[vtkusers] Example of PointInPolygon

[Jothy]

Are you using vertex points instead of points inside the polygon. I mean, in
case of a sphere, are using surface points rather than points inside the
sphere.

I think there is some difficulty in accurately calculating whether a point
is inside or outside a polygon, if you submit a point which lies on or very
close to the surface due to round-off errors in the ray-tracing used.


Jothy

On Wed, Sep 29, 2010 at 12:23 PM, rakesh patil <prakeshofficial at gmail.com>wrote:

> hi,
>
> Below is the sample code what i was trying.
>
> int num = polyPd->GetNumberOfPoints();
> // polyPd is a polydata containing points that forms a polygon
>
> vtkPoints* points = this->del->GetOutput()->GetPoints();
> // del is an instance of vtkDelaunay2d class. Out of this object is used to
> display
> // scattered points
>
> vtkPoints *newPoints = vtkPoints::New();
> // To store selected points
>
> double bnds[6], n[3];
>
> // Get the bounds in 'bnds'
> polyPd->GetPoints()->GetBounds(bnds);
>
> // To get normal direction in 'n'
> vtkPolygon::ComputeNormal(num,
>   static_cast<double *>(polyPd->GetPoints()->GetData()->GetVoidPointer(0)),
> n);
>
> for( int id = 0; id < points->GetNumberOfPoints(); id++ )
> {
>   if( vtkPolygon::PointInPolygon( points->GetPoint(id), num,
>       static_cast<double
> *>(polyPd->GetPoints()->GetData()->GetVoidPointer(0)), n) == 1 )
>        newPoints->InsertNextPoint(points->GetPoint(id));
> }
>
> // code to create a mapper and actor with
> // the help of newPoints
>
> I hope there is no difficulty in understanding the other part of code. I
> got this logic from the mailing list when i searched for PoinInPolygon here
>
> http://public.kitware.com/pipermail/vtkusers/2010-April/107974.html
>
> Thanks
>
> Warm Regards
> Rakesh Patil
>
>
> On Wed, Sep 29, 2010 at 3:49 PM, Jothy <jothybasu at gmail.com> wrote:
>
>> Could you please post your code?
>>
>> Jothy
>>
>> On Wed, Sep 29, 2010 at 11:09 AM, rakesh patil <prakeshofficial at gmail.com
>> > wrote:
>>
>>> Hi,
>>>
>>> I have been trying to find whether a given point is within a polygon or
>>> not. I have been doing this using,
>>>
>>> vtkPolygon::PointInPolygon()
>>>
>>> function. But out of 10 runs, in 1 run, i get only few points inside, the
>>> polygon. Others just fails and shows 0 points selected.
>>>
>>> Can anyone come up with a small example, for this?
>>>
>>> Thanks
>>>
>>> Warm Regards
>>> Rakesh Patil
>>>
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>>
>>
>> --
>> PhD Student
>> Dept. of Medical Physics
>> Clatterbridge Centre for Oncology
>> UK
>>
>>
>


-- 
PhD Student
Dept. of Medical Physics
Clatterbridge Centre for Oncology
UK
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