[vtk-developers] Ghosts ???

[Amy Henderson]

Here's the general idea behind ghost cells, points, etc.  We're starting to 
deal with the possibility of poly data being broken into several 
pieces.  We may need to know that a point is shared between different 
pieces.  In this case, one piece will "own" the shared point, and the other 
pieces will have this point marked as a "ghost" point in their piece of the 
data.  For example, if we're doing a glyph on several pieces of data, and 
we don't want duplicate glyphs, then each piece only glyphs the points it 
owns and ignores those marked as ghost points.

In other cases, we need to know what's going on in cells neighboring those 
in our piece of the data.  These neighboring cells we have termed "ghost 
cells".  We also have the notion of multiple layers of ghost cells.  The 
cells in our piece of the data have ghost level 0.  Those cells that share 
a point with our piece have ghost level 1.  Those cells that share a point 
with the cells in level 1 have ghost level 2, and so on.  An example of a 
filter that we've modified to take advantage of ghost cells is 
vtkPolyDataNormals.

We keep track of the ghost level of a cell or point by adding an additional 
array to vtkDataObject called GhostLevels.

Amy

At 12:07 PM 8/16/2000 -0400, you wrote:
>Amy,
>I see a bunch of checkin's that have something to do with ghosts?
>
>If this is some new major feature, perhaps the vtk-developers should
>have some discussion?
>
>Bill
>
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