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<[email protected]> 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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