Hi Simone: > The assumption is that I am provided with the following: > - bbox + crs > - grid-to-world transform > - image range (minx,miny,w,h)
I do not follow why are all three are here; it appears to me that you could determine the image range based on the grid-to-world transform and the bbox+crs? > 2> the coverage native CRS and the request crs are NOT similar, i.e. a > reprojection is needed between them, and the requested envelope can be > reprojected to the coverage native CRS Okay. > 3> the coverage native CRS and the request crs are similar, i.e. a > reprojection is needed between them, and the requested envelope can > NOT be reprojected to the coverage native CRS (this usually happens > when going from project to geo or the other way around). Is this where one of the "edges" of the reprojected request envelope falls outside of the image; or outside of the valid area of the coordinate reference system? > - In the past, especially for 2 I was reprojecting the requested > envelope to the coverage CRS for computing the needed stuff for doing > a read. However this implies doing an implicit reprojection on the > requested grid geometry imposing that the raster range stay unchanged. > Therefore this may lead to a degradation of the resolution for the > request and to the selection of an overviews at a resolution lower > than needed. This is not good since in the end we need to reproject > again, therefore we might have raster data at a quality lower than > expected. I am imagining the target grid transformed into the image crs; forming lots of little trapezoid(or stranger) shapes. I think you could account for this with a little bit of math; taking the shortest horizontal distance / vertical distance produced by the transformed grid; and using that to select out the appropriate level of details. > - I am pretty sure we can merge 2 and 3 into a single case > - which assumption you'd expect for overviews? Many software have > great limitation (constant aspect ratio, constant scale factor==2, > etc..) and so do many important formats (jpeg2000 to mention one). I would expect to choose the overview that prevents the same source pixel being sampled twice for display. Jody ------------------------------------------------------------------------------ This SF.net email is sponsored by: High Quality Requirements in a Collaborative Environment. Download a free trial of Rational Requirements Composer Now! http://p.sf.net/sfu/www-ibm-com _______________________________________________ Geoserver-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geoserver-devel
