[vtk-developers] DoublePi proposal

Thu Mar 1 12:14:34 EST 2012

+1 on the DoublePi to Pi with double proposal, seems like a good place
to clean up.

On Thu, Mar 1, 2012 at 11:46 AM, Philippe Pebay
<philippe.pebay at kitware.com> wrote:
> Agreed.
>
> Philippe
>
>
> On Thu, Mar 1, 2012 at 4:44 PM, Berk Geveci <berk.geveci at kitware.com> wrote:
>>
>> +1
>>
>> I would get rid of DoublePi in 6.0 since we are cleaning up so much stuff.
>>
>> On Thu, Mar 1, 2012 at 12:57 AM, David Gobbi <david.gobbi at gmail.com>
>> wrote:
>>>
>>> Well, I looked through VTK to see how vtkMath::Pi() was being used,
>>> and now I don't think that there is any reason for a single-precision
>>> pi at all.  In VTK 6, vtkMath::Pi() should return a double-precision
>>> value, period.
>>>
>>> I found 62 classes that call vtkMath::Pi().  Only one of them,
>>> vtkExodusReader, seemed to have a reason for using a single-precision
>>> value.  The others should have switched to vtkMath::DoublePi() a long
>>> time ago.  My only guess as to why they weren't is that they were
>>> missed during the big float-to-double conversion that occurred when
>>> VTK 4.4 was released.
>>>
>>> So my new proposal is to do nothing for VTK 5.10 (because
>>> vtkMath::FloatPi() isn't really needed for anything), but to still
>>> change vtkMath::Pi() to "double" for VTK 6.  Then eventually
>>> vtkMath::DoublePi() can be deprecated.
>>>
>>>  - David
>>>
>>>
>>>
>>> On Wed, Feb 29, 2012 at 5:17 PM, David Gobbi <david.gobbi at gmail.com>
>>> wrote:
>>> > Hi J-C,
>>> >
>>> > All of those are good examples of why vtkMath:Pi() should be
>>> > returning double instead of float... in each of those four locations,
>>> > a double-precision Pi should be used instead of a single-precision Pi.
>>> > So don't changed them to FloatPi().
>>> >
>>> > I've also noticed that many of the vtkParametricFunction subclasses in
>>> > VTK are using vtkMath::Pi() when they should be using  double-precision
>>> > pi.
>>> >
>>> >  - David
>>> >
>>> >
>>> > On Wed, Feb 29, 2012 at 4:44 PM, Jean-Christophe Fillion-Robin
>>> > <jchris.fillionr at kitware.com> wrote:
>>> >> Within Slicer vtkMath::Pi() is called at four location.  See details
>>> >> below.
>>> >>
>>> >> We will make sure to use vtkMath::FloatPi() when we will integrate VTK
>>> >> 5.10.
>>> >>
>>> >> Thanks
>>> >> Jc
>>> >>
>>> >>
>>> >>
>>> >> Modules/Loadable/Annotations/VTKWidgets/vtkAnnotationGlyphSource2D.cxx
>>> >> 352:  theta = 2.0 * vtkMath::Pi() / 8.0;
>>> >>
>>> >> Libs/MRML/Logic/vtkMRMLSliceLogic.cxx
>>> >> 2128:    double
>>> >> axisMisalignmentDegrees=acos(dotProd)*180.0/vtkMath::Pi();
>>> >>
>>> >> Libs/vtkTeem/vtkPreciseHyperStreamline.cxx
>>> >> 591:  vtkFloatingPointType
>>> >> theta=2.0*vtkMath::Pi()/this->NumberOfSides;
>>> >>
>>> >> Base/Logic/vtkSlicerGlyphSource2D.cxx
>>> >> 346:  theta = 2.0 * vtkMath::Pi() / 8.0
>>> >>
>>> >>
>>> >> On Wed, Feb 29, 2012 at 6:41 PM, Jean-Christophe Fillion-Robin
>>> >> <jchris.fillionr at kitware.com> wrote:
>>> >>>
>>> >>> +1 :)
>>> >>>
>>> >>>
>>> >>> On Wed, Feb 29, 2012 at 4:57 PM, David Gobbi <david.gobbi at gmail.com>
>>> >>> wrote:
>>> >>>>
>>> >>>> Hi All,
>>> >>>>
>>> >>>> I'm wondering if, for VTK 6, we can make the vtkMath::Pi() return a
>>> >>>> double instead of a float.  Currently, most VTK code is calling
>>> >>>> vtkMath::DoublePi() and, in my opinion, vtkMath::Pi() is more
>>> >>>> readable.
>>> >>>>
>>> >>>> Here's my proposal:
>>> >>>>
>>> >>>> 1) In VTK 5.10, a vtkMath::FloatPi() method would be added.  Any VTK
>>> >>>> 5.10 code that calls vtkMath::Pi() would be changed to call
>>> >>>> vtkMath::FloatPi() instead.
>>> >>>>
>>> >>>> 2) In VTK 6, vtkMath::Pi() would be changed so that it returns
>>> >>>> double,
>>> >>>> and then all instances of vtkMath::DoublePi() can be changed to
>>> >>>> vtkMath::Pi() to improve readability.
>>> >>>>
>>> >>>> If anyone thinks this is a good idea, I can submit a patch for the
>>> >>>> VTK
>>> >>>> 5.10 changes to gerrit.
>>> >>>>
>>> >>>>
>>> >>>> To reiterate what I'm proposing, in VTK 5.10, the following methods
>>> >>>> would
>>> >>>> exist:
>>> >>>>
>>> >>>> double vtkMath::DoublePi();
>>> >>>> float vtkMath::Pi();
>>> >>>> float vtkMath::FloatPi();  - new method for single precision
>>> >>>>
>>> >>>> In VTK 6.0, the following methods would exist:
>>> >>>>
>>> >>>> double vtkMath::DoublePi();
>>> >>>> double vtkMath::Pi();
>>> >>>> float vtkMath::FloatPi();
>>> >>>>
>>> >>>>  - David
>>> >>>> _______________________________________________
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>>> >>>>
>>> >>>
>>> >>>
>>> >>>
>>> >>> --
>>> >>> +1 919 869 8849
>>> >>>
>>> >>
>>> >>
>>> >>
>>> >> --
>>> >> +1 919 869 8849
>>> >>
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>>
>>
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>
>
>
> --
> Philippe Pébay, PhD
> Director of Visualization and High Performance Computing /
> Directeur de la Visualisation et du Calcul Haute Performance
> Kitware SAS
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