[GRASS-user] i.maxlik's reject versus i.segment's goodness

[Markus Neteler]

On Sun, Nov 16, 2014 at 3:21 AM, Vaclav Petras <wenzeslaus at gmail.com> wrote:
> Hi,
>
> I executed the examples in i.cluster and i.maxlik manuals and also the
> following i.segment command:
>
> i.segment group=lsat7_2002 at w1-imagery output=lsat7_2002_segments
> threshold=0.5 goodness=lsat7_2002_segments_goodness
>
> (using the imagery group created in i.cluster example, otherwise unrelated)
>
> I looked at goodness from i.segment and then reject from i.maxlik. I noticed
> that there is some correlation between these two. Well, this is quite okay
> since they are using same pixel values. However, then I noticed that low
> values of goodness (-5000, ...) correlate with low values of reject (1 ==
> 1%). But the i.maxlik manual says that "1 = keep and 16 = reject". Can
> somebody explain this to me and perhaps suggest improvement to the manual?
> Shouldn't high rejection correlate with low goodness?

Unless someone looks at the source code, the i.maxlik manual may
simply be wrong.

A nice, synthetic test case would be the best.

> And also, less important thing, i.maxlik reject is an categorical map with
> percentages reclassified to 16 classes. Does this have some practical
> meaning or is this just an over-left from integer-only times?

Yes, that's likely and should be changed.

Markus

> Thanks,
> Vaclav
>
> http://grass.osgeo.org/grass71/manuals/i.cluster.html
> http://grass.osgeo.org/grass71/manuals/i.maxlik.html
> http://grass.osgeo.org/grass71/manuals/i.segment.html
>
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