[vtkusers] Cutting lines where they intersect a sphere?

[James Carroll]

Hi,  I'm trying to find the intersection of lines with a sphere.  I
was hoping that the clipper or the cutter would take an input set of
lines, and as output give just the portions of the lines that are
inside the sphere.  It looks like that's not what they do.

Is there anything in VTK that will cut a line where it intersects a sphere?

I had hopes for the cutter, but I don't get any output with:
lineMapper.SetInput(cutter.GetOutput())

I think it's because the cutter, when cutting lines will produce
points (dimension n-1)
but I need to have cut lines as a result.

My python test code is below.
Thanks,
-Jim



import vtk
from vtk.util.colors import *

math = vtk.vtkMath()

actors = []

# create a rat's nest of lines
points = vtk.vtkPoints()
lines = vtk.vtkCellArray()
lines.InsertNextCell(200)
for i in range(10):
    #points.InsertPoint(i, math.Random(-1, 1), math.Random(-1, 1),
math.Random(-0.2, 0.2))
    ip = (i-5.0) / 5.0
    for j in range(10):
        jp = (j-5.0) / 5.0
        pt = i * j * 2
        points.InsertPoint(pt, -1.0, ip, -jp)
        lines.InsertCellPoint(pt)
        points.InsertPoint(pt+1, 1.0, -ip, jp)
        lines.InsertCellPoint(pt+1)
    #
#

linePolys = vtk.vtkPolyData()
linePolys.SetPoints(points)
linePolys.SetLines(lines)

# clip to the sphere
# a sphere to clip
cutSphere = vtk.vtkSphere()
cutSphere.SetRadius(0.5)

clipper = vtk.vtkClipPolyData()
clipper.SetInput(linePolys)
clipper.SetClipFunction(cutSphere)
#clipper.GenerateClipScalarsOn()
clipper.GenerateClippedOutputOn()
#clipper.GenerateClippedData(True)
#clipper.SetValue(0.5)

cutter = vtk.vtkCutter()
cutter.SetInput(linePolys)
cutter.SetCutFunction(cutSphere)
cutter.GenerateCutScalarsOn()
#cutter.SetValue(1.0, 0.5)

lineMapper = vtk.vtkPolyDataMapper()
#lineMapper.SetInput(linePolys)
#lineMapper.SetInput(clipper.GetOutput())
lineMapper.SetInput(cutter.GetOutput())
lineActor = vtk.vtkActor()
lineActor.SetMapper(lineMapper)
lineActor.GetProperty().SetColor(red)
#lineActor.GetProperty().SetOpacity(0.6)
actors.append(lineActor)

# a sphere to show
sphere = vtk.vtkSphereSource()
sphere.SetRadius(0.5)
sphereMapper = vtk.vtkPolyDataMapper()
sphereMapper.SetInput(sphere.GetOutput())
sphereActor = vtk.vtkActor()
sphereActor.SetMapper(sphereMapper)
sphereActor.GetProperty().SetOpacity(0.05)
actors.append(sphereActor)

# rendering stuff
ren = vtk.vtkRenderer()
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren)
iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)
# Add the actors to the renderer, set the background and size
for actor in actors:
    ren.AddActor(actor)

ren.SetBackground(1, 1, 1)
renWin.SetSize(600, 400)

camera = vtk.vtkCamera()
camera.SetClippingRange(1.81325, 90.6627)
camera.SetFocalPoint(0, 0, 0)
camera.SetPosition(4.5, 1.0, 6.73257)
camera.SetViewUp(0, 1, 0)
camera.Zoom(1.0)
ren.SetActiveCamera(camera)

iren.Initialize()
renWin.Render()
iren.Start()