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

[Moritz Lennert]

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

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