On Thu, Apr 23, 2015 at 12:27 AM, Castrén Antti <
Antti.Castren@anonymised.com> wrote:
Hello all,
How does Geoserver reproject rasters by default? I'm interested in what
kind of interpolation method is used, and is there a possibility to choose
that in UI (or somewhere else)?
Nearest neighbor, you can choose it from the WMS settings panel
Another question is how the cell size / cell count issue is taken care of?
In our current case the source WMS server has layers natively in an UTM
projection (EPSG:3067) and we need to reproject a layer to a normal
Mercator projection (EPSG:3395). In theory there should be two steps, first
from UTM to ellipsoid and then from ellipsoid to Mercator. In the first
step the cell would be distorted from a square to rectangular ring arc
segment. The second step would just change the scale more or less.
We build the full math of the transformation and apply it in one step. If
the distortion is really high, we apply it as is (slow), otherwise we
search for a piecewise
affine transformation (grid based) so that the error of applying the
simplified one is less than 0.3 of the output pixels (thus, not visible),
and gain a significant
speedup by doing so.
The overall code around the transformation (affine transforms before and
after it to scale the data to fit the requested resolution) has been
changing
over time, so you'll get different results depending on the geoserver
version you're using.
I suggest you try the devel branch, it has the latest version, should be
the one that induces the least amount of resample operations from
source to output:
http://ares.boundlessgeo.com/geoserver/master/
Cheers
Andrea
--
GeoServer Professional Services from the experts! Visit
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Ing. Andrea Aime
@geowolf
Technical Lead
GeoSolutions S.A.S.
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