Hi,
While work is ongoing concerning improving r.to.vect performance [1], I
am looking at the possibility of creating an r.zonal.geometry module
which would calculate a series of form statistics for raster zones (aka
clumps). I would begin simply by trying to replicate the v.to.db
statistics, i.e. area and perimeter, with compactness and fractal
dimension derived from the two former.
Area calculation is quite simple (and already exists, for example, in
r.stats.zonal with the count method). However, perimeter is a bit more
complicated. My current idea is to 'simply' fetch raster info into a SEG
structure and to check for each pixel whether the upper, lower, left and
right neighbor has the same cat value as the current pixel. For each
neighbor where this is not the case, I add one pixel edge to the total
zonal perimeter.
Does this sound like the correct approach. Is there some already
existing code that I don't know about that already does this ?
Just trying to avoid reinventing the wheel.
My current motivation is to allow a complete OBIA toolchain without
going through vectorization at any point. At this stage, both
i.segment.stats and v.area.stats require the vectorization of raster
zones for shape statistics which makes the process very slow.
Moritz
[1] https://trac.osgeo.org/grass/ticket/2045
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