[vtk-developers] vtkPentagonalPrism Bug

[Berk Geveci]

I CC'ed Jean, who seems to be the true original author of this code. Maybe
he'll have something to add.

-berk

On Tue, Jun 9, 2015 at 9:07 AM, Bill Lorensen <bill.lorensen at gmail.com>
wrote:

> There was a change made a while back to force the sum of the weights
> to be 1 and drives to be 0. I believe that change is flawed.
>
> But, the original code also fails to compute a valid center point. If
> I normalize the weights, the center is computed properly, but the
> EvaluatePosition code that uses the derivatives fails.
>
> On Tue, Jun 9, 2015 at 8:38 AM, Mathieu Malaterre
> <mathieu.malaterre at gmail.com> wrote:
> > Hi Bill,
> >
> > I wrote that a long time ago. I used the same approach in the 5-case and
> the
> > 6-case. So formulation should be very similar in the other prism (hexa
> one).
> > Since the points are chosen on a circle, I do not understand why it would
> > fail your test.
> >
> > Are the formulations the same, or were they changed by someone else ?
> >
> > -2cts
> >
> > On Tue, Jun 9, 2015 at 2:26 PM, Bill Lorensen <bill.lorensen at gmail.com>
> > wrote:
> >>
> >> Andrew,
> >>
> >> It is definitely as issue with the shape functions. I have played with
> >> them a bit and also looked for info on the web. I believe the sf's
> >> should sum to 1. But currently they only sum to one at the vertices of
> >> the cell.
> >>
> >> I made a change to normalize them each time they are computed. That
> >> fixes the computed center issue, but causes other problems.
> >>
> >> I'm hoping one of the original authors will respond.
> >>
> >> Thanks for looking at  it,
> >>
> >> Bill
> >>
> >> On Tue, Jun 9, 2015 at 3:14 AM, Andrew Maclean
> >> <andrew.amaclean at gmail.com> wrote:
> >> > Hi Bill,
> >> >    I played around with it today and I am pretty sure that the problem
> >> > lies
> >> > with the EXPRA ... EXPRN defines in vtkPentagonalPrism.cxx. These are
> >> > used
> >> > in InterpolationFunctions(), InterpolationDerivs().
> >> >
> >> > EvaluateLocation() uses InterpolationFunctions()  to determine the
> >> > weights.
> >> >
> >> > I don't understand the mathematical basis for the calculation of these
> >> > and a
> >> > web search has not revealed anything.
> >> >
> >> > Regards
> >> >     Andrew
> >> >
> >> >>
> >> >> ---------- Forwarded message ----------
> >> >> From: Bill Lorensen <bill.lorensen at gmail.com>
> >> >> To: VTK Developers <vtk-developers at vtk.org>
> >> >> Cc: Mathieu Malaterre <mathieu.malaterre at gmail.com>
> >> >> Date: Sun, 7 Jun 2015 14:40:27 -0400
> >> >> Subject: Re: [vtk-developers] vtkPentagonalPrism Bug
> >> >> Sorry, the posted code was incorrect, but the results are still
> >> >> wrong...
> >> >>
> >> >>
> >> >> On Sat, Jun 6, 2015 at 12:48 PM, Bill Lorensen
> >> >> <bill.lorensen at gmail.com>
> >> >> wrote:
> >> >> > Folks,
> >> >> >
> >> >> > I've been working on a Unit test for linear cells. So far I have
> >> >> > found
> >> >> > a few bugs that I could easily fix.
> >> >> >
> >> >> > My testing has uncovered a problem with vtkPentagonalPrism that I
> >> >> > cannot fix on my own.
> >> >> >
> >> >> > If I compute the real center from the parametric center, the real
> >> >> > center is not within the bounds of the cell. This is the only cell
> >> >> > that fails this test.
> >> >> >
> >> >> > I have attached a small program and cmake file that illustrates the
> >> >> > problem.
> >> >> >
> >> >> > Bill
> >> >>
> >> >>
> >> >>
> >> >> --
> >> >> Unpaid intern in BillsBasement at noware dot com
> >> >>
> >> >>
> >> > --
> >> > ___________________________________________
> >> > Andrew J. P. Maclean
> >> >
> >> > ___________________________________________
> >>
> >>
> >>
> >> --
> >> Unpaid intern in BillsBasement at noware dot com
> >
> >
> >
> >
> > --
> > Mathieu
>
>
>
> --
> Unpaid intern in BillsBasement at noware dot com
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