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

[Moritz Lennert]

After some improvements to the module by MarkusM, I tried again during 
the night, but it got stuck again with heavy swapping going on. I'm 
definitively giving up to segment the panchromatic image in its entirety 
on my machine.

Question: Does the memory= parameter limit total memory usage of the 
module, or does it only limit the memory usage for certain parts of it ?

On 07/07/13 11:52, Yann Chemin wrote:
> 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.

I'll try on a machine with more RAM and better CPU (i7 instead of i3).

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

I can do that. Will this have any influence on segmentation results ?

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

Would parallization help ? Should i.segment be included into the list of 
OpenMP candidates:
http://grasswiki.osgeo.org/wiki/OpenMP#Candidates ?

Moritz

> 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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>
>
>