worth of data is all the
per-file overhead.  This is modest for 1 or 5 files, but open 300 
GeoTIFF files, and parsing all the headers ends up being quite a
bit of work. 

So, the overview layer should refer to a single big overview at
a much reduced resolution from the original files.  The tricky
part is building this overview, as I mentioned before.  There are
a variety of approaches, but for my money the easiest is to use
Mapserver itself.  Do you need details on this process?  I have
never *actually* done it myself. 

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