[vtkusers] implicit surface with polys qn..

[Sebastien BARRE]

At 25/10/00 14:04 -0400, K.R.Subramanian wrote:

>I have 2D contours from a series of consecutive image slices. I need to
>do the following:
>
>1. Connect them up into a polyhedral mesh (actually linear
>interpolation, which is polyhedral)
>2. I want to treat this like an implicit function, in particular, be
>able to do a membership test, inside
>     should be positive, outside should be negative, on the surface
>should be zero..
>
>The surface is open at both ends (like a bent pipe)
>
>As I am fighting a deadline,  if someone has done something similar, I
>would like to know
>the easiest way to do this using VTK.

I haven't done that but :

- I'm not sure about this but as soon as you have a polygonal set you 
probably might use vtkImplicitDataSet :
         vtkImplicitDataSet (Treat a dataset as if it were an implicit 
function)

- if you have access to the image slices, consider using marching-cubes 
like algorithm to extract the polygonal surface directly.

- you will probably have to close your surface at both ends

- a quick and dirty idea, i.e. convert your set of contours to cylindrical 
coordinates...
          for each 2D contour : compute the barycenter C, then send rays 
(on the contour plane) from that center toward the contour with an angle 
step = 5° (for example). The intersection points allow you to formulate 
your contour as a fonction of points defined by (distance, angle) pairs. 
Then connect the contours together using points that have the same angle. 
This is really dirty, and will fail on singularity, your contour better be 
convex.