[gdal-dev] The vrt datasource from gdalbuildvrt report a wrong block of 128x128

[Even Rouault]

Le dimanche 23 août 2015 14:18:03, Andrea Peri a écrit :
> Hi Even,
> 
> I just notice that in the page
> http://www.gdal.org/gdalinfo.html
> 
> In the sample reported is write a bloc size of 512x16:
> >Band 1 Block=512x16 Type=Byte, ColorInterp=Gray
> 
> Should it be a typo error ?

There's no typo. It is a TIFF with strip organization since the block width is 
the raster width.

There are various shapes of blocks :
- rectangular (typically square) blocks. e.g a tiled TIFF
- blocks whose width is the raster width. e.g. a stripped TIFF
- blocks whose height is the raster height. This is far less common, but 
occurs in some formats like DTED.

> 
> A.
> 
> 2015-08-23 11:40 GMT+02:00 Even Rouault <even.rouault at spatialys.com>:
> > Le dimanche 23 août 2015 11:28:21, Andrea Peri a écrit :
> >> Hi Even,
> >> thx for reply.
> >> 
> >> So actually a tiff born to be used with vrt datasource be better if
> >> you was with a tile=128x128 instead of tile=1024x1024
> >> 
> >>  right ?
> > 
> > I guess that should help in most cases, but almost due to the reduced
> > tile size than the matching between TIFF and VRT block size. For
> > example, if the VRT is read by an algorithm that processes line by line,
> > a reduced tile size will cause less data to be read.
> > Increasing GDAL_CACHEMAX can also be an alternative
> > 
> >> A.
> >> 
> >> 2015-08-23 10:51 GMT+02:00 Even Rouault <even.rouault at spatialys.com>:
> >> > Le dimanche 23 août 2015 07:43:03, Andrea Peri a écrit :
> >> >> Hi,
> >> >> I have a tiff tiled with tile size 1024 x 1024.
> >> >> 
> >> >> When I try to build a vrt-datasource on it using the gdalbuildvrt.
> >> >> I see the result vrt file report a
> >> >> block of 128x128 instead of 1024x1024.
> >> >> 
> >> >> I dont know if this is correct by the gdalbuildvrt oint of view
> >> >> 
> >> >> Also I like to know if is preferrably to correct manually  the vrt
> >> >> result to report the right value 1024
> >> >> or is also acceptable to maintain the 128 size reported for the right
> >> >> work of the gdal utilities in the vrt file.
> >> > 
> >> > Andrea,
> >> > 
> >> > the 128x128 block size is currently hardcoded in the VRT driver. We
> >> > could imagine extending the VRT syntax to have user defined block
> >> > size.
> >> > 
> >> > Even
> >> > 
> >> > --
> >> > Spatialys - Geospatial professional services
> >> > http://www.spatialys.com
> > 
> > --
> > Spatialys - Geospatial professional services
> > http://www.spatialys.com

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