[vtk-developers] A vtkDataSampler and image interpolation

David Gobbi david.gobbi at gmail.com
Tue Jul 5 12:51:36 EDT 2011


Hi Will,

So far I've only considered the filters that I use, mainly vtkProbeFilter and
the implicit functions vtkImplicitDataSet and vtkImplicitVolume.  And I've
also considered the possibility of a volume mapper that uses it, so that
people can provide their own specialized interpolation algorithms when they
are volume rendering their data.  However, my experience with VTK's more
sophisticated graphics algorithms like streamlines is close to nil... I would
have to rely on other people's expertise to make a full list.

 - David


On Tue, Jul 5, 2011 at 10:27 AM, Will Schroeder
<will.schroeder at kitware.com> wrote:
> Pretty cool idea David, thanks for the explanation.
> There are other potential filter applications that come to mind (as I'm sure
> you're aware of) such as streamlines, etc. Have you  created a list, or
> thought about, which filters might benefit from this capability?
> W
>
> On Tue, Jul 5, 2011 at 8:26 AM, David Gobbi <david.gobbi at gmail.com> wrote:
>>
>> Hi Will,
>>
>> If I modified the vtkProbeFilter to use the vtkDataSampler, it would
>> allow people to customize the way that vtkProbeFilter interpolates the
>> data.
>>
>> The interface would look like this: a SetDataSampler() method would be
>> added to vtkProbeFilter
>>
>> void vtkProbeFilter::SetDataSampler(vtkDataSampler *);
>>
>> The probe filter would have a default vtkDataSampler object which
>> would use FindCell to interpolate the data (much like the way
>> vtkProbeFilter works now).  But here is where the magic comes.  The
>> user would be able to provide a different data sampler:
>>
>> vtkImageSampler *isample = vtkImageSampler::New();
>> probeFilter->SetDataSampler(isample);
>>
>> The vtkImageSampler is for image data, it has interpolation code that
>> is specifically written for structured data and is orders of magnitude
>> faster than using FindCell to interpolate the data.  Also, it provides
>> the option of choosing different interpolation modes: nearest, linear,
>> and cubic.
>>
>> So, in a nutshell, adding a SetDataSampler() method would make it
>> possible for users to customize the way that vtkProbeFilter
>> interpolates values from its Input.  The use of vtkImageSampler here
>> is just one example, if a person needs to use vtkProbeFilter on an FEM
>> data set and knows of an efficient way to interpolate their FEM, then
>> they could write a vtkDataSampler class specifically for their FEM.
>>
>> Another way to describe my goal is as follows: I have a whole bunch of
>> image interpolation code that I've written and tweaked over the past
>> 10+ years, and I want to be able to use this interpolation code with
>> the VTK graphics pipeline.  The vtkDataSampler class is how I hope to
>> achieve this.
>>
>>  - David
>>
>>
>> On Tue, Jul 5, 2011 at 3:49 AM, Will Schroeder
>> <will.schroeder at kitware.com> wrote:
>> > David-
>> > What's the relationship of this vtkDataSampler class to the
>> > vtkProbeFilter?
>> > W
>> >
>> > On Mon, Jul 4, 2011 at 1:23 PM, David Gobbi <david.gobbi at gmail.com>
>> > wrote:
>> >>
>> >> Hi All,
>> >>
>> >> I've written some new interpolation classes for VTK, both for images
>> >> and for other data sets.  One thing that I want to ensure is that the
>> >> abstract interface is something that people will be satisfied with.
>> >> I use the same ScalarMode constants as vtkMapper, but there might
>> >> be a better way of selecting arrays that I am not aware of:
>> >>
>> >> class vtkDataSampler : public vtkObject
>> >> {
>> >>  // set the data to interpolate (does not establish pipeline
>> >> connection)
>> >>  void SetInput(vtkDataObject *);
>> >>
>> >>  // update any internal state variables prior to commencing
>> >> interpolation
>> >>  void Update();
>> >>
>> >>  // get an interpolated value, return "false" if out of bounds
>> >>  bool GetSample(const double point[3], double *value);
>> >>
>> >>  // get an interpolated value (meant for use by wrapper languages)
>> >>  double GetSample(double x, double y, double z, int component);
>> >>
>> >>  // set the scalar mode (same as vtkMapper scalar modes)
>> >>  void SetScalarMode(int mode);
>> >>  void SetScalarModeToDefault();
>> >>  void SetScalarModeToUsePointData();
>> >>  void SetScalarModeToUseCellData();
>> >>  void SetScalarModeToUsePointFieldData();
>> >>  void SetScalarModeToUseCellFieldData();
>> >>
>> >>  // set the array, if chosen scalar mode is field data
>> >>  void SetArrayName(const char *name);
>> >>
>> >>  void SetTolerance(double);
>> >>  void SetLocator(vtkLocator *locator);
>> >> };
>> >>
>> >> The changes are on gerrit, if people want to see the full
>> >> implementation:
>> >> http://review.source.kitware.com/2004
>> >>
>> >>  - David
>
>
>
> --
> William J. Schroeder, PhD
> Kitware, Inc.
> 28 Corporate Drive
> Clifton Park, NY 12065
> will.schroeder at kitware.com
> http://www.kitware.com
> (518) 881-4902
>



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