Simple script showing how to set size and color of glyphs using different scalar arrays

vtk_size_color.py

# vtk_size_color.py --- 
# Author: Subhasis Ray
# Created: Thu Aug  9 11:04:16 2018 (-0400)
# Last-Updated: Thu Aug  9 14:24:15 2018 (-0400)
#           By: Subhasis Ray
# Version: $Id$

# Code:
"""Test simultaneous radius and color settings in glyph.

The key conceptual clarification came from VTK mailing list:

 According to https://www.vtk.org/pipermail/vtkusers/2004-August/026366.html
 
 * Create a sub-class of vtkDataArray for each scalar you have
 * (optional) Assign them names with SetName()
 * Add them to point or cell data with AddArray:
 output->GetPointData()->AddArray(array)
 * Set one of them to be the default scalars:
 output->GetPointData()->SetActiveScalars(array_name)
 Alternatively, you can add the default scalars with
 output->GetPointData()->SetScalars() 
 which internally (sort of) does the following:
 output->GetPointData()->AddArray(array)
 output->GetPointData()->SetActiveScalars(array)

 To later set the default scalars in a VTK pipeline, use
 vtkAssignAttribute. To set which scalar to color by, use
 one of the methods in the mapper:
 SetScalarModeToXXX()
 ColorByComponent()
 SelectColorArray()

"""
import vtk

ctf = vtk.vtkColorTransferFunction()
ctf.AddRGBPoint(0.0, 1.0, 0, 0)
ctf.AddRGBPoint(0.5, 0.0, 1.0, 0)
ctf.AddRGBPoint(1, 0.0, 0, 1.0)

sphere = vtk.vtkSphereSource()
polydata = vtk.vtkPolyData()
points = vtk.vtkPoints()
points.SetNumberOfPoints(2)
points.SetPoint(0, [0, 0, 0])
points.SetPoint(1, [1, 1, 0])
polydata.SetPoints(points)
radii = vtk.vtkFloatArray()
radii.SetName('Radius')
for ii in range(2):
    r = (2 - ii)/2.0
    radii.InsertNextTuple1(r)
    print('Radius {} = {}'.format(ii, r))
polydata.GetPointData().AddArray(radii)
# The following sets the "ActiveScalar", i.e. default scalar used by
# VTK (and is must for setting radius of each sphere by corresponding
# value in radii array). But what tells VTK to use it for scaling?
polydata.GetPointData().SetActiveScalars(radii.GetName())

colors = vtk.vtkFloatArray()
colors.SetName('Color')
for ii in range(2):
    cval = ii/2.0
    colors.InsertNextTuple1(cval)
    print('Color {} = {}, r:{}, g:{}, b:{}'.format(ii, cval,
                                                   ctf.GetRedValue(cval),
                                                   ctf.GetGreenValue(cval),
                                                   ctf.GetBlueValue(cval)))
print('colors array name:', colors.GetName())
polydata.GetPointData().AddArray(colors)
glyph = vtk.vtkGlyph3D()
glyph.SetSourceConnection(sphere.GetOutputPort())
glyph.SetInputData(polydata)
# print('Scale mode:', glyph.GetScaleMode())   # prints 0, default
glyph.SetScaleModeToScaleByScalar()            # Works fine without this! - because this is default
print('Scale mode:', glyph.GetScaleMode())     # prints 0, default
# glyph.SetScaleModeToDataScalingOff()
# print('Scale mode:', glyph.GetScaleMode())  # This prints 3 and the spheres are same radius

mapper = vtk.vtkPolyDataMapper()
mapper.SetInputConnection(glyph.GetOutputPort())
# Right!
# This is the correct way of setting color by the color array attached
# to the pointdata
mapper.SetScalarModeToUsePointFieldData()
# Wrong!
# The following will use radii for color look up
# So 0-th sphere will be blue (r=1.0, blue in CTF)
# and 1st sphere will be green (r=0.5, green in CTF)
# mapper.SetScalarModeToUsePointData()


# mapper.ScalarVisibilityOn()  # Is this required? No.
mapper.SelectColorArray(colors.GetName())
mapper.SetLookupTable(ctf)
actor = vtk.vtkActor()
actor.SetMapper(mapper)
renderer = vtk.vtkRenderer()
renderer.AddActor(actor)
win = vtk.vtkRenderWindow()
win.AddRenderer(renderer)
interactor = vtk.vtkRenderWindowInteractor()
interactor.SetRenderWindow(win)
interactor.Initialize()
interactor.Start()


# 
# vtk_size_color.py ends here