[GRASS-user] Converting raster to polygon creates too many polygons

[razmjooeis at faunalia.co.uk]

You might consider using -s flag to smooth the corners.
Otherwise, I can't see why it doesn't work.

R.
Sab

> Hi,
>
> I've created subcatchments using r.watershed and I would like to
> convert these to polygons. My result at the moment contains too many
> polygons - 194. The original raster had only 9 areas, which should all
> have been contiguous seeing that they came from r.watershed.
>
> Here is the sequence of commands that I use, starting with r.report
> for the information about the subcatchments raster:
> -----
>  |   Type of Map:  raster               Number of Categories: 18
>  |   Data Type:    CELL
>  |   Rows:         33443
>  |   Columns:      33008
>  |   Total Cells:  1103886544
>  |        Projection: Transverse Mercator
>  |            N: -3122229.69982072    S: -3155672.30728643   Res:
> 0.99998826
>  |            E: -33474.90929218    W: -66483.27873573   Res: 1.00001119
>  |   Range of data:    min = 2  max = 18
> -----
>
> # Set the resolution to 25m
> g.region rast=c83a_border res=25
>
> # Convert the subcatchment raster to vector
> r.to.vect --overwrite
> input=c83a_dem_25m_clipped_basins_100000_clipped at PERMANENT
> output=c83a_subcatchments at PERMANENT feature=area
>
> v.report for the resulting vector gives me 194 categories. The
> original raster had only 9 areas, which should all have been
> contiguous seeing that they come from r.watershed.
>
> What am I doing wrong? I want an output vector with 9 polygons
> corresponding to the original 9 areas in the subcatchment raster.
>
> Thanks
> Hanlie
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