[gdal-dev] Reprojecting a tiled dataset

Frank Warmerdam warmerdam at pobox.com
Wed Nov 24 11:37:30 EST 2010

Mike Leahy wrote:
> To carry on the externally-tiled vs. internally-tiled discussion - another 
> question I have is what should I do about the large areas of empty space 
> around the outside of a non-rectangular dataset?  In the dataset I'm working 
> with at the moment, about 30% of the one-file image area is black/nodata.  This 
> can be excluded if I tile the dataset an remove any tiles with all zero 
> values.  Is there an equivalent way to exclude this within an internally-tiled 
> image in order to conserve disk space?  Would it have made a difference if I 
> had set the -srcnodata flag when I used gdalwarp?
> I must say, however, the performance of working with the internally tiled 
> image noticably better.  I gind I get significant loading/lag time when I view 
> the data using the *.vrt for the original tiled data within QuantumGIS, while 
> it's virtually instantaneous with with the single internally-tiled image.  So 
> if the cost for this is the extra disk space for the nodata regions, it's 
> worth it anyway.


My suggestion would be to use some sort of lossless compression scheme
if you have large nodata areas.  This will compress these tiles down to
almost nothing.  For instance adding "-co COMPRESS=DEFLATE".

GDAL can also support empty tiles in GeoTIFF but it isn't trivial to
utilize this capability in your situation.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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