[GRASS-dev] i.gensiget: "Unreliable clustering. Try a smaller initial number of clusters"

[Blumentrath, Stefan]

Hi Nikos

I had similar problems with this module. My experience with i.gensigset is, that it can be quite sensitive for how training areas aredistributed and how well they can be distinguished.
I do not know the algorithm nor what exactly the problem was in my case. But I solved this error message by adjusting the training areas in a way that I added training areas for classes where I had a relatively lower number of pixels (compared to the number of pixels in other classes) in a first try and removed/reshaped possibly conflicting training units in order to avoid overapp in subsignatures across classes.
I do not know how you generated your training areas, but maybe you have a chance to try adjusting them...

Hope that helps and I am interested in what does the trick for you or what other, more experienced, users say on that topic...

Cheers
Stefan
________________________________________
Von: grass-dev-bounces at lists.osgeo.org [grass-dev-bounces at lists.osgeo.org]" im Auftrag von "Nikos Alexandris [nik at nikosalexandris.net]
Gesendet: Freitag, 28. Juni 2013 16:40
An: GRASS developers list
Betreff: [GRASS-dev] i.gensiget: "Unreliable clustering. Try a smaller  initial number of clusters"

Hi!

Today using i.gensigset, I bombed into this strange behaviour as the one
discussed in the past

<http://lists.osgeo.org/pipermail/grass-user/2010-April/055639.html>

where the module did not generate any signatures.  Anyone that knows what's
going on?  I have tried various stuff without success.

I also tried in the "imagery60/user1" location/mapset using the Spot subsets
(spot.ms.1, spot.ms2, spot.ms.3), and it just works fine!

Thanks, N
---


A test-case:

# where am I
g.proj -p

-PROJ_INFO-------------------------------------------------
name       : Universal Transverse Mercator
proj       : utm
datum      : wgs84
ellps      : wgs84
zone       : 48
no_defs    : defined
-PROJ_UNITS------------------------------------------------
unit       : metre
units      : metres
meters     : 1

# region
g.region -p

projection: 1 (UTM)
zone:       48
datum:      wgs84
ellipsoid:  wgs84
north:      178800
south:      137200
west:       163500
east:       225200
nsres:      100
ewres:      100
rows:       416
cols:       617
cells:      256672

# Top of Canopy Reflectance (from a Landsat 7 scene)
for Band in `g.mlist type=rast pat=ToCR?`; do r.info -r ${Band}; done

raster map(s) available in mapset <classification_trials>:
min=0.00124375210840126
max=0.35849866608563
min=0
max=0.35782345515399
min=0
max=0.379788238688478
min=0.00243176894430602
max=0.467877978869486
min=0.00498972477821269
max=0.405811742521198
min=263.377037572447
max=301.084746200043
min=0.00636355695948437
max=0.457282493983423

# a random samples map lies inside
r.info -gr random_trainingmap

north=178800
south=137200
east=225200
west=163500
nsres=100
ewres=100
rows=416
cols=617
cells=256672
datatype=CELL
min=1
max=5

# and is not empty
r.stats -cp random_trainingmap
 100%

1 155   0.06%
2 203   0.08%
3 90   0.04%
4 45   0.02%
5 104   0.04%
* 256075  99.77%

# grouping ToCRs
i.group group=spectral subgroup=123457
input=ToCR1,ToCR2,ToCR3,ToCR4,ToCR5,ToCR7

[..]

# attempting to generate signatures
i.gensigset trainingmap=random_trainingmap group=spectral subgroup=123457
signaturefile=123457

Finding training classes...
 100%
5 classes found
Reading raster maps...
 100%
Clustering class 1 (155 pixels)...
WARNING: Removed a singular subsignature number 1 (4 remain)
WARNING: Removed a singular subsignature number 1 (3 remain)
WARNING: Removed a singular subsignature number 1 (2 remain)
WARNING: Removed a singular subsignature number 1 (1 remain)
WARNING: Unreliable clustering. Try a smaller initial number of clusters
WARNING: Removed a singular subsignature number 1 (-1 remain)
WARNING: Unreliable clustering. Try a smaller initial number of clusters
Number of subclasses is 0
Clustering class 2 (203 pixels)...
WARNING: Removed a singular subsignature number 1 (4 remain)
WARNING: Removed a singular subsignature number 1 (3 remain)
WARNING: Removed a singular subsignature number 1 (2 remain)
WARNING: Removed a singular subsignature number 1 (1 remain)
WARNING: Unreliable clustering. Try a smaller initial number of clusters
WARNING: Removed a singular subsignature number 1 (-1 remain)
WARNING: Unreliable clustering. Try a smaller initial number of clusters
Number of subclasses is 0
Clustering class 3 (90 pixels)...
WARNING: Removed a singular subsignature number 1 (4 remain)
WARNING: Removed a singular subsignature number 1 (3 remain)
WARNING: Removed a singular subsignature number 1 (2 remain)
WARNING: Removed a singular subsignature number 1 (1 remain)
WARNING: Unreliable clustering. Try a smaller initial number of clusters
WARNING: Removed a singular subsignature number 1 (-1 remain)
WARNING: Unreliable clustering. Try a smaller initial number of clusters
Number of subclasses is 0
Clustering class 4 (45 pixels)...
WARNING: Too many subclasses for class index 4
Number of subclasses set to 4
WARNING: Removed a singular subsignature number 1 (3 remain)
WARNING: Removed a singular subsignature number 1 (2 remain)
WARNING: Removed a singular subsignature number 1 (1 remain)
WARNING: Unreliable clustering. Try a smaller initial number of clusters
WARNING: Removed a singular subsignature number 1 (-1 remain)
WARNING: Unreliable clustering. Try a smaller initial number of clusters
Number of subclasses is 0
Clustering class 5 (104 pixels)...
WARNING: Removed a singular subsignature number 1 (4 remain)
WARNING: Removed a singular subsignature number 1 (3 remain)
WARNING: Removed a singular subsignature number 1 (2 remain)
WARNING: Removed a singular subsignature number 1 (1 remain)
WARNING: Unreliable clustering. Try a smaller initial number of clusters
WARNING: Removed a singular subsignature number 1 (-1 remain)
WARNING: Unreliable clustering. Try a smaller initial number of clusters
Number of subclasses is 0
i.gensigset complete.
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