[GRASS5] Re: v.clean rmsa option - what does it do ?

[Radim Blazek]

On 4/28/06, Moritz Lennert <mlennert at club.worldonline.be> wrote:
> Radim Blazek wrote:
> > On 4/27/06, Moritz Lennert <mlennert at club.worldonline.be> wrote:
> >
> >>Hello Radim,
> >>
> >>Could you (or someone else who knows this) give a more thorough
> >>explanation of what the 'rmsa' option of v.clean does (ideally in some
> >>graphical form) ?
> >>
> >>The man page says "remove small angles between lines at nodes", but I
> >>don't really understand what this means and the French translators of
> >>the manuals are trying to understand...
> >
> >
> > If angle between 2 lines is smaller than threshold the lines
> > are broken and the partialy merged.
>
> Thanks for the explanation.
>
> So if I understand correctly it does what is shown here:
>
> http://geog-pc40.ulb.ac.be/grass/rmsa.pdf

No, this can be don with 'prune' but tolerance is distance.

I have attached picture of what rmsa does.

Radim

> i.e. converting the black line with a small angle into the new red line.
>
> However, when I try to apply this to this line:
>
> http://geog-pc40.ulb.ac.be/grass/rmsa_example.jpg
>
> defined as follows in v.build:
>
>  > v.build brol
> Building topology ...
> 3 primitives registered
> Building areas:  100%
> 0 areas built
> 0 isles built
> Attaching islands:
> Attaching centroids:  100%
> Topology was built.
> Number of nodes     :   4
> Number of primitives:   3
> Number of points    :   0
> Number of lines     :   3
> Number of boundaries:   0
> Number of centroids :   0
> Number of areas     :   0
> Number of isles     :   0
>
>
>
> in the following projection:
>
>   > g.proj -p
> -PROJ_INFO-------------------------------------------------
> name       : Lambert Conformal Conic
> proj       : lcc
> datum      : bel72
> a          : 6378388
> es         : 0.0067226700
> lat_1      : 49.83333333333334
> lat_2      : 51.16666666666666
> lat_0      : 90
> lon_0      : 4.356939722222222
> x_0        : 150000.01256
> y_0        : 5400088.4378
> no_defs    : defined
> -PROJ_UNITS------------------------------------------------
> unit       : metre
> units      : metres
> meters     : 1
>
> Then whatever the threshhold value I set (going up to ridiculous values,
> I continue to get 4 nodes, with  3 lines which look identical to the
> original.
>
> Am I still wrong in my understanding of rmsa, or is it something else ?
>
> Moritz
>
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