[GRASS-user] patch boundaries

[Markus Metz]

On Fri, Jun 8, 2012 at 5:58 AM, Daniel Victoria
<daniel.victoria at gmail.com> wrote:
> Hi all,
>
> I'm having a hard time trying to get one boundary polygon file from
> four smaller shapes. I'm using wingrass7, daily build from today.
>
> This is how it goes. I have four boundaries which I imported and
> patched (v.patch).
> I then tried to dissolve the four separate boundaries into one but
> first, since the tiles do not match perfectly (they don't overlap), I
> tried v.clean with tools break polygons, snap boundaries and remove
> duplicate. Then, when I try to v.dissolve, nothing happens, I still
> end up with 4 polygons. Then I saw that I only had one item in the
> attribute table however, I have four polygons in the vector. I tried
> using v.to.db to add the missing polygons to the attribute table but I
> did not have any luck. I believe I'm missing something obvious which I
> just can't see. Any help is very much appreciated.

You can try to import all shapefiles at once (one shapefile is one OGR
layer and ends up as one GRASS layer):

v.in.ogr dsn=duke_analisys out=duke_analysis snap=1 min_area=100 --v

The snapping threshold comes from trial and error. In the imported
vector, the number of areas is equal to the number of centroids, 4,
thus there are no holes left inside or between polygons.

Have a look at the categories:
v.category in=duke_analysis out=duke_analysis_cat1 op=report

Add category 1 to layer 1 for each centroid (needed for dissolving):
v.category in=duke_analysis out=duke_analysis_cat1 layer=1 op=add
cat=1 step=0 type=centroid

Dissolve by categories:
v.dissolve input=duke_analysis_cat1 layer=1 output=duke_analysis_dissolved

One area left, done.

HTH,

Markus M

>
> Thanks
> Daniel
>
> PS - I attached the files because they are very small, just in case
> someone wants to take a look. They are in UTM 19S WGS84
>
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