[gdal-dev] Polygonizer / Lines

[Alisson Barbosa]

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
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