[vtkusers] Intersection of plane with 3D surface using vtkCutter

[Bill Lorensen]

You need a vtkPlane, not a vtkPlaneSource to do the cutting. The
vtkPlaceSource produces polydata. The vtkPlane is an implicit function.
vtkCutter uses implicit functions to cut the data.




On Thu, Aug 1, 2013 at 11:46 AM, Daniël Lacko <lacko.daniel at outlook.com>wrote:

> Hi all,
>
> I'm trying to calculate the circumference of the human head in 3D. I'm
> using VTK 5.10.1 and Python 2.7 64-bit. I want to calculate the
> intersection of a plane passing through certain point on the head. I then
> want to extract the boundary and calculate the length of this polyline.
> First, I want to visualize the boundary to make sure the extraction is
> working as expected.
>
> As far as I understand, I can use vtkCutter to cut a slice from the
> original image. When I modify the vtkCutter ClipCow.py example, I can use
> vtkFeatureExtract to extract the boundary and write it to a .vtk file for
> visualization:
>
>     # Here we are cutting the cow. Cutting creates lines where the cut
>     # function intersects the model. (Clipping removes a portion of the
>     # model but the dimension of the data does not change.)
>     #
>     # The reason we are cutting is to generate a closed polygon at the
>     # boundary of the clipping process. The cutter generates line
>     # segments, the stripper then puts them together into polylines. We
>     # then pull a trick and define polygons using the closed line
>     # segments that the stripper created.
>     cutEdges = vtk.vtkCutter()
>     cutEdges.SetInputConnection(cow.GetOutputPort())
>     cutEdges.SetCutFunction(plane)
>     cutEdges.GenerateCutScalarsOn()
>     cutEdges.SetValue(0, 0.5)
>     cutStrips = vtk.vtkStripper()
>     cutStrips.SetInputConnection(cutEdges.GetOutputPort())
>     cutStrips.Update()
>     cutPoly = vtk.vtkPolyData()
>     cutPoly.SetPoints(cutStrips.GetOutput().GetPoints())
>     cutPoly.SetPolys(cutStrips.GetOutput().GetLines())
>
>     # Extract boundary from cutPoly
>     cutBoundary = vtk.vtkFeatureEdges()
>     cutBoundary.SetInput(cutPoly)
>     cutBoundary.Update()
>     # Write cut line to .vtk file
>     polyWriter = vtk.vtkPolyDataWriter()
>     polyWriter.SetInput(cutBoundary.GetOutput())
>     polyWriter.SetFileName("cutPoly.vtk")
>     polyWriter.Write()
>
> The code works as intended. However, if I try using it with my own code,
> it won't read the surface data correctly:
>
>     # Circumference plane (used to cut)
>     circPlaneSource = vtk.vtkPlaneSource()
>     circPlaneSource.SetOrigin(G -
>             150*self.midSagittalPlaneNormal)
>     circPlaneSource.SetPoint1(Op -
>             150*self.midSagittalPlaneNormal)
>     circPlaneSource.SetPoint2(G +
>             150*self.midSagittalPlaneNormal)
>     circPlaneSource.SetResolution(15, 15)
>     circPlaneSource.Update()
>
>     surface = vtk.vtkSTLReader()
>     surface.SetFileName(fileName)
>
>     # Cut a slice out of the surface and convert it to a PolyData object
>     cutEdges = vtk.vtkCutter()
>     cutEdges.SetInputConnection(surface.GetOutputPort())
>     cutEdges.SetCutFunction(circPlaneSource.GetOutput())
>     cutEdges.GenerateCutScalarsOn()
>     cutEdges.SetValue(0, 0.5)
>     cutStrips = vtk.vtkStripper()
>     cutStrips.SetInputConnection(cutEdges.GetOutputPort())
>     cutStrips.Update()
>     cutPoly = vtk.vtkPolyData()
>     cutPoly.SetPoints(cutStrips.GetOutput().GetPoints())
>     cutPoly.SetPolys(cutStrips.GetOutput().GetLines())
>
>     # Extract boundary from cutPoly
>     cutBoundary = vtk.vtkFeatureEdges()
>     cutBoundary.SetInput(cutPoly)
>     cutBoundary.Update()
>
>     # Write cut line to .vtk file
>     polyWriter = vtk.vtkPolyDataWriter()
>     polyWriter.SetInput(cutBoundary.GetOutput())
>     polyWriter.SetFileName("test.vtk")
>     polyWriter.Write()
>
> I don't get an error message, the code just hangs at the
> cutEdges.SetInputConnection(...). The only significant difference as far as
> I can tell is that I'm using an .stl file instead of a .g file. Shouldn't
> the outputport data from vtkSTLReader and vtkBYUReader be the same (a
> vtkAlgorithm object in this case)?
>
> Though I've been using bits and pieces of vtk code over the past year, I'm
> still very unexperienced in VTK (and image processing in general). Am I
> supposed to extract the data from vtkSTLReader in a different way? Any help
> would be greatly appreciated.
>
> Kind regards,
>
> Daniel
>
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