[Gdal-dev] A questions about IRasterIO and overlays

[James Gallagher]

I'm improving a GDAL driver for the DODS/OPeNDAP protocol. The driver
can read rasters from DODS/OPeNDAP servers. One problem with the current
implementation is that it always reads the entire raster. 

Before I dive into IRasterIO() I'd like to make sure providing my own
implementation of that method is really the best way to go. OPeNDAP
provides ways to read parts of rasters using the indexes combined with
an optional 'stride' value (which allows for sub-sampling).

I was also wondering about overlays and the comment that a driver that
provides its own implementation of IRasterIO() would normally implement
overlays. What exactly are 'overlays?'

As you can probably tell, I'm not that familiar with GIS software so my
apologies if these are really basic questions.

Thanks,
James
-- 
__________________________________________________________________________
James Gallagher		         The Distributed Oceanographic Data System
jgallagher at gso.uri.edu               http://unidata.ucar.edu/packages/dods
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