[vtkusers] Terrain rendering problem

[Georgios Katsaros]

Thanks Chris,

Since the terrain source creates triangle strips itself,
I'm not using vtkStripper. I have used vtkDecimatePro,
without any effect on the specific problem.

Just to try things out, I modified the code to create triangles
instead of triangle strips, and then viewed the result with and 
without the stripper. Besides performance, there was little difference 
in the output.

Finally, I've attached two jpg images that show the problem.
Notice how the flat, noisy-looking parts of the top view
correspond to terrain extrusions in the bottom view. These
extrusions are actually valleys that should be visible from the top.

Any comments on the cause of such an effect would be greatly appreciated.
Original post:
http://www.vtk.org/pipermail/vtkusers/2004-February/021962.html

Thanks again,
George.


Chris Scharver wrote:
> 
> On Feb 3, 2004, at 10:14 AM, Georgios Katsaros wrote:
> 
> > The result is "almost" correct, except for the following intermittent
> > problem: When the "edges" of the terrain data are of higher elevation
> > than data closer to the center of the terrain patch, the internal data
> > is rendered "underneath" the terrain. So, instead of having a "valley"
> > in the middle of the terrain, there is a "mountain" under the terrain
> > model. The "valley" on the upper face is rendered as flat, with some
> > straight-line patterns.
> > On the other hand, an island (where surrounding elevations are zero),
> > renders correctly.
> 
> We have noticed similar problems using vtkStripper on some triangle
> geometry. Edges, especially those that are higher than adjacent
> "internal" vertices, show sharp visual artifacts. Can you check the
> output of your pipeline before applying the stripper? It will be a lot
> slower, but see if those same visual artifacts are present. Our
> short-term workaround has been to simply not strip the data, which is a
> far from ideal solution.
> 
> Chris
> --
> Chris Scharver
> Electronic Visualization Laboratory
> The University of Illinois at Chicago
> Ph: 312-996-3002   FAX: 312-413-7585
> <http://www.evl.uic.edu/scharver/>
> 
> _______________________________________________
> This is the private VTK discussion list.
> Please keep messages on-topic. Check the FAQ at: <http://public.kitware.com/cgi-bin/vtkfaq>
> Follow this link to subscribe/unsubscribe:
> http://www.vtk.org/mailman/listinfo/vtkusers
-------------- next part --------------
A non-text attachment was scrubbed...
Name: TopView.jpg
Type: image/jpeg
Size: 25406 bytes
Desc: not available
URL: <http://www.vtk.org/pipermail/vtkusers/attachments/20040203/698ae0db/attachment.jpg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: BottomView.jpg
Type: image/jpeg
Size: 26047 bytes
Desc: not available
URL: <http://www.vtk.org/pipermail/vtkusers/attachments/20040203/698ae0db/attachment-0001.jpg>