[vtkusers] Unstructured grid to structured grid?

[David Gobbi]

Oops, the second "SetPoint1" should be "SetPoint2".

On Tue, Sep 16, 2014 at 2:02 PM, David Gobbi <david.gobbi at gmail.com> wrote:
> 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.
>>> >> >
>>> >> >
>>> >
>>> >
>>
>>