[gdal-dev] vsigzip woes with hgt.gz files

[Vincent Schut]

On 08/23/2017 04:20 PM, Even Rouault wrote:
>
> On mercredi 23 août 2017 16:01:05 CEST Vincent Schut wrote:
>
> > Hi all,
>
> >
>
> > I'm trying to get the /vsigzip/ driver working on srtm .hgt.gz files,
>
> > but I don't succeed:
>
> >
>
> > gdalinfo /vsigzip/N37W105.hgt.gz
>
> > ERROR 4: `/vsigzip/N37W105.hgt.gz' not recognized as a supported file
>
> > format.
>
> > gdalinfo failed - unable to open '/vsigzip/N37W105.hgt.gz'.
>
> >
>
> > This is with a .hgt.gz from here:
>
> > https://s3.amazonaws.com/elevation-tiles-prod/skadi/N37/N37W105.hgt.gz
>
> >
>
> > gunzipping the file works OK.
>
> >
>
> > Any hints?
>
> Fixed per https://trac.osgeo.org/gdal/ticket/7016
>

Thanks Even!

> However opening time is really slow (which might be a problem or not 
> depending on what you're doing) as the whole file needs to be 
> downloaded and decompressed. The reason is that .hgt files are pure 
> raw data files without any header, so the only way to know the 
> dimensions is to check the file size against 3601*3601*2 bytes (SRTM 3 
> at low latitudes), 3601*1801*2 (SRTM 3 at high latitudes) or 
> 1801*1801*2 (SRTM 1). But for a .gz file, the only way to get the 
> uncompressed file size is to uncompress it...
>
> Even
>
> -- 
>
> Spatialys - Geospatial professional services
>
> http://www.spatialys.com
>

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