[vtkusers] Re: How to compute tangents and normals at each point of a curve ( vtkPolyData ) ???

[Goodwin Lawlor]

Deepak Roy wrote:
> Hello,
>  
> -- I am using vtk 4.4.
>  
> -- I have a triangular surface mesh as input vtkPolyData
>  
> -- I intersect the surface with a cartesian plane ( xy , yz or xz ) and 
> obtain a curve --- i use the vtkContourFilter to extract this curve.
>  
> -- The curve thus extracted is in the form of vtkPolyData.
>  
> -- /*Now how can I compute the curve normals and curve tangents at each 
> point on this curve ?*/
> // 
>     --- vtkPolyDataNormals filter does not work for curves according to 
> the documentation.
>  
>     --- Does anyone know if there is a VTK filter to achieve this task ?
>  
>     --- I tried computing the normals myself from the Lagrangian 
> Interpolation curve passing thru the point and its 1-neighbors.
>   
>     ------ But i faced one more problem - /*How do i find the 
> neighboring vertices of a point  in vtkPolyData? */
> // 
>     ----------- i tried vtkPolyData::GetPointCells() but this does not 
> seem to work for curves. Any ideas ????
>  
>  
> Thanks in Advance.
>  
> Regards,
>  
> Deepak Roy
>  


Hi Deepak,

Is this 
(http://www.bioengineering-research.com/vtk/vtkPolyLineCurvature.htm) 
the sort of thing you need? This class is based on pseudo code posted by 
Philip Batchelor. Actually, we've a couple of new classes for 
surface/polyline curvatures updated for vtk5.0 (they need to be checked 
and submitted...). The tangents, normals, and binormals are all 
calculated but not passed to the output- that would be easy to change 
though.

hth

Goodwin