[Paraview] Switching to parametric coordinates

[peter heppel]

Berk
This is a well-known problem and incidentally one for which I have an
implementation. 

In general you can map an open surface mesh to a plane without problems
(once you've dealt with an ill-conditioned matrix). In the literature you'll
see people have tried minimizing various properties of the surface in order
to make a 'good' parameterization. See for instance Desbrun, Meyer & Alliez
'intrinsic parameterizations of surface meshes' Eurographics 2002.

These approaches will give you some (UV) coordinates but I imagine that you
want a bit more than that: you want to map your mesh to a rectangle in
parameter space such as u=0, v=0 to u=1, v=1.

This is also easy to formulate and solve, provided that you know which
vertices are on which edge of the parameter space. But this is a user
choice. The filter must either ask the user to pick the corners, or apply
some user-defined heuristics to identify them. 

I'd be glad to make my code available as a vtk filter although as this will
be my first it will surely need careful reviewing. 

Cheers


Peter

Peter Heppel

35 Rue de locmalo
56290 PORT-LOUIS
France

02 97 82 19 30
06 81 30 76 52
skype : peterheppel

peter at peterheppel.com


 
 
  


-----Original Message-----
From: paraview-bounces at paraview.org [mailto:paraview-bounces at paraview.org]
On Behalf Of David E DeMarle
Sent: 09 November 2009 16:45
To: Berk Geveci
Cc: paraview at paraview.org
Subject: Re: [Paraview] Switching to parametric coordinates

I think your best bet is to provide u and v at the reader as a attribute
array.

I could be wrong (I'm not a topology or meshing expert) but I don't
think it is possible to in general provide a u,v mapping for arbitrary
shapes. If it is possible, it would be great to have the algorithm
coded up as a filter in VTK.

David E DeMarle
Kitware, Inc.
R&D Engineer
28 Corporate Drive
Clifton Park, NY 12065-8662
Phone: 518-371-3971 x109



On Mon, Nov 9, 2009 at 10:31 AM, Berk Geveci <berk.geveci at kitware.com>
wrote:
> Ah, I understand. There is no general solution to this problem in
> VTK/ParaView. Texture coordinates is probably closest. You can look at
> Texture map to ... filters. Essentially, you need to write a filter
> that computes the parametric coordinates for the kind of surface you
> are interested it.
>
> -berk
>
> On Mon, Nov 9, 2009 at 10:27 AM, Fred Fred <stan1313 at hotmail.fr> wrote:
>> I mean I would like for instance to have my surface colored by a function
of
>> u, u being the value of the parametric coordinate, given an origin on the
>> surface.
>> BTW using parametric coordinates in a filter would require having these
>> parametric coordinates available, which, for an arbitrary surface, would
>> involve computing it, so this is the same problem: how to compute those
>> parametric coordinates?
>>
>>> Date: Mon, 9 Nov 2009 09:04:53 -0500
>>> Subject: Re: [Paraview] Switching to parametric coordinates
>>> From: berk.geveci at kitware.com
>>> To: stan1313 at hotmail.fr
>>> CC: paraview at paraview.org
>>>
>>> I am not sure I understand what you mean. You want to use parametric
>>> coordinates inside a filter?
>>>
>>> On Sun, Nov 8, 2009 at 1:37 PM, Fred Fred <stan1313 at hotmail.fr> wrote:
>>> > I wonder if it is possible to switch to parametric coordinates, either
>>> > on a
>>> > curve or on a surface, given an arbitrary origin and arbitrary u or
>>> > (u,v)
>>> > unit vectors?
>>> >
>>> >
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