[GRASS-dev] Re: v.krige.py Documentation
a.ghisla at gmail.com
Wed Sep 2 08:05:10 EDT 2009
Il giorno mer, 02/09/2009 alle 07.30 -0400,
grass-dev-request at lists.osgeo.org ha scritto:
> I am attempting to use the v.krige.py extension with RC 5 by testing
> it with 20,000 points that it is trying to allocate 3 gigabytes of
> memory for and failing (which is odd because I have 8 GB on this
> machine and top reports that I have 4.3 GB free). I was able to
> successfully krig 5,000 points.
first of all thanks for testing v.krige. Your case study is very useful
for v.krige improvement.
> Ultimately I need to be able to handle around a million points - not
> looking like it will be possible based on my test.
> Can anyone tell me what the required memory is based on? Is it based
> on the region, the points, the block size, etc?
On the number of points and on the region. They both contribute to
create large intermediate and output objects.
R memory usage use deserves some consideration: you can find information
here [0,1]. I know it is a limitation when handling large datasets: a
good improvement for the code will be for example to store objects on
the hard drive instead of RAM. Alternatively, v.krige could work on a
slice of data at once, but I don't know if it is possible - worth to ask
to Roger Bivand and Edzer Pebesma.
> Also, I can find very little documentation for it. For instance I am
> not sure what the block size is used for, how is it different than the
> cell size set with g.region?
Block size is a parameter used by block kriging, different from region
resolution - see krige() documentation and examples .
> It looks very interesting if I were able to actually use it.
> The only documentation I can find for it is the man page and the wiki
> page neither of which really address any of these questions.
That's right - as v.krige is just a wrapper, its documentation should
contain all useful pointers to the code it includes. Will improve this
> Note that I can only run it from the command line, when I try to start
> the wxpython interface it displays a box for an instant and then quits
> without any error messages.
I suppose you run Windows: that's what happen when you use head revision
of v.krige and an outdated revision of GRASS. The module is presently
developed with develbranch_6, so needs recent updates (r38834 or
higher). I plan to improve backward compatibility in the near future.
Hope this helps!
> Jeshua Lacock, Owner
> phone: 208.462.4171
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