Le lundi 14 novembre 2011 18:23:23, Joaquim Luis a écrit : > Hi, > > I made a nice little tool for Mirone where one can very easily mosaic > either several flavors of SRTM grids or satellite images from Bing servers. > My question is about the SRTM30 grids (30 arc minutes) that are > available here (SRTM plus) > ftp://topex.ucsd.edu/pub/srtm30_plus/srtm30/data/ > which I would like to be able to access directly with the vsicurl > mechanism. The trouble in this case is that those grids are raw files > without any header file. When we have them on disk the simple solution > is to create a esri .hdr header from the information extracted from the > file name. However, this logic does not work for files seating in the > Web because the file and the header won't be located next to each other. > The same occurs if one has those files compressed. In this case the > header file cannot be assumed to be stored inside the .zip file and the > vsizip mechanism will fail for exactly the same reason. > My question is than, if there is a mechanism to send the header info to > the GDAL library and thus pretend that file and header leave side by > side? Note that I want to do this programmatically so need for an > already existing ready to use solution.
One way to do this is to use the capability of VRT files to describe raw files ( http://www.gdal.org/gdal_vrttut.html ), that offer similar capabilities than the EHdr header. For e020n40.Bathymetry.srtm, a quick test shows that the following should do : <VRTDataset rasterXSize="4800" rasterYSize="6000"> <SRS>GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]]</SRS> <GeoTransform>20, 0.008333333333333, 0.0, 40, 0.0, -0.008333333333333</GeoTransform> <VRTRasterBand dataType="Int16" band="1" subClass="VRTRawRasterBand"> <SourceFilename relativetoVRT="0">/vsicurl/ftp://topex.ucsd.edu/pub/srtm30_plus/srtm30/data/e020n40.Bathymetry.srtm</SourceFilename> <ImageOffset>0</ImageOffset> <PixelOffset>2</PixelOffset> <LineOffset>9600</LineOffset> <ByteOrder>MSB</ByteOrder> </VRTRasterBand> </VRTDataset> (I've attached it to avoid line wrapping problems) > > Thanks > > Joaquim > _______________________________________________ > gdal-dev mailing list > gdal-dev@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/gdal-dev
<VRTDataset rasterXSize="4800" rasterYSize="6000"> <SRS>GEOGCS["WGS 84",DATUM["WGS_1984",SPHEROID["WGS 84",6378137,298.257223563,AUTHORITY["EPSG","7030"]],AUTHORITY["EPSG","6326"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4326"]]</SRS> <GeoTransform>20, 0.008333333333333, 0.0, 40, 0.0, -0.008333333333333</GeoTransform> <VRTRasterBand dataType="Int16" band="1" subClass="VRTRawRasterBand"> <SourceFilename relativetoVRT="0">/vsicurl/ftp://topex.ucsd.edu/pub/srtm30_plus/srtm30/data/e020n40.Bathymetry.srtm</SourceFilename> <ImageOffset>0</ImageOffset> <PixelOffset>2</PixelOffset> <LineOffset>9600</LineOffset> <ByteOrder>MSB</ByteOrder> </VRTRasterBand> </VRTDataset>
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