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"
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.
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/w020n90.dem.zip/W020N90.DEM
or just :
gdalinfo
/vsizip/vsicurl/http://dds.cr.usgs.gov/srtm/version2_1/SRTM30/w020n90/w020n90.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/N00E006.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/w020n90.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.dem.
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
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