Le jeudi 15 décembre 2011 18:08:26, mlade...@distributel.net a écrit : > Hi all, > > I am trying to use gdal_translate to convert a .grd file > (Northwood/VerticalMapper format) to TIFF. However, the colors in the > translated file don't seem to be interpolated correctly based on the > color scheme, for values near the end of the range. > > Here is a link to the original GRD, as well as the exported TIFFs > (small download, only 200K): > http://dl.dropbox.com/u/53500018/GdalQuestion.zip > > The GdalTranslateExport.tif file was produced with the command > "gdal_translate -b 1 -b 2 -b 3 > C:\source\Ottawa_east_DEM30m_trim_copy.grd > C:\temp\GdalTranslateExport.tif". > > Notice the top and bottom areas of the image: they are yellow. For > comparison, take a look at the NativeExport.tif file in the same > package. The top and bottom areas are orange, as they should be. The > NativeExport.tif file was produced by Pitney Bowes MapInfo. > > Here is the color scheme for the GRD: > http://www.smugmug.com/photos/i-bRZ879w/0/X3/i-bRZ879w-X3.jpg > > Notice that the thresholds are "70" for yellow, and "161" for orange. > Well, the values at the top and bottom are in the high 130s/low 140s. > So they should be interpolated close to orange, not yellow. Therefore > the NativeExport.tif is correct, and the gdal_translate export is > incorrect. > > I have also tried changing the thresholds, and as soon as I change the > orange threshold to be below the maximum actual value in the GRD > (let's say 144), the gdal_translate export shows the orange shades.
Good analysis. There was indeed a bug in the way the end of the color palette is interpolated if the maximum z value is below a threshold of the color scheme. See http://trac.osgeo.org/gdal/ticket/4395 for the fix (a simple typo) > > So, it seems there might be a bug in gdal_translate where color values > are not interpolated correctly for thresholds that fall outside of the > range of actual values? Or is there a way to make gdal_translate > behave the way that I want with some different command line options? > > Regards, > Mladen Gavrilovic > > P.S. For convenience, here is a gallery with the TIFFs converted to > JPEG (difference is still obvious), and the color scheme: > http://smu.gs/vMEemF > > P.P.S Version of GDAL is 1.8.1 > > ---------------------------------------------------------------- > This message was sent using Distributel Webmail. > Ce message a été envoyé à partir de la Messagerie Web Distributel. > > > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/gdal-dev _______________________________________________ gdal-dev mailing list gdal-dev@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/gdal-dev