[GRASS-dev] Re: v.krige.py Documentation

[Dylan Beaudette]

2009/9/2 Anne Ghisla <a.ghisla at gmail.com>:
> Il giorno mer, 02/09/2009 alle 07.30 -0400,
> grass-dev-request at lists.osgeo.org ha scritto:
>> Greetings,
>>
>> 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.
>
> Hello Jeshua,
>
> 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.

Hi,

Note that with large point counts, and possibly high point density,
local smoothing approaches are probably more efficient. Check out RST
interpolation in GRASS for cases of >1 million points. I am pretty
sure that it scales efficiently to >50 million points.

Cheers,
Dylan

>> 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 [2].
>
>> 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
> asap.
>
>> 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!
>
> best regards,
> Anne Ghisla
>
>> Thanks,
>>
>> Jeshua Lacock, Owner
>> <http://OpenOSX.com>
>> phone: 208.462.4171
>
> [0]
> http://stat.ethz.ch/R-manual/R-patched/library/base/html/Memory-limits.html
> [1] http://www.matthewckeller.com/html/memory.html
> [2] http://sekhon.berkeley.edu/library/gstat/html/krige.html
>
>
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