On Thu, Jan 5, 2012 at 4:28 PM, Pierluigi Santin Fintel <
p.san...@fintelengineering.it> wrote:
> Hi all!
> hope to find someone that could help me.
> I have a big raster (geotiff) georeferenced in EPSG:3003
>
> I've loaded it to geoserver everything is fine if I query the layer in WMS
> using 3003, but if I query the same layer using epsg 900913, the quality of
> the reprojection is very poor. I've adapted the proj parameters to correcly
> reproject 3003 to 900913 for my local area but while this works perfectly
> for vector data the result is instead very bad for rasters.
>
> Am i missing something?
>
I cannot be sure without looking at your data, but certainly there are a
couple of
things missing to get optimal quality in raster reprojection:
- be able to select the overview policy. It can be set via code, but it's
not exposed
anywhere in GeoServer. At the moment the code uses the "closest overview"
policy, which is a compromise between speed and quality.
There is another policy that always chooses the overview with the higher
resolution
than the request, that one provides better results at the expense of
performance
- take into account the reprojection expansion. The Google projection
expands
pixels in the south to north direction, Italy is north enough that the
expansion
starts to become visible. Long story short, to get good results we should
read
more pixels from the source than what we have in the final output image,
but right now we don't. We'd need an estimator that can determine how much
more of the input we should read (different projections expand the pixels
in different directions, and by different amounts depending on where on
the
earth you are using them).
Internally in my company we discussed these problems a few times already,
but so far failed to raise the funding necessary to turn the ideas into
actual code
Cheers
Andrea
--
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Ing. Andrea Aime
GeoSolutions S.A.S.
Tech lead
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