WMS: non square pixels performance

[Frank Warmerdam]

Bart van den Eijnden (OSGIS) wrote:
> Hi list,
> 
> can one expect a performance drop of about 1000% for WMS images using non
> square pixels? That is at least what we are experiencing. Is this normal and
> to be expected?
> 
> Fast image: < 1 second:
> &bbox=0,300000,300000,600000&width=320&height=320
> 
> Slow image: 10 seconds:
> &bbox=0,300000,300000,625000&width=320&height=320

Bart,

When non-square pixels are used, MapServer switches from the optimized
"let GDAL do all downsampling" logic to going through the general
image reprojection logic for input imagery.  That will be substantially
slower, though I'm surprised that it would be 10 times slower.

If you can isolate a demonstration of this that I can reproduce, I might
be able to figure out why it is so much slower.

Best regards,
-- 
---------------------------------------+--------------------------------------
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    | President OSGeo, http://osgeo.org