[Gdal-dev] hatches rendering issues

[Frank Warmerdam]

Eric Lemoine wrote:
> If my original image is 1/5000 and if I use <gdaladdo file.tif 2 4>,
> is MapServer going to do its own downsampling? I was expecting
> MapServer to rely on the overviews created by gdaladdo and do nothing
> more.

Eric,

Generally speaking MapServer will work from the overview corresponding to
the resolution of the map request.  If there is no direct correspondence
it will work from the closest *higher resolution* overview.

Things are also complicated by the fact that in some modes (ie. AVERAGE
resampling, reprojecting) MapServer requests the source data somewhat
oversampled and downsamples/warps from that.  So you may actually end up
loading a higher resolution overview than you would otherwise expect.

If the overview level requested for "normal" views does not correspond
to the resolution of an overview, downsampling must still be done by
MapServer.

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