[vtk-developers] DoublePi proposal

Mon May 14 12:50:38 EDT 2012

David,

Can you point me to the gerrit topic? If not, I can start from scratch.

Bill

On Mon, May 14, 2012 at 12:48 PM, David Gobbi <david.gobbi at gmail.com> wrote:
> If you could take it over, I would be overjoyed.
> For me, it was solidly on the back burner.
>
>  - David
>
>
> On Mon, May 14, 2012 at 10:38 AM, Bill Lorensen <bill.lorensen at gmail.com> wrote:
>> David,
>>
>> I'd like to revive this topic. I'm willing to take it over and track
>> down the regression failures.
>>
>> A quick survey of (only .cxx) files:
>> vtkMath::Pi() - 64 files
>> vtkMath::TwoPi() - 0
>> vtkMath::DoublePi() - 13
>> vtkMath::DoubleTwoPi() = 4
>> 3.1415... - 19
>> 6.2631... - 5
>>
>> Bill
>>
>> On Wed, Apr 18, 2012 at 11:22 AM, David Gobbi <david.gobbi at gmail.com> wrote:
>>> An update on changing vtkMath::Pi() so that it returns "double"
>>> instead of "float":
>>>
>>> I pushed a patch to gerrit that implemented this change, but the
>>> extra precision causes a few tests to fail.  Many of the sources and
>>> parametric functions in VTK use vtkMath::Pi(), and the few extra
>>> digits of precision cause them to produce slightly different results.
>>> Because not all tests are running with VTK 6 yet, I checked for test
>>> failures with a patched VTK 5.10.  The following tests failed:
>>>
>>> CellLocator - ERROR: 202 ray-sphere intersections missed!!!
>>> progGlyphsBySource - central glyph is missing a piece
>>> SurfacePickerWithTexture - slight texture map change
>>> TexturedSphere - ditto (i.e. exactly the same diff)
>>> TestConeLayoutStrategy - small differences in text positions
>>>
>>> The last three failures are of the expected kind, i.e. slight changes
>>> in positions due to added precision.  The CellLocator test failure
>>> is probably similar, but I need to investigate it further.  The
>>> progGlyphsBySource error is the most confusing one... it might
>>> just be a depth buffer issue, or it could be a math error in the
>>> vtkSuperquadricSource.
>>>
>>> In any case, I think that I'll have to delay the merge until all the
>>> tests are running again.
>>>
>>>  - David
>>>
>>> On Thu, Mar 1, 2012 at 10:14 AM, Marcus D. Hanwell
>>> <marcus.hanwell at kitware.com> wrote:
>>>> +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
>>>>>>> >>>> _______________________________________________
>>>>>>> >>>> Powered by www.kitware.com
>>>>>>> >>>>
>>>>>>> >>>> Visit other Kitware open-source projects at
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>>>>>>> >>>>
>>>>>>> >>>
>>>>>>> >>>
>>>>>>> >>>
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>>>>>>> >>>
>>>>>>> >>
>>>>>>> >>
>>>>>>> >>
>>>>>>> >> --
>>>>>>> >> +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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