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

[Markus Metz]

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
>>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/grass-user/attachments/20190619/a70a89ca/attachment.html>