VTK/Examples/Python/Visualization/ClampGlyphSizes

ClampGlyphSizes.py

# Example of how to use range clamping with vtkGlyph3D filter.
#
# Note that the internal algorithm does this to figure out the eventual scale
# of your data (say, if you're scaling by a scalar or vector magnitude):
#
# 	scale = (scalar value of that particular data index);
# 	denominator = Range[1] - Range[0];
# 	scale = (scale < Range[0] ? Range[0] : (scale > Range[1] ? Range[1] : scale));
# 	scale = (scale - Range[0]) / denominator;
# 	scale *= scaleFactor;
#
# So, step 4 is the unintuitive one. Say your data varies from [0, 1] and you set the
# Range to [0.5, 1]. Everything below 0.5 will be mapped to 0. If you want to set a
# minimum size to your glyphs, then you can set the Range as something like [-0.5, 1]


import vtk

# Generate an image data set with multiple attribute arrays to probe and view
# We will glyph these points with cones and scale/orient/color them with the 
# various attributes

# The Wavelet Source is nice for generating a test vtkImageData set
rt = vtk.vtkRTAnalyticSource()
rt.SetWholeExtent(-2,2,-2,2,0,0)

# Take the gradient of the only scalar 'RTData' to get a vector attribute
grad = vtk.vtkImageGradient()
grad.SetDimensionality(3)
grad.SetInputConnection(rt.GetOutputPort())

# Elevation just to generate another scalar attribute that varies nicely over the data range
elev = vtk.vtkElevationFilter()
# Elevation values will range from 0 to 1 between the Low and High Points
elev.SetLowPoint(-2,0,0)
elev.SetHighPoint(2,0,0)
elev.SetInputConnection(grad.GetOutputPort())

# Generate the cone for the glyphs
sph = vtk.vtkConeSource()
sph.SetRadius(0.1)
sph.SetHeight(0.5)

# Set up the glyph filter
glyph = vtk.vtkGlyph3D()
glyph.SetInputConnection(elev.GetOutputPort())
glyph.SetSourceConnection(sph.GetOutputPort())
glyph.ScalingOn()
glyph.SetScaleModeToScaleByScalar()
glyph.SetVectorModeToUseVector()
glyph.OrientOn()

# Tell the filter to "clamp" the scalar range
glyph.ClampingOn()  

# Set the overall (multiplicative) scaling factor
glyph.SetScaleFactor(1)

# Set the Range to "clamp" the data to 
#   -- see equations above for nonintuitive definition of "clamping"
# The fact that I'm setting the minimum value of the range below
#   the minimum of my data (real min=0.0) with the equations above
#   forces a minimum non-zero glyph size.

glyph.SetRange(-0.5, 1)    # Change these values to see effect on cone sizes

# Tell glyph which attribute arrays to use for what
glyph.SetInputArrayToProcess(0,0,0,0,'Elevation')		# scalars
glyph.SetInputArrayToProcess(1,0,0,0,'RTDataGradient')		# vectors
# glyph.SetInputArrayToProcess(2,0,0,0,'nothing')		# normals
glyph.SetInputArrayToProcess(3,0,0,0,'RTData')		# colors

# Calling update because I'm going to use the scalar range to set the color map range
glyph.Update()

coloring_by = 'RTData'
mapper = vtk.vtkPolyDataMapper()
mapper.SetInputConnection(glyph.GetOutputPort())
mapper.SetScalarModeToUsePointFieldData()
mapper.SetColorModeToMapScalars()
mapper.ScalarVisibilityOn()
mapper.SetScalarRange(glyph.GetOutputDataObject(0).GetPointData().GetArray(coloring_by).GetRange())
mapper.SelectColorArray(coloring_by)
actor = vtk.vtkActor()
actor.SetMapper(mapper)

ren = vtk.vtkRenderer()
ren.AddActor(actor)
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren)
iren = vtk.vtkRenderWindowInteractor()
istyle = vtk.vtkInteractorStyleTrackballCamera()
iren.SetInteractorStyle(istyle)
iren.SetRenderWindow(renWin)
ren.ResetCamera()
renWin.Render()

iren.Start()