[gdal-dev] Polygonizer / Lines

[Chaitanya kumar CH]

Alisson,

Can you provide a sample dataset that didn't work?


On Fri, Mar 15, 2013 at 6:20 PM, Alisson Barbosa <alisson.uece at gmail.com>wrote:

> Thank you Chaitanya,
>
> I had read the explanation of Peter Halls. But that was *raster
> polygonization*. I am currently working with another type: *polygonization
> of OGRLineStrings*.
>
> My question was because i was not able to polygonize using the mentioned
> method. I created an OGRMultiLineString or an OGRGeometryCollection and
> added geometries (many OGRLineStrings) by addGeometry or
> addGeometryDirectly methods. But the polygonization always returned null.
>
> I solved using this:
>
> OGRMultiLineString *mls = new OGRMultiLineString();
> OGRMultiLineString* pTemp = NULL;
> while(...) //iteration of lines
> {
>         //creation of line
>         pTemp = static_cast<OGRMultiLineString*>(mls->Union(line));
>         if (pTemp != NULL)
>         {
>             if( mls != NULL)
>             {
>                 if( mls->getNumGeometries() > 0)
>                     delete mls;
>             }
>             mls = pTemp;
>         }
> }
>
> Thanks,
>
>
> 2013/3/14 Chaitanya kumar CH <chaitanya.ch at gmail.com>
>
>> Alisson,
>>
>> You can refer to the method's documentation here:
>> http://www.gdal.org/ogr/classOGRGeometry.html#a674319670e735bf6d4049300096157ec
>>
>> The mechanism of this operation was already explained Peter Halls in this
>> mailing list[1]. GEOS does a good job identifying line strings touching at
>> end points and then combining them to make rings and then polygons.
>>
>> However, it's your job to ensure that all the line strings passed to the
>> method are part of a single polygon.
>>
>> [1]: http://lists.osgeo.org/pipermail/gdal-dev/2012-November/034793.html
>>
>>
>> On Thu, Mar 14, 2013 at 11:58 PM, Alisson Barbosa <alisson.uece at gmail.com
>> > wrote:
>>
>>> Can you explain a bit better?
>>>
>>>
>>> 2013/3/14 Chaitanya kumar CH <chaitanya.ch at gmail.com>
>>>
>>>> Allison,
>>>>
>>>> Check out OGRGeometry::Polygonize()
>>>>
>>>> The result depends on the type of intersections in your lines.
>>>>
>>>> --
>>>> Best regards,
>>>> Chaitanya Kumar CH
>>>> On 14 Mar 2013 21:53, "Alisson Barbosa" <alisson.uece at gmail.com> wrote:
>>>>
>>>>> Hi friends,
>>>>>
>>>>> I have a set of OGRLineStrings and an OGRLinearRing with many
>>>>> intersections. I would like to polygonize this set of lines. Can anybody
>>>>> help me?
>>>>>
>>>>> Best regards,
>>>>> --
>>>>> Alisson Barbosa
>>>>> Systems Analyst - FUNCEME
>>>>> M.Sc. in Computer Science - MACC
>>>>> Graduate in Computer Science  - UECE
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> gdal-dev mailing list
>>>>> gdal-dev at lists.osgeo.org
>>>>> http://lists.osgeo.org/mailman/listinfo/gdal-dev
>>>>>
>>>>
>>>
>>>
>>> --
>>> Alisson Barbosa
>>> Systems Analyst - FUNCEME
>>> M.Sc. in Computer Science - MACC
>>> Graduate in Computer Science  - UECE
>>>
>>>
>>
>>
>> --
>> Best regards,
>> Chaitanya kumar CH.
>>
>> +91-9494447584
>> 17.2416N 80.1426E
>>
>
>
>
> --
> Alisson Barbosa
> Systems Analyst - FUNCEME
> M.Sc. in Computer Science - MACC
> Graduate in Computer Science  - UECE
>
>


-- 
Best regards,
Chaitanya kumar CH.

+91-9494447584
17.2416N 80.1426E
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