you can use gdalinfo to check the structure of the data and gdal_translate/gdalado to modify them easily.
Simone. ------------------------------------------------------- Ing. Simone Giannecchini GeoSolutions S.A.S. Founder - 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://geo-solutions.blogspot.com/ http://www.linkedin.com/in/simonegiannecchini http://twitter.com/simogeo ------------------------------------------------------- On Wed, May 5, 2010 at 10:24 AM, Martin Tomko <[email protected]> wrote: > Aha, cool, I was not aware of that. > I am using SRTM DEM data, so subsampling is not an option, I need full res. > I should check if they are inner tiled (although I don't assume so). Is > that something that gdal can help me with, to perform the tiling? Any > hint welcome. > > Thanks for bearing with me! > M. > > > On 5/5/2010 10:16 AM, Andrea Aime wrote: >> Martin Tomko ha scritto: >>> Thanks Andrea, >>> I really don't know enough how the mechanisms work behind the scenes, >>> hence my question. >>> I understand that if you have a tiled source of coverage, only the >>> relevant tiles can be read. (btw, I only played with tiled tiffs a >>> long time ago - would have been 2.4 or so, and had troubles. Is there >>> a nice snipped of code available somewhere, showing how to start with >>> the GeoTIFF reader and an index shapefile?) >> >> You're talking about mosaics there. TIFFs can be inner tiled. >> >>> But is it really so that there is no way to read in only the >>> appropriate portion? >>> Imagine a tiff+world fiel, or a geotiff - IFF we could read just the >>> "metadata", we can reconstruct the Envelope (in the latter case even >>> referenced envelope), and do an intersect operation with any other >>> envelope, for instance coming from a geometry. The result of the >>> intersection could then be transformed into the grid coordinates of >>> the coverage (knowing the dimensions and the starting pixel), and >>> only read these in, with the new envelope set. >> >> No, it's not possible. Coverages are read by blocks. >> A PNG/JPEG is laid out so that you have to uncompress the whole to >> read, so it's not possible to do any cropping while reading. >> A inner tiled TIFF instead is structured so that the file is split into >> smaller blocks, and you read those instead (but each tile, you read >> fullh). >> If it's not tiled it's usually striped, so you can read one row at a >> time (and afaik, the row is the minimum unit that we can read). >> That said, assuming it's not compressed, if it is, it's just like >> a PNG/JPEG. >> >> When tiles/stripes are not compressed in theory it should be possible >> to read only parts of it, not sure what happens in that case (e.g., >> I know we can set subsampling, which will read one pixel out of >> every n as a cheap way to reduce the resolution, but not sure >> what happens about the ROI when reading). >> >> Cheers >> Andrea >> >> > > > ------------------------------------------------------------------------------ > _______________________________________________ > Geotools-gt2-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/geotools-gt2-users > ------------------------------------------------------------------------------ _______________________________________________ Geotools-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/geotools-devel
