[GRASS-user] Grass 7.6 i.segment minsize working?

[Jamille Haarloo]

Thank you Markus!

I meant that I was literally seeing in the map display how the smallest
segments corresponded exactly with single (10 by 10) pixels of the input
data. I realize now, the module was using the pixel/cell units as
determined by the region settings. I overlooked this when starting the
project. Now I am better aware of how fundamental and how easy it is to
adjust/ reset the region settings. I changed the resolution to 10 and got
better results. According to r.stats the smallest segments have the minsize
of 10 I used this time!

Thanks a lot for your clear remarks and suggestions!

Best,
Jamille

On Wed, Jun 19, 2019 at 6:07 PM Markus Metz <markus.metz.giswork at gmail.com>
wrote:

> Hi Jamille,
>
> On Tue, Jun 18, 2019 at 10:40 PM Jamille Haarloo <j.r.haarloo at gmail.com>
> wrote:
> >
> > Thank you Markus,
> >
> > I used this data:
> https://drive.google.com/file/d/1xrLJY5aZLKE-ja51wKRX_CKKcUtIiy16/view?usp=sharing
> (excluding band 6. I used band 1-5 as group)
> >
> > The parameters:
> > i.segment.hierarchical group=S2bands_VV at LUPS thresholds=0.1, 0.2
> output=hier_segmS2 minsizes=20 memory=4000 iterations=30
> >
> > i.segment --overwrite group="S2bands_VV" output="SegmS2_02_20"
> band_suffix="Modified" threshold=0.2 radius=1.5 method="region_growing"
> similarity="euclidean" minsize=20 memory=4000 iterations=50 goodness=
> "goodn_of_fit_SegmS2_02_20"
> >
> > g.region -p
>
> > projection: 1 (UTM)
> > zone:       21
> > datum:      wgs84
> > ellipsoid:  wgs84
> > north:      620222.920747
> > south:      617573.079721
> > west:       782605.544297
> > east:       785903.817009
> > nsres:      0.49997
> > ewres:      0.49996555
> > rows:       5300
> > cols:       6597
> > cells:      34964100
>
> the region settings don't make sense because the resolution if the input
> data is 10 meter, not 0.49997 or 0.49996555. That means one original cell
> is converted to appr. 400 cells in the current region. If you really want
> to work with a resolution of appr. 0.5, you need to find a reasonable way
> to resample the 10 meter input data to 0.5 meter. I don't know a method to
> resample these input data to 0.5 meter resolution that is really enhancing
> the spatial detail not just multiplying existing spatial detail (more
> content, same amount of info).
>
> With these region settings, I get a minimum size of 120 cells for
> resultant segments according to "r.stats -c", with both
> i.segment.hierarchical and i.segment as used by you. Where do you see
> segments of just one pixel?
>
> Markus M
> >
> >
> > On Tue, Jun 18, 2019 at 5:04 PM Markus Metz <
> markus.metz.giswork at gmail.com> wrote:
> >>
> >>
> >>
> >> On Tue, Jun 18, 2019 at 3:31 PM Jamille Haarloo <j.r.haarloo at gmail.com>
> wrote:
> >> >
> >> > Dear Grass members,
> >> >
> >> > I have been testing i.segment and i.segment.hierarchical on a small
> region with Sentinel bands. However, the results consistently include
> segments of just one pixel even-though minimal segment sizes of 10 and 20
> were indicated. The final run with minsize 20 created 8247 segments.
> >> > There were no errors nor warnings, and I couldn't find the i.segment
> script to review it.
> >>
> >> It is here:
> >> https://github.com/OSGeo/grass/tree/releasebranch_7_6/imagery/i.segment
> >>
> >> > I also tried with a minsize of one (1). The result looks similar with
> even less segments created - a total of  8160.
> >> > I tried with Grass Gis 7.6.0 and 7.6.1(download of yesterday).
> >>
> >> I tested in the North Carolina sample dataset with
> >> g.region -p rast=lsat7_2002_10
> >>
> >> using default minsize 1
> >> i.segment group=lsat7_2002_10,lsat7_2002_20,lsat7_2002_30,lsat7_2002_40
> thresh=0.05 out=lsat7_2002_min1
> >> --> i.segment complete. Number of segments created: 29399
> >>
> >> r.info -r lsat7_2002_min1
> >> min=1
> >> max=29399    <-- as expected
> >>
> >> using minsize=20
> >> i.segment group=lsat7_2002_10,lsat7_2002_20,lsat7_2002_30,lsat7_2002_40
> thresh=0.05 out=lsat7_2002_min20 minsize=20
> >> --> i.segment complete. Number of segments created: 2114
> >>
> >> r.info -r lsat7_2002_min20
> >> min=1
> >> max=2114    <-- as expected
> >>
> >> r.stats -c lsat7_2002_min20 | sort -k 2n | head
> >> 1025 20
> >> 1081 20
> >> 109 20
> >> 1117 20
> >> 1220 20
> >> 1305 20
> >>
> >> The given minimum segment size is in this test respected.
> >>
> >> Can you provide test data, region settings and parameters for i.segment
> to reproduce?
> >>
> >> Markus M
> >>
>
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