[Mapserver-users] Double indexing?

[Frank Warmerdam]

Steve Lehr wrote:
> List:
> 
> Is their such a thing as double indexing.  I have some very large Image
> (TIFF/SID) files in a tileindex.  Can each of the large TIFFS have some sort
> of index on them to allow faster rendering within the picked TIFF?
> 
> Any examples and/or utility examples to make the indexes would be greatly
> appreciated.  For the winning tip there is beer involved!

Steve,

There is no equivelent to the shape file indexing supported by mapserver for
raster files.  However, it is generally implicit in the format drivers.
For instance, if you ask for a small rectangle out of a large tiled tiff
file, GDAL (as called by MapServer) will only read the tiles intersected
by the requested window.

So the issue is more about selecting appropriate formats, and organizations
of those formats for good performance.  The primarily levers are tiling
(to ensure local window requests are fast), and building overviews to ensure
that decimated overviews of large areas are fast.

My understanding of MrSID format is that the format, and GDAL driver for it
are supposed to load subareas, or overviews fast based on smarts in the
MrSID format, and the libraries provided with it.  I don't have much imperical
evidence on this yet, but we can work on that off the list.

Best regards,

-- 
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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    | Geospatial Programmer for Rent