[GRASS-dev] removing small multiple polygons created by r.stream.basin + r.to.vect

[Margherita Di Leo]

Hi,

when I delineate a basin using r.stream.basins, and convert the raster map
of the basin into vector (r.to.vect), I sometimes get multiple polygons:
i.e. one bigger and a couple of one cell polygons. (you can reproduce the
behavior in NC sample dataset using easting=643677.87 northing=222800.246).
Since i need to remove the small polygons in a script, I would like to know
whether I can use:

        grass.run_command('v.extract', list = 1,
                                       input = v_basins,
                                       output = v_basin,
                                       type = 'area',
                                       overwrite = True)

In fact, it seems to me that the bigger polygon is always listed as the
first record. Is that always true? Does r.to.vect (feature=area) always
list as first record the polygon with the larger area?
Or else, I should set a SQL query about the area. I've already tried
something like:

        grass.run_command('v.extract', where = 'area = max(area)',
                                       input = v_basins,
                                       output = v_basin,
                                       type = 'area',
                                       overwrite = True)

but it seems that the SQL statement is incorrect ... I'm not experienced
with SQL.
Any idea?

Thanks,
madi




-- 
Ing. Margherita Di Leo, Ph.D.
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