[GRASS-user] Help creating dissolved multipolygon

[Roger André]

Yes, and in fact the PostGIS geomunion function uses the "diss" field
just fine to group by.
--

On Tue, Oct 20, 2009 at 4:24 PM, M S <mseibel at gmail.com> wrote:
> If you query two adjacent polygons, do they both have the same value
> for the 'diss' attribute?
>
> On Tue, Oct 20, 2009 at 7:05 PM, Roger André <randre at gmail.com> wrote:
>> Yeah, kinda long, but here it is.  fwiw, I loaded the file into
>> PostGIS and let it crank away at the dissolve.  Was done after about
>> an hour, so while I'm thrilled to have the correct data, I'd still
>> like to figure out a solution in GRASS.
>>
>>> v.dissolve global_mask out=new_mask col=diss --o
>>  100%
>> Building topology for vector map <new_mask_18169>...
>> Registering primitives...
>> 5450 primitives registered
>> 288073 vertices registered
>> Building areas...
>>  100%
>> 2723 areas built
>> 2721 isles built
>> Attaching islands...
>>  100%
>> Attaching centroids...
>>  100%
>> Number of nodes: 5448
>> Number of primitives: 5450
>> Number of points: 0
>> Number of lines: 0
>> Number of boundaries: 2727
>> Number of centroids: 2723
>> Number of areas: 2723
>> Number of isles: 2721
>> v.reclass complete. 2723 features reclassed.
>> WARNING: Vector map <new_mask> already exists and will be overwritten
>> Extracting features...
>> Building topology for vector map <new_mask>...
>> Registering primitives...
>> 5450 primitives registered
>> 288073 vertices registered
>> Building areas...
>>  100%
>> 2723 areas built
>> 2721 isles built
>> Attaching islands...
>>  100%
>> Attaching centroids...
>>  100%
>> Number of nodes: 5448
>> Number of primitives: 5450
>> Number of points: 0
>> Number of lines: 0
>> Number of boundaries: 2727
>> Number of centroids: 2723
>> Number of areas: 2723
>> Number of isles: 2721
>> Writing attributes...
>> Removing duplicate centroids...
>> Building topology for vector map <new_mask>...
>> Registering primitives...
>> 5450 primitives registered
>> 288073 vertices registered
>> Building areas...
>>  100%
>> 2723 areas built
>> 2721 isles built
>> Attaching islands...
>>  100%
>> Attaching centroids...
>>  100%
>> Number of nodes: 5448
>> Number of primitives: 5450
>> Number of points: 0
>> Number of lines: 0
>> Number of boundaries: 2727
>> Number of centroids: 2723
>> Number of areas: 2723
>> Number of isles: 2721
>>
>>
>> On Tue, Oct 20, 2009 at 1:47 PM, MS <mseibel at gmail.com> wrote:
>>> Is there output for the dissolve command?
>>>
>>> Mark
>>>
>>> On Oct 20, 2009, at 4:37 PM, Roger André <randre at gmail.com> wrote:
>>>
>>>> Hi all,
>>>>
>>>> I'm having trouble creating a single, dissolved feature and exporting
>>>> it as a multipolygon.  Here is what I've done:
>>>>
>>>> - layer I started with:
>>>>>
>>>>> v.info -t global_mask
>>>>
>>>> nodes=5448
>>>> points=0
>>>> lines=0
>>>> boundaries=2727
>>>> centroids=2723
>>>> areas=2723
>>>> islands=2721
>>>> faces=0
>>>> kernels=0
>>>> primitives=5450
>>>> map3d=0
>>>>
>>>> - added dissolve field:
>>>>>
>>>>> v.db.addcol global_mask col="diss int"
>>>>> v.db.update global_mask col=diss value=1
>>>>
>>>> - check that diss field is there:
>>>>>
>>>>> v.info -c global_mask
>>>>
>>>> Displaying column types/names for database connection of layer 1:
>>>> INTEGER|cat
>>>> DOUBLE PRECISION|cat_
>>>> INTEGER|diss
>>>>
>>>> - dissolve:
>>>> v.dissolve global_mask out=new_mask col=diss --o
>>>>
>>>> - inspect new layer:
>>>>>
>>>>> v.info -t new_mask
>>>>
>>>> nodes=5448
>>>> points=0
>>>> lines=0
>>>> boundaries=2727
>>>> centroids=2723
>>>> areas=2723
>>>> islands=2721
>>>> faces=0
>>>> kernels=0
>>>> primitives=5450
>>>> map3d=0
>>>>
>>>> - export layer as shapefile:
>>>>>
>>>>> v.out.ogr -p input=new_mask type=area dsn=/tmp olayer=new_mask
>>>>
>>>> - check new shapefile:
>>>> ogrinfo -summary /tmp new_mask
>>>> INFO: Open of `/tmp'
>>>>     using driver `ESRI Shapefile' successful.
>>>>
>>>> Layer name: new_mask
>>>> Geometry: Polygon
>>>> Feature Count: 2723
>>>> Extent: (-180.000000, -90.000000) - (180.000000, 83.623596)
>>>> Layer SRS WKT:
>>>> GEOGCS["GCS_WGS_1984",
>>>>   DATUM["WGS_1984",
>>>>       SPHEROID["WGS_1984",6378137,298.257223563]],
>>>>   PRIMEM["Greenwich",0],
>>>>   UNIT["Degree",0.017453292519943295]]
>>>> cat: Real (11.0)
>>>>
>>>> As you can see, I still have 2723 features, when I expect to have 1.
>>>>
>>>> What am I doing wrong?
>>>>
>>>> Roger
>>>> _______________________________________________
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>>>> grass-user at lists.osgeo.org
>>>> http://lists.osgeo.org/mailman/listinfo/grass-user
>>>
>>
>