[gdal-dev] Tiling aerial photos

Even Rouault even.rouault at mines-paris.org
Thu Jul 12 03:51:34 PDT 2012

Selon "Paul Meems (Top-X)" <p.meems at topx-group.nl>:

> Thanks Even,
> http://www.gdal.org/gdalbuildvrt.html does seems very interesting.
> As I understand it, it will do the merging part (without actually merging).

The VRT driver will do on-the-fly merging of tiles that have overlapping. The
VRT itself is just a XML file.

> But it doesn't do the tiling part, right?

No, I wasn't sure if your photos were already regularly tiled or not. Note that
the VRT accepts non regularly tiled images. They can have overlapping, gaps,
different resolutions, etc. The main constraints are :
- they are in the same projection
- they are "north-up", that is to say there is no rotation or skewing term in
their geotransform matrix
- they have the same number of bands

> Or is the vrt so optimized tiling
> is no longer necessary?

Not necessary. Note that the VRT has no internal spatial indexing, so if you
have several dozains of thousands of images in a VRT, it might slow down because
it will iterate over all the image descriptions (without needing to open them
however, all the information is in the VRT) to see if they intersect with the
request window. But I'd expect the number of images in the VRT to be really high
for that effect to become noticeable.

> Thanks,
> Paul

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