[Paraview] PolyData bug??

Alejandro Aragon alejandro.aragon at gmail.com
Tue Apr 1 12:32:28 EDT 2008

If it is an expensive operation, it could be done only once when  
reading the input file and save the result as a flag for subsequent  
rendering. Again, I don't think it's a big deal and it prevents  
completely from doing scientific visualization if someone uses non- 
convex polygons. Imagine for some reason that I do CFD with non-convex  
finite volumes. How in the world am I going to see the elements????


On Apr 1, 2008, at 10:44 AM, Moreland, Kenneth wrote:

> I understand your sentiments, but the solution is not practical.  If  
> ParaView were primarily used for modeling, which deals with fewer,  
> more complicated elements, then I would totally agree with you.   
> However, scientific visualization typically deals with data  
> comprising many simple elements.
> Checking for convexity is an expensive operation on data that is  
> already tessellated.  This is a problem when using ParaView for  
> large data visualization, which is on of the major things it was  
> designed for.
> -Ken
>> -----Original Message-----
>> From: Alejandro Aragon [mailto:alejandro.aragon at gmail.com]
>> Sent: Tuesday, April 01, 2008 9:04 AM
>> To: Moreland, Kenneth
>> Cc: paraview at paraview.org
>> Subject: Re: [Paraview] PolyData bug??
>> I strongly disagree. The user shouldn't be aware of such a thing. If
>> Paraview gives you the option of drawing a polygon, it should be
>> independent on its convexity. What it should do, is to check if the
>> polygon is convex to use the regular GL function, and if not use
>> tessellation to draw it. I have done this myself in the past, so I
>> don't think it's a big deal.
>> aa
>> On Apr 1, 2008, at 9:06 AM, Moreland, Kenneth wrote:
>>> I don't think this is a bug.  OpenGL (and every other rendering
>>> system that I am aware of) assumes that its polygons are convex.
>>> You will have to tessellate your polygons into convex pieces in
>>> order for them to be rendered correctly.
>>> -Ken
>>>> -----Original Message-----
>>>> From: paraview-bounces at paraview.org [mailto:paraview-
>> bounces at paraview.org
>>>> ]
>>>> On Behalf Of Alejandro Aragon
>>>> Sent: Monday, March 31, 2008 10:31 PM
>>>> To: paraview at paraview.org
>>>> Subject: [Paraview] PolyData bug??
>>>> Hello everyone,
>>>> I was playing to see if I could write a complicated shape with
>>>> PolyData, and I found out that the visualization is really bad. The
>>>> surface and surface with edges visualizations don't look quite  
>>>> right.
>>>> I attached a wireframe and the surface with edges plots so you can
>>>> take a look. Some time back I got the same problem when I tried to
>>>> draw a polygon using OpenGL. I was able to solve the problem by  
>>>> using
>>>> tesselation, so I believe the same is happening here. I also  
>>>> attached
>>>> the vtp file. I'm on Mac OS, but I don't think that would make any
>>>> difference.
>>>> Cheers,
>>>> Alejandro Aragón

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