[GRASS-user] [GRASS-dev] Object-based image classification in GRASS

[Pierre Roudier]

Moritz,

Thanks heaps for the script. It's really is useful and will facilitate
the adoption of i.segment. It certainly would be a nice addition to
the wiki page.

Unfortunately I can't comment too much on this, as my object-based
classification projects are on hold, but I'll try to give that a shot
sometime soon.

It could also be interesting to try non-supervised approach using
i.segment to limit the "salt and pepper" noise affecting such
classifications.

Cheers,

Pierre



2013/10/31 Moritz Lennert <mlennert at club.worldonline.be>:
> Hello,
>
> Based on the great work on i.segment by Eric and MarkusM, I've been trying
> to put up a complete workflow allowing object-based image classification in
> GRASS. Conclusion: it is possible with currently available tools, even
> though some components would be nice to have in addition. Attached you can
> find a simple shell script which shows all the steps I went through. I
> commented it extensively, so it hopefully is easy to understand.
>
> Some remarks:
>
> - This only works in GRASS 7.
>
> - It uses the v.class.mlpy addon module for classification, so that needs to
> be installed. Kudos to Vaclav for that module ! It currently only uses the
> DLDA classifier. The mlpy library offers many more, and I think it should be
> quite easy to add them. Obviously, one could also simply export the
> attribute table of the segments and of the training areas to csv files and
> use R to do the classification.
>
> - At the top of the script are a series of parameters that have to be
> defined before being able to use the script as such (but the script is more
> meant as a proof-of-concept than as a real script)
>
> - Many other variables could be calculated for the segments: other texture
> variables (possibly variables by segment, not as average of pixel-based
> variables, cf [1]), other shape variables (cf the new work of MarkusM on
> center lines and skeletons of polygons in v.voronoi), band indices, etc. It
> would be interesting to hear what most people find useful.
>
> - I do the step of digitizing training areas in the wxGUI digitizer using
> the attribute editing tool and filling in the 'class' attribute for those
> polygons I find representative. As already mentioned in previous discussions
> [2], I do think that it would be nice if we could have an attribute editing
> form that is independent of the vector digitizer.
>
> More generally, it would be great to get feedback from interested people on
> this approach to object-based image classification to see what we can do to
> make it better.
>
>
> Moritz
>
> [1] https://trac.osgeo.org/grass/ticket/2111
> [2] http://lists.osgeo.org/pipermail/grass-dev/2013-February/062148.html
>
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