[vtkusers] Re: [vtk-developers] contour lines and scalar color plot issues with vtkUnstructuredGrid

[Randall Hand]

On 2/15/06, Burlen <burlen at apollo.sr.unh.edu> wrote:
>
>
> It seems to me that the problem of open contours might be caused by the
> algorithm(s) used with unstructuredGrids built with the append filter.
> Could
> it have somehting to do with the fact that the boxes in my case are
> appended
> in a "willy nilly" order? adjacent boxes aren't necessarily appended one
> after the other.
>
>
I think this is the cause of your problem.  The vtkAppendFilter does not
"stitch" neighboring datasets along their boundaries, it keeps each dataset
as an individual piece.  So when you extract an isosurface from the combined
dataset, there is no connectivity along those inter-dataset boundaries,
leading to the "discontinuity" along the edges.  I've run into the same
issue here doing similiar things (reading a multi-block Plot3d file & using
AppendDataset to only have 1 vtkDataSet to pass around).

How to fix this?  I haven't the slightest, short of writing custom code to
replace vtkAppendDataset and do the stitching.  You may be able to Resample
the Data into a rectilinear form (use the ProbeFilter with an ImageData
input), and then get the Isosurface you want, but you'll have to live with
the resolution tradeoffs.  It'll also be sloooooow....


--
Randall Hand
Visualization Scientist,
ERDC-MSRC Vicksburg, MS
Homepage: http://www.yeraze.com
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