[vtkusers] Unstructured grid to structured grid?
Aashish Chaudhary
aashish.chaudhary at kitware.com
Tue Sep 16 18:58:58 EDT 2014
I didn't follow the entire email but may be you can even try this filter
http://www.vtk.org/doc/release/4.0/html/classvtkGaussianSplatter.html#_details
for the purpose. You may have to adjust parameters.
- Aashish
On Tue, Sep 16, 2014 at 6:49 PM, Chris Marsh <chris.marsh at usask.ca> wrote:
> Aha! Excellent, thanks. This all seems to work, mostly.
>
> The interpolation doesn't look very good, even after increasing the
> resolution. As well, it is flipped along the y-axis. Image is a mountain,
> variable is air temp (blue = cold, red = warm).
> See here: http://imgur.com/l1KpcS0
>
> The code that converts my triangulation into the vtk format is shared
> between the mesh and plane code, so it should 'work' given the mesh is
> right.
>
> Secondly: I need to iterate over the rows/cols of this interpolated grid
> in order to write it to an ArcGIS ascii file. What would be the best way to
> do this? The fact it is now in a delaunay triangulation somewhat doesn't
> help (now that I think about it!)
>
> Thanks for all the help
>
> On Tue, Sep 16, 2014 at 2:12 PM, David Gobbi <david.gobbi at gmail.com>
> wrote:
>
>> You also have to call gridPoints->Update(), because you are getting
>> its output directly, rather than connecting to its output port.
>>
>> On Tue, Sep 16, 2014 at 2:07 PM, Chris Marsh <chris.marsh at usask.ca>
>> wrote:
>> > 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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--
*| Aashish Chaudhary | Technical Leader | Kitware Inc. *
*| http://www.kitware.com/company/team/chaudhary.html
<http://www.kitware.com/company/team/chaudhary.html>*
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