Ciao Jody, please see below... ------------------------------------------------------- Ing. Simone Giannecchini GeoSolutions S.A.S. Owner - Software Engineer Via Carignoni 51 55041 Camaiore (LU) Italy
phone: +39 0584983027 fax: +39 0584983027 mob: +39 333 8128928 http://www.geo-solutions.it http://simboss.blogspot.com/ http://www.linkedin.com/in/simonegiannecchini ------------------------------------------------------- On Fri, Apr 10, 2009 at 11:17 AM, Jody Garnett <[email protected]> wrote: > 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? Correct, but I am carrying around this info using a GridGeometry2D hence I have the all 3 anyway :-). > >> 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? y > >> - 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. > I am not sure I have fully understood your suggestions, however, to clarify, what I am looking for area ideas about how to compute the scale factor(s?) of a request for WMS/WCS in a generic way that can be portable between different CRS. So that I can use it to select overviews. Feedback on how people would expect us to select overviews are welcome as well. Simone. > 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 > _______________________________________________ > Geotools-devel mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/geotools-devel > ------------------------------------------------------------------------------ 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
