Le jeudi 24 mars 2011 19:03:57, Joaquim Luis a écrit : > Even, Chaitanya > > Thanks for hint. > > I did read the http://trac.osgeo.org/gdal/wiki/UserDocs/ReadInZip but it > hasn't any mention to the need of using "vsicurl"
Yes I am aware that it is lightly documented. I've added recently a few pointers though : - in the GDALOpen() doc : http://gdal.org/gdal_8h.html#e97be045eb4701183ad332ffce29745b which points to : http://gdal.org/cpl__vsi_8h.html#4f791960f2d86713d16e99e9c0c36258 Which mentions : "This special file handler can be combined with other virtual filesystems handlers, such as /vsizip. For example, /vsizip//vsicurl/path/to/remote/file.zip/path/inside/zip" Perhaps a more didactic page would be needed in the wiki. Any taker :-) ? I remind that the wiki is open in writing for everyone with an osgeo id... > > I was about to do the tests you did, so thank you also for that. > The point here is not to read that file in particular. I just wanted to > use one as example and one that is not a *.tar.gz that the docs say it > won't work. Ah... well actually reading in a .tar or a .tar.gz is now supported ( http://gdal.org/cpl__vsi_8h.html#d6dd983338849e7da4eaa88f6458ab64 ). Seems that I have changed my mind since. But seeking will still be very slow of course (especially if you combine with /vsicurl !). Ok, I'm going to rectify the page about that point. > Ok, I have enough information to make it possible to read some > compressed files sitting somewhere in the web and have the data land > directly in the internals of GMT. > > Thanks > > Joaquim > > > Joaquim, > > > > The correct syntax would be : > > > > gdalinfo > > /vsizip/vsicurl/http://dds.cr.usgs.gov/srtm/version2_1/SRTM30/w020n90/w02 > > 0n90.dem.zip/W020N90.DEM > > > > or just : > > > > gdalinfo > > /vsizip/vsicurl/http://dds.cr.usgs.gov/srtm/version2_1/SRTM30/w020n90/w02 > > 0n90.dem.zip > > > > because the zip file only contains one single file (W020N90.DEM) > > > > ... But the W020N90.DEM inside the zip file isn't directly recognized by > > GDAL (even if you download it and unzip the file). It's just a RAW file, > > that neads an header to tell the dimension, georeferencing, datatype > > etc, so the above won't directly work. > > > > You can for example create a VRT that refers to the raw file : > > > > <VRTDataset rasterXSize="4800" rasterYSize="6000"> > > > > <GeoTransform>-20, 8.3333333333300008e-03, 0, 90, 0, > > > > -8.3333333333300008e-03</GeoTransform> > > > > <VRTRasterBand dataType="Int16" band="1" subClass="VRTRawRasterBand"> > > > > <NoDataValue>-9999</NoDataValue> > > <SourceFilename > > > > relativetoVRT="0">/vsizip/vsicurl/http://dds.cr.usgs.gov/srtm/version2_1/ > > SRTM30/w020n90/w020n90.dem.zip</SourceFilename> > > > > <ByteOrder>MSB</ByteOrder> > > > > </VRTRasterBand> > > > > </VRTDataset> > > > > I've deduced this VRT from the > > http://dds.cr.usgs.gov/srtm/version2_1/SRTM30/w020n90/w020n90.hdr.zip > > file that sits next to the .dem.zip file. > > > > It's a shame that they didn't put the .hdr and the .dem file inside the > > same zip. It would have they been possible to open it directly... > > > > With the SRTM3 in HGT format, you can directly do : > > > > gdalinfo > > /vsizip/vsicurl/http://dds.cr.usgs.gov/srtm/version2_1/SRTM3/Africa/N00E0 > > 06.hgt.zip > > > > Best regards, > > > > Even > > > >> Hi, > >> > >> How do we access to a compressed files by URL? We can do that, can't we? > >> > >> As an example I try this (on Windows) > >> > >> gdalinfo > >> /vsizip/C:\http://dds.cr.usgs.gov/srtm/version2_1/SRTM30/w020n90/w020n90 > >> .de m.zip ERROR 4: > >> `/vsizip/C:\http://dds.cr.usgs.gov/srtm/version2_1/SRTM30/w020n90/w020n9 > >> 0.d em.zip' does not exist in the file system, > >> and is not recognised as a supported dataset name. > >> > >> and this > >> > >> gdalinfo > >> /vsizip//http://dds.cr.usgs.gov/srtm/version2_1/SRTM30/w020n90/w020n90.d > >> em. zip > >> > >> but the error message is similar. > >> > >> The idea is to fetch the data directly into GMT, but first I need to > >> understand well how it works. > >> > >> Thanks > >> > >> Joaquim Luis > >> _______________________________________________ > >> 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
