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I think I have a series of steps that will allow you to separate the
"inner" boundaries and generalize only those. The idea is based on
using the v.to.db module, with the "sides" option to add the cat
number of each area to the left and right of each boundary. Outer
boundaries will have "-1" (nothing on that side) for the left or
right sides. Then you can split out the inner boundaries with a
v.extract using a "where" clause.<br>
<br>
Somewhat convoluted, but here you are as regular grass command, not
in python.<br>
<br>
(My example below is from the sample nc_basic_spm_grass7 location. I
tested with the geology map.)<br>
<br>
<font size="+1"><tt># Make a copy and add cats to the boundaries in
layer 2</tt><tt><br>
</tt><tt>GRASS 7.4.0 (nc_basic_spm_grass7):~ > g.copy
vect=geology,my_geol</tt><tt><br>
</tt><tt>GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.category
my_geol layer=2 type=boundary option=add output=my_geol2</tt><tt><br>
</tt><tt><br>
# Add attribute columns for the left and right sides in layer 2,
and populate from the areas in *layer 1*</tt><tt><br>
</tt><tt>GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.db.addtable
my_geol2 layer=2 column="left integer,right integer"</tt><tt><br>
</tt><tt>GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.to.db my_geol2
layer=2 option=sides column=left,right query_layer=1</tt><tt><br>
</tt><tt><br>
# Now use the left and right cat value to separate the inner and
outer boundaries</tt><tt><br>
</tt><tt>GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.extract
my_geol2 layer=2 out=inner_bndry type=boundary
where="left<>-1 and right<>-1"</tt><tt><br>
</tt><tt>GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.extract
my_geol2 layer=2 out=outer_bndry type=boundary where="left=-1 or
right=-1"</tt><tt><br>
</tt><tt><br>
# Convert inner boundaries to lines for smoothing, and run
generalize</tt><tt><br>
</tt><tt>GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.type
input=inner_bndry out=inner_lines layer=2 from=boundary to=line</tt><tt><br>
</tt><tt>GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.generalize
inner_lines method=douglas output=inner_lines_smooth thresh=1000
--o</tt><tt><br>
</tt><tt><br>
# Convert back to boundary and merge back with the outer
boundary</tt><tt> and recreate area centroids<br>
</tt><tt>GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.type
inner_lines_smooth out=inner_bndry_smooth from=line to=boundary
layer=2 --o</tt><tt><br>
</tt><tt>GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.patch
input=outer_bndry,inner_bndry_smooth output=merge_smooth --o<br>
GRASS 7.4.0 (nc_basic_spm_grass7):~ > v.centroids
merge_smooth output=merged_areas layer=2 option=add<br>
<br>
</tt><tt></tt></font><br>
You probably will have to do some manual cleaning of the result,
since the smoothed inner boundaries might no longer exactly
intersect with the untouched outer boundary due to overshoots, etc.<br>
<br>
If you try this, let us know how it went.<br>
<br>
Regards, Micha<br>
<br>
<br>
<br>
<div class="moz-cite-prefix">On 08/24/2018 06:43 PM, Daniel
McInerney wrote:<br>
</div>
<blockquote type="cite"
cite="mid:58a9ee4f-31ba-b9a9-34a6-d2bf2534e71f@gmail.com">
<pre wrap="">Hi List,
I'm using v.generalize in a script (excerpt included below) to smooth
the boundaries of a polygon vector dataset. In the attached example
(input_vector.png), I would like to *only* generalize the internal lines
(blue), and leave the external boundary (green line) unchanged. I
thought that the flag, '-l' might provide this functionality, but
unfortunately the resulting external boundary is changed significantly
(attached vgeneralize_output.png).
Is this functionality available in v.generalize or is there another way
that this could be achieved in GRASS?
Thanks in advance.
Best regards,
Daniel.
##run generalisation (step: 1 - douglas)
gscript.run_command('v.generalize', flags='l', overwrite=True,
input='segments', output='segments_douglas', method='douglas', threshold=1)
##run generalisation (step: 2 - sliding average)
gscript.run_command('v.generalize', flags='l', overwrite=True,
input='segments_douglas', output='segments_douglas_slide',
method='sliding_averaging', threshold='2', look_ahead='9', slide='0.1',
iterations='3')
##run generalisation (step: 3 - snake)
gscript.run_command('v.generalize', flags='l', overwrite=True,
input='segments_douglas_slide', output='segments_douglas_slide_snake',
method='snake', threshold='3', alpha='1', beta='1')
</pre>
<br>
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<br>
<pre wrap="">_______________________________________________
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</blockquote>
<br>
<pre class="moz-signature" cols="72">--
Micha Silver
Ben Gurion Univ.
Sde Boker, Remote Sensing Lab
cell: +972-523-665918</pre>
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