[vtkusers] formula for quadratic Non-linear cell types?

[David Thompson]

Hi Jeonggyu,

> Some of non-linear cell types are not clear to me. Certainly, it  
> should interpolate all control points however when I looked at  
> wireframe rendering it seems like they are just subdivided(without  
> any further alternation).

You may use the vtkTessellatorFilter to subdivide further.

> ... So I'd like to know where I can find the formula for Quadratic  
> Interpolation that VTK used. Can I use any interpolation function  
> that will pass through control points? If so, how many in-betweening  
> points do I put for each edge(perhaps 1)?

If you obtain a vtkGenericCell pointer (or the proper vtkCell subclass  
such as vtkQuadraticHexahedron) representing a cell in the mesh, you  
may call its EvaluateLocation method with parametric coordinates to  
obtain field values interpolated nonlinearly. The files implementing  
subclasses of vtkNonLinearCell contain the interpolation functions  
used for the elements. In general, you may not use any function that  
interpolates the control points since multiple parameterizations of  
elements are possible.

	David