[vtkusers] Simple question

[Takaya Naoko]

To VTK users,

Hello! After getting the hang of Vtk( only the basics ), 
I tried to make my own program but can't go any further...

I'm trying to visualize a volume from the equation.
For example, in the Vtk text there was an example of 
visualizing a sphere from sphere equation( x^2+y^2+z^2-r^2=0)
but this is only the surface. I want the inside too and 
want to be able to visualize a part of it and see
the inside stuffed.

I don't know how to do that and looked through some of the
examples but the program all reads from .vtk files,
so I don't know how to do it. 

If any of you could send me a sample of visualizing the
volume data of the sphere using equations will be most
helpful :) ( if possible in C++ )

This might be a very easy thing to do, but for me
who just got started with vtk and not good at
programming, this is quite a hard thing to do :(

Thank you in advance!

Naoko Takaya from Japan