[vtk-developers] A vtkDataSampler and image interpolation

[Will Schroeder]

Okay thanks, assuming we document this in some manner (wiki or VTK Journal
article) let's put a placeholder for some other potential algorithms. I know
in DTI and other medical applications they are computing "streamlines" so
this could be very useful for medical image analysis.
W

On Tue, Jul 5, 2011 at 12:51 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> 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
> >
>



-- 
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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