[vtkusers] Unstructured grid to structured grid?

[David Gobbi]

The default plane size is 1x1, so you might need this:

    gridPoints->SetResolution(gridSize, gridSize);
    gridPoints->SetOrigin(0, 0, 0);
    gridPoints->SetPoint1(gridSize, 0, 0);
    gridPoints->SetPoint1(0, gridSize, 0);

On Tue, Sep 16, 2014 at 1:49 PM, Chris Marsh <chris.marsh at usask.ca> wrote:
> Hi David,
>
> To clarify: I want to take an unstructured grid (x,y) with face data (z) and
> make it a 2D structured grid. I have connectivity information
> (triangulation).
>
> Looking at vtkPlaneSource: looks like it should work/make my life easier
>
> However, even with the above linked demo with the slight modification, I
> cannot make this work. This is most likely a PEBKAC as a result of my lack
> of familiarity with VTK so I appreciate you taking the time to help. The
> minimum working example is below, based upon this code
> http://www.itk.org/Wiki/VTK/Examples/Cxx/PolyData/InterpolateMeshOnGrid
>
> vtkSmartPointer<vtkPoints> points = vtkSmartPointer<vtkPoints>::New();
>     vtkSmartPointer<vtkFloatArray>  data  =
> vtkSmartPointer<vtkFloatArray>::New();
>     data->SetName("elevation");
>
>     unsigned int gridSize = 10;
>     float maxHeight = 5;
>     for ( unsigned int i = 0; i < 100; ++i )
>     {
>         double x = vtkMath::Random(0, gridSize);
>         double y = vtkMath::Random(0, gridSize);
>         double z = vtkMath::Random(0, maxHeight);
>     points->InsertNextPoint ( x, y, 0);
>     data->InsertNextValue(z);
>     }
>
>     // Add the grid points to a polydata object
>     vtkSmartPointer<vtkPolyData> polydata =
> vtkSmartPointer<vtkPolyData>::New();
>     polydata->SetPoints ( points );
>     polydata->GetPointData()->SetScalars(data);
>
>     // Triangulate the grid points. If you do not have a mesh (points
>     // only), the output will not be interpolated!
>     vtkSmartPointer<vtkDelaunay2D> tri =
> vtkSmartPointer<vtkDelaunay2D>::New();
>     tri->SetInputData ( polydata );
>     tri->Update();
>
>     // Create a grid of points to interpolate over
>     vtkSmartPointer<vtkPlaneSource> gridPoints =
> vtkSmartPointer<vtkPlaneSource>::New();
>     gridPoints->SetResolution(gridSize, gridSize);
>     gridPoints->SetOrigin(0,  0, 0);
>
>     // Perform the interpolation
>     vtkSmartPointer<vtkProbeFilter> probeFilter =
> vtkSmartPointer<vtkProbeFilter>::New();
>     probeFilter->SetSourceConnection(tri->GetOutputPort());
>     probeFilter->SetInputData(gridPoints->GetOutput()); //
>     // Interpolate 'Source' at these points
>     probeFilter->Update();
>
>     vtkSmartPointer<vtkDelaunay2D> gridDelaunay =
> vtkSmartPointer<vtkDelaunay2D>::New();
>     gridDelaunay->SetInputConnection ( probeFilter->GetOutputPort() );
>
>     vtkSmartPointer<vtkXMLPolyDataWriter> gridWriter =
> vtkSmartPointer<vtkXMLPolyDataWriter>::New();
>     gridWriter->SetFileName ( "gridSurface.vtp" );
>     gridWriter->SetInputConnection ( gridDelaunay->GetOutputPort() );
>     gridWriter->Write();
>
>
>
>
> On Tue, Sep 16, 2014 at 12:07 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>
>> If you want to create a polydata that is a regular grid, then
>> use vtkPlaneSource with SetResolution(gridSize, gridSize).
>>
>> If you want your regular grid to be a vtkImageData, then
>> use vtkImageGridSource with SetDataExtent(), SetDataSpacing(),
