[gdal-dev] Reprojecting a tiled dataset
mgleahy at alumni.uwaterloo.ca
Wed Nov 24 11:27:32 EST 2010
On Tuesday, November 23, 2010 23:54:34 Frank Warmerdam wrote:
> Mike Leahy wrote:
> > On another note...if the output image is internally tiled, is it still
> > worthwhile to run gdaladdo on it? Is it generally about the same
> > efficiency to use the single internally-tiled file if I'm going to use
> > it as a layer in MapServer, or should I re-tile it again into separate
> > images?
> Absolutely you should build overviews for it. I don't see any value in
> turning it into a bunch of files - I much prefer serving from one, or only
> a few large GeoTIFF files instead of all this tiles-as-files business.
> Best regards,
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.
P.S.: I forgot to copy the list on my previous reply - sorry about that.
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