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Examples/ImageProcessing/Python/Contours2D.py

 #!/usr/bin/env python
 
+# This example shows how to sample a mathematical function over a
+# volume. A slice from the volume is then extracted and then contoured
+# to produce 2D contour lines.
+#
 import vtk
 
-# Quadric definition
+# Quadric definition. This is a type of implicit function. Here the 
+# coefficients to the equations are set.
 quadric = vtk.vtkQuadric()
 quadric.SetCoefficients(.5, 1, .2, 0, .1, 0, 0, .2, 0, 0)
 
+# The vtkSampleFunction uses the quadric function and evaluates function
+# value over a regular lattice (i.e., a volume).
 sample = vtk.vtkSampleFunction()
 sample.SetSampleDimensions(30, 30, 30)
 sample.SetImplicitFunction(quadric)
 sample.ComputeNormalsOff()
 sample.Update()
 
+# Here a single slice (i.e., image) is extracted from the volume. (Note: in
+# actuality the VOI request causes the sample function to operate on just the
+# slice.)
 extract = vtk.vtkExtractVOI()
 extract.SetInput(sample.GetOutput())
 extract.SetVOI(0, 29, 0, 29, 15, 15)
 extract.SetSampleRate(1, 2, 3)
 
+# The image is contoured to produce contour lines. Thirteen contour values
+# ranging from (0,1.2) inclusive are produced.
 contours = vtk.vtkContourFilter()
 contours.SetInput(extract.GetOutput())
 contours.GenerateValues(13, 0.0, 1.2)
 
+# The contour lines are mapped to the graphics library.
 contMapper = vtk.vtkPolyDataMapper()
 contMapper.SetInput(contours.GetOutput())
 contMapper.SetScalarRange(0.0, 1.2)
@@ -28,7 +41,7 @@ contMapper.SetScalarRange(0.0, 1.2)
 contActor = vtk.vtkActor()
 contActor.SetMapper(contMapper)
 
-# Create outline
+# Create outline an outline of the sampled data.
 outline = vtk.vtkOutlineFilter()
 outline.SetInput(sample.GetOutput())
 
@@ -39,19 +52,23 @@ outlineActor = vtk.vtkActor()
 outlineActor.SetMapper(outlineMapper)
 outlineActor.GetProperty().SetColor(0, 0, 0)
 
-# create graphics objects
+# Create the renderer, render window, and interactor.
 ren = vtk.vtkRenderer()
 renWin = vtk.vtkRenderWindow()
 renWin.AddRenderer(ren)
 iren = vtk.vtkRenderWindowInteractor()
 iren.SetRenderWindow(renWin)
 
+# Set the background color to white. Associate the actors with the
+# renderer.
 ren.SetBackground(1, 1, 1)
 ren.AddActor(contActor)
 ren.AddActor(outlineActor)
 
+# Zoom in a little bit.
 ren.GetActiveCamera().Zoom(1.5)
 
+# Initialize and start the event loop.
 iren.Initialize()
 renWin.Render()
 iren.Start()