>> an SetDataOrigin() to create the needed dimensions.
>>
>> Note that if your point cloud is just points without any connectivity
>> between the points (i.e. without any cells), then you cannot use
>> vtkProbeFilter.
>>
>>
>>
>>
>> On Tue, Sep 16, 2014 at 11:52 AM, Chris Marsh <chris.marsh at usask.ca>
>> wrote:
>> > Mmh thanks. I think I'll stick with the probe filter.
>> >
>> > I've been able to get  this example working
>> > http://www.itk.org/Wiki/VTK/Examples/Cxx/PolyData/InterpolateMeshOnGrid
>> > if I have a real-world pt cloud, I'm a bit unclear how I should make the
>> > grid.
>> >
>> > If xll and yll are the lower x and y coordinates of an axis aligned
>> > bounding
>> > box
>> >
>> > size_t gridSize = 100;
>> >     for ( size_t x = 0; x < gridSize; x++ )
>> >     {
>> >         for ( size_t y = 0; y < gridSize; y++ )
>> >         {
>> >             gridPoints->InsertNextPoint ( x+xll, y+yll, 0);
>> >         }
>> >     }
>> >
>> > does not seem to produce any output.
>> >
>> > Any suggestions?
>> >
>> > On Mon, Sep 15, 2014 at 4:39 PM, David Gobbi <david.gobbi at gmail.com>
>> > wrote:
>> >>
>> >> Another filter that might work is vtkShepardMethod, which takes
>> >> unstructured points (e.g. an arbitrary set of samples) as input and
>> >> produces a vtkImageData as output.
>> >>
>> >> The difference between vtkProbeFilter and vtkShepardMethod is
>> >> that the former performs the interpolation based on the connectivity
>> >> of the points (i.e. based on the cells), while the latter ignores the
>> >> connectivity and does the interpolation purely based on distance.
>> >>
>> >>  - David
>> >>
>> >> On Mon, Sep 15, 2014 at 4:23 PM, Chris Marsh <chris.marsh at usask.ca>
>> >> wrote:
>> >> > Thanks David, this looks perfect.
>> >> >
>> >> >
>> >> > On Mon, Sep 15, 2014 at 4:10 PM, David Gobbi <david.gobbi at gmail.com>
>> >> > wrote:
>> >> >>
>> >> >> Hi Chris,
>> >> >>
>> >> >> This sounds like a job for vtkProbeFilter.  The probe filter takes
>> >> >> two
>> >> >> inputs,
>> >> >> the "input" and the "source".  The idea is that it resamples the
>> >> >> scalars
>> >> >> from
>> >> >> the "source" onto the geometry of the "input".  So, in this case,
>> >> >> the
>> >> >> "source"
>> >> >> is your unstructured grid, and the "input" is any vtkImageData that
>> >> >> has
>> >> >> the
>> >> >> origin, spacing, and extent that you want to use for the regridding.
>> >> >> The
>> >> >> output of vtkProbeFilter will be an image that has the same geometry
>> >> >> as
>> >> >> the input, but that has pixel values that have been interpolated
>> >> >> from
>> >> >> your
>> >> >> unstructured grid.  You should be able to find several examples on
>> >> >> the
>> >> >> wiki.
>> >> >>
>> >> >>  - David
>> >> >>
>> >> >>
>> >> >> On Mon, Sep 15, 2014 at 3:59 PM, chrism <chris.marsh at usask.ca>
>> >> >> wrote:
>> >> >> > Is it possible to (easily) convert an unstructured grid to a
>> >> >> > structured
>> >> >> > grid
>> >> >> > (Image data)?
>> >> >> >
>> >> >> > Is unstructured -> polydata -> image data  the only way? If so,
>> >> >> > how
>> >> >> > example
>> >> >> >
>> >> >> >
>> >> >> > (http://www.vtk.org/Wiki/VTK/Examples/Cxx/PolyData/DataSetSurfaceFilter
>> >> >> > ??)
>> >> >> >
>> >> >> > Ultimately, the unstructured grid represents a topography, and I
>> >> >> > am
>> >> >> > looking
>> >> >> > to 'rasterize' it for use in a GIS.
>> >> >
>> >> >
>> >
>> >
>
>