[vtk-developers] Class design for spline visualizations

[David Thompson]

Hi Lin,

I've just realized that the control points for Bézier patches will not have the same coordinates as the NURBs control points. That's because the Bézier patches interpolate their corner control points. So, we cannot just use a mapped data array to provide access to a subset of the NURBS control polygon.

This site:

  http://www.mactech.com/articles/develop/issue_25/schneider.html

describes the conversion process for curves in its "CONVERTING NURB TO BÉZIER CURVES" section. Basically, we need to implement knot insertion, which is described in Piegl's NURBS Book in Chapter 5.

The adaptor class shouldn't need to change much, but it might be better not to use a vtkMappedDataArray for the NURBS adaptor since it will have to generate new control points.

	David


> On Jun 19, 2015, at 7:04 PM, David Thompson <david.thompson at kitware.com> wrote:
> 
> Hi Lin,
> 
>> Does different patches in one vtkStructuredGrid have same order of interpolant and same number of control points? 
> 
> No, all the patches in a NURBs control polygon should have the same degree and control-point topology.
> 
>> Each patch should have its own knot vector, so number of patches = number of knot vectors.
> 
> Not quite. Each patch has a range of knot values. Those ranges overlap more as the degree increases.
> 
> 	David