Dear All, I have been discussing a little with aaime and daniele these days about better ways to pick overviews in gridcoverage upon a read request.
The assumption is that I am provided with the following: - bbox + crs - grid-to-world transform - image range (minx,miny,w,h) and I needed to do all the needed magic like, crop, select overview, decimate, resample, etc... Now, we have roughly identified 3 situations: 1> the coverage native CRS and the request crs are similar, i.e. no reprojection is needed between them 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 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). Case 1 can be handled with no problems relying on the gridtoworld transform of the request. For 2 and 3 i would like to hear opinions from other people about how to select the best overviews taking into account reprojection between the two spaces. My thoughts are: - 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 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). Ciao, Simone. ------------------------------------------------------- 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 ------------------------------------------------------- ------------------------------------------------------------------------------ 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
