[vtkusers] Structured And Unstructured

[Andrea Gavana]

Hello NG,

     probably I did not understand clearly what is in VTK the difference 
between the Structured and Unstructured grids. By working in Reservoir 
Engineering application, these 2 words have different meaning wrt what VTK 
thinks...
     I've looked to the VTK examples, but I'm still missing something. I would 
like to display a 3D grid (coming from a finite difference discretization) 
using VTK; the geomtery of this grid is called "Corner Point", because cells 
are hexahedrons ("distorted" voxels); sometimes these cells are not connected 
between them (in presence of faults, discontinuities, what is called "non-
neighbor connections"). These grids are fully specified by giving the 
coordinates of the 8 corners of every cell (x,y,z value for every corner). In 
this way, I have a 10000 cell model, I end up with 80000 values for x, 80000 
for y and 80000 for z. In any case, these grid are still Structured. 
     So, my question is: am I missing something? If I am right and these grids 
are structured, in which order do I have to specify the grid coordinates? In 
natural order? Reverse order? Chaotic order? I didn't find anything about this. 
If I am not right and these grids are Unstructured (always following VTK 
specification), accordingly to the "VTK file format" pdf file, I have to 
specify EVERYTHING about these cells (type = 12 "hexahedron", number of 
corners, coordinates, connections, types...): is this really necessary? Is it 
not true that a grid is fully specified only by giving all the cell's corner 
coordinates? Is there a way to overcome all these difficulties? I don't see any 
practical way to calculate cell connections and other parameters that VTK 
REQUIRES to do visualization...

     Thanks a lot for every suggestion. Sorry for the long post and for my 
english...

Andrea.