[vtkusers] Unstructured grid to structured grid?
Chris Marsh
chris.marsh at usask.ca
Tue Sep 16 16:07:34 EDT 2014
No dice. With the examples code, I would get a blank plane uniform plane
with the data name 'elevation' as per the SetName() call. However, now, I
get no plane, and for coloring all I see (in paraview) is 'solid color' and
'elevation' is no longer present. Which suggests to me something else is
perhaps wrong?
On Tue, Sep 16, 2014 at 2:03 PM, David Gobbi <david.gobbi at gmail.com> wrote:
> 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.
> >>> >> >
> >>> >> >
> >>> >
> >>> >
> >>
> >>
>
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