[GRASS-dev] i.segment on panchromatic band of Worldview 2 scene: what resources are necessary to complete segmentation ?

[Yann Chemin]

1 - Find a faster CPU machine with 16Gb RAM and a SSD for a start, it
will be better,
Also if you have the opportunity check that the RAM is a 1800MHz one,
details like this may actually add your computation performance.


2 - Cut in pieces (See Markus Comment about supercomputing) and run 4
quads on 4 CPUs instead of one large image in one CPU.

3 - Recode i.segment to work natively on heterogeneous computers...
(would be fun!)

Good luck!

On 4 July 2013 14:10, Moritz Lennert <mlennert at club.worldonline.be> wrote:
> Hello,
>
> In parallel to the discussion going on in another thread, I have a question
> concering the segmentation of another Worldview 2 scene:
>
> I first used all 8 multispectral bands and managed to get a series of
> results with increasing thresholds in very reasonable running times. The
> region was as follows:
>
>> g.region -p
> projection: 1 (UTM)
> zone:       -36
> datum:      wgs84
> ellipsoid:  wgs84
> north:      7251172
> south:      7234772
> west:       333792
> east:       350192
> nsres:      2
> ewres:      2
> rows:       8200
> cols:       8200
> cells:      67240000
>
> and the command line:
>
> i.segment group=xs out=seg_xs minsize=2 memory=3072 threshold=0.05 (and
> thresh=0.1 and 0.2 in successive runs using the results of the previous run
> as seeds).
>
> Now, I would like to test segmentation of just the panchromatic band. This
> means the following region settings:
>
> projection: 1 (UTM)
> zone:       -36
> datum:      wgs84
> ellipsoid:  wgs84
> north:      7251172
> south:      7234772
> west:       333792
> east:       350192
> nsres:      0.5
> ewres:      0.5
> rows:       32800
> cols:       32800
> cells:      1075840000
>
> Trying to run with the following command line on my i3, 8GB RAM machine:
>
> i.segment group=pan out=seg_pan_005 threshold=0.05 memory=3072
>
> had the process running for almost 13 hours with it then becoming apparently
> stuck in the fourth pass at 10%. At that point the percent didn't change for
> over an hour, so I decided to kill the process. Can I assume that I'm here
> above the capacities of my machine ? Is there anything (besides working on a
> smaller subsample of the image) that I can do to make it work ? What kind of
> resources would I need to be able to run such a segmentation?
>
> I guess I'll have to move these kinds of treatments to our university
> supercomputer, but I first have to get them to install GRASS...
>
> Moritz
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