[gdal-dev] accessing zip files by URL

[Smith, Michael D ERDC-CRREL-NH]

Joaquim,

For .tar.gz, you can use /vsitar

Mike


-- 
Michael Smith
Remote Sensing/GIS Center
US Army Corps of Engineers
Hanover, NH



On 3/24/11  2:03 PM, "Joaquim Luis" <jluis at ualg.pt> wrote:

> 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/SRTM
>> 30/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.h
>> gt.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
>>> _______________________________________________
>>> gdal-dev mailing list
>>> gdal-dev at lists.osgeo.org
>>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>> 
> 
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