[vtkusers] Double precision in VTK

[egk865 at yahoo.com]

Thanks! Looking forward to it. One class I noticed that has a
vtkFloatArray hard coded into it is vtkPolyDataNormals. The normals
are computed as float even if the original vertices are double (besides
the vertices themselves which get truncated to float from double in
the output). I can't think of a reason why the algorithm would be
limited in precision if the vertices are in double, so I would think a
check should be done such that if the vertices are in double, the
normals are computed as double and float otherwise. This should apply
as well to other filters that generate point or cell attribute
data such as vtkTransformPolyDataFilter.

Also for source filters such as vtkSphereSource which don't have
inputs, I think there should be a way to specify the data type of the
output.

Thanks again,
Eli



> Date: Fri, 16 Apr 2010 20:12:12 -0400
> From: Berk Geveci <berk.geveci at kitware.com>
> Subject: Re: [vtkusers] Double precision in VTK
> To: "egk865 at yahoo.com"
> <egk865 at yahoo.com>
> Cc: vtkusers at vtk.org
> Message-ID:
>     <l2j45d654b1004161712n54293807gd6d53004ca90dcb at mail.gmail.com>
> Content-Type: text/plain; charset=ISO-8859-1
> 
> We are slowly moving towards preserving the native type of
> the input.
> There are some filters that are internally templated for
> this purpose.
> If you see ones that you think should be double precision,
> please
> report them. Note that not all filters need to produce
> double
> precision data. If an algorithm is inherently limited in
> precision, it
> is best to use floating point for performance reasons.
> 
> -berk
> 
> On Thu, Apr 15, 2010 at 10:55 AM, egk865 at yahoo.com
> <egk865 at yahoo.com>
> wrote:
> > Are there any plans to support double precision in VTK
> anytime soon?
> > It seems that much of VTK is optimized primarily for
> > single floating point precision with many filters
> hardcoded to output
> > data in single precision even when the input to them
> is in double
> > precision.
> >
> > One possible reason I can see why vtk may have been
> written
> > primarily with single precision in mind is that most
> modern
> > graphics cards are optimized for single precision and
> internally
> > store the data in single precision. However, not all
> applications
> > need to write to the graphics card and the ability for
> VTK to work
> > well with double precision data would be very useful
> especially for
> > science and research applications where accuracy is
> important.
> >
> > Thanks,
> > Eli
> >
> >
> >
> >
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