[gdal-dev] VRT derived band pixel functions written in Python

Rutger kassies at gmail.com
Tue Sep 13 02:07:39 PDT 2016

I overlooked the fact that it still moves through Python, is that the 'only'
hurdle preventing parallel IO? Since gdalwarp for example has the -multi
flag, it seems as if GDAL is capable of it, or is that a
specific/specialized implementation?

Numba has several options which might eliminate using Python during
execution. There are c-callbacks:

It probably works by using the Numpy C-API (which i have zero experience
with). I don't know if its possible that other programs, like GDAL, can also
use those compiled functions without moving to Python first.

There is also ahead-of-time compilation (AOT):

AOT has the benefit that users only need Numpy as a dependency, and don't
need Numba/llvm. There some drawbacks as well, like no longer being able to
compile optimizations for the hardware its running on.


Even Rouault-2 wrote
> Le mardi 13 septembre 2016 09:02:09, Rutger a écrit :
> I've only scratched up the surface of Numba (didn't know it 2 days ago). I 
> guess this might work (might only be interested if the 
> VRTDerivedRasterBand::IRasterIO() is called with a big enough region.
> Which 
> depends on the pixel access pattern of upper layers). The VRT drivers just 
> calls a Python function that takes numpy arrays and a few extra args.
>> And would that give parallel
>> processing for both IO and calculations?
> Only calculations. I/O is done before going to Python and after returning
> from 
> it.
> Actually... if you specify zero source in the VRT, then it is up to you to
> do 
> the read operations the way you like in Python, so you could possibly 
> parallelize them there.
> Even
> -- 
> Spatialys - Geospatial professional services
> http://www.spatialys.com
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