On Mon, Jan 30, 2012 at 1:17 PM, John Twilley <math...@gmail.com> wrote: > I'm using gdalbuildvrt as a simple way to merge adjoining data files. > Unfortunately, I'm noticing that some values change. I've created a > simple test case where I make a VRT from a single GeoTIFF and compare > histograms before and after, and I've attached it to this message. > Can someone tell me why this is happening and how to avoid it? > Thanks!
John, It looks like your source TIFF file was generated by gdal_translate on an HDF file (or perhaps it has an .aux or .aux.xml file associated with it) and thus it has "built in" knowledge of the histogram which is getting used whether it reflects the reality of the image or not. This sort of histogram and statistics metadata is not copied to the VRT by gdalcreatevrt so a request for it ends up in recomputing from the imagery data. I'd assume then that the information from the destination file are right, and the source is wrong though it is hard to confirm this without having the imagery at hand to test. Best regards, -- ---------------------------------------+-------------------------------------- I set the clouds in motion - turn up | Frank Warmerdam, warmer...@pobox.com light and sound - activate the windows | http://pobox.com/~warmerdam and watch the world go round - Rush | Geospatial Software Developer _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev
