[Paraview] holes in distributed polydata

[Moreland, Kenneth]

Burlen,

For the zoom in, you say there are no holes/lines, but in the image I see a grid of lines.  It looks like you have a bunch of little quads with spacing in between them.  Is this the case?  If so, then the "hole" artifacts you see on the bottom of the screen are probably simply aliasing artifacts.  They are places where the pixel happens to align right where the gap is.

I can't think of an easy way around this (other than to modify your data to remove the gaps, if that makes sense).  Anti-aliasing techniques such as oversampling or smoothing would probably fix the problem, but they would also break the parallel rendering so they are no good.

-Ken


On 12/5/09 12:18 AM, "burlen" <burlen.loring at gmail.com> wrote:

its ugly but I get a lot better performance by splitting the work up
dynamically with a small grain size. in the run shown below there are
only 16 processes but there are a whole lot of process boundaries.

I was able to reproduce it on a second system today.

these holes are pretty non-deterministic in where they show up. moving
the camera they can show up in different places. Which makes sense if
this is related to some parallel rendering/finite precision issue with
all those process boundaries. The small size of the quads are also a
factor, because I didn't ever notice it before when using larger quads.

I saved the data as a legacy file and opening it on my desktop there are
no issues, so its definitely a parallel only issue. Also running through
D3 seems to fix it, but the issue may still be there because with the
minimal number of process boundaries its much less likely to get the
camera in just the right position.

Berk Geveci wrote:
> Ouch. That's very distributed :-) Does the problem go away when you
> decrease the number of partitions?
>
> On Thu, Dec 3, 2009 at 10:55 AM, burlen <burlen.loring at gmail.com> wrote:
>
>> I'm seeing lines where the background shows through a surface polydata of
>> quads. When I zoom into the region to investigate the holes are gone. Moving
>> the image around the holes appear in different places. They depend on camera
>> position. In this surface there are 2.5E6 quads. the area is 10x16 units and
>> the number of quads is 1250x2000. each quad has 0.008 units on a side. I
>> hadn't seen the holes before going to this higher resolution. It's likely
>> that the hole is near a process boundary, in my polydata filter each process
>> adds his quads to his output polydata, in this run the quads are distributed
>> in strips of 512 as needed.
>>
>> 3 holes/lines in bottom half of the image (black background shows through):
>> http://nashi-submaster.ucsd.edu/movies/PV/bug.png
>>
>> zoom in no holes/lines:
>> http://nashi-submaster.ucsd.edu/movies/PV/bug-zoom-2.png
>>
>> process boundaries (from process id filter):
>> http://nashi-submaster.ucsd.edu/movies/PV/bug-procs.png
>>
>> Should PV be able to handle a polydata distributed like this?
>>
>>
>>
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   ****      Kenneth Moreland
    ***      Sandia National Laboratories
***********
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