[SoC] SoC Report: GDAL TMS driver

Václav Klusák keo at keo.cz
Wed Jul 9 20:43:05 EDT 2008


Report for week 30.6.2008 -- 6.7.2008.

I finished a sketch of the driver. Compilable but not usable, XML parsing
was missing. I tried to come up with some way to enable the driver to
operate on huge datasets without sacrifising performance. I came up with a
solution involving several caching schemes, each tailored to different use
case (Dataset::RasterIO, RasterBand::RasterIO, RasterBand::ReadBlock). After
some deliberation it turned up it is of basicaly no use due to two reasons.

1) The way Dataset::RasterIO works. It just calls RasterIO on each raster
band in turn. The tiled dataset would be more efficient if the IO was
performed per block as in BlockBasedIO. This doesn't support Overviews
however.

2) This plan presumed that RasterBand blocks are 1:1 mappable to tiles on
disk, but actualy they are not. More on this in the next report.


Plan for the following week:

-- Learn how to use cpl_minxml.
-- Figure out different way to cache the tiles. Aggressive prefetching as I
intended before is probably out of question.

Václav "Keo" Klusák
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