I also noticed that InterpolateScalarsBeforeMappingOn on works with scalar field , not vector field. In the new code below I set the vector values to the node and activate the correct component by using SelectColorArray and SetArrayComponent, but only field 0 is visualized correctly
import vtk
# Create the 8-node cube (hexahedron)
points = vtk.vtkPoints()
points.InsertNextPoint(0, 0, 0) # Node 0
points.InsertNextPoint(1, 0, 0) # Node 1
points.InsertNextPoint(1, 1, 0) # Node 2
points.InsertNextPoint(0, 1, 0) # Node 3
points.InsertNextPoint(0, 0, 1) # Node 4
points.InsertNextPoint(1, 0, 1) # Node 5
points.InsertNextPoint(1, 1, 1) # Node 6
points.InsertNextPoint(0, 1, 1) # Node 7
# Create the hexahedron (cube) with 8 nodes
# hexahedron = vtk.vtkHexahedron()
hexahedron = vtk.vtkLagrangeHexahedron()
hexahedron.GetPointIds().SetId(0, 0) # Node 0
hexahedron.GetPointIds().SetId(1, 1) # Node 1
hexahedron.GetPointIds().SetId(2, 2) # Node 2
hexahedron.GetPointIds().SetId(3, 3) # Node 3
hexahedron.GetPointIds().SetId(4, 4) # Node 4
hexahedron.GetPointIds().SetId(5, 5) # Node 5
hexahedron.GetPointIds().SetId(6, 6) # Node 6
hexahedron.GetPointIds().SetId(7, 7) # Node 7
# Create an unstructured grid
unstructured_grid = vtk.vtkUnstructuredGrid()
unstructured_grid.SetPoints(points)
unstructured_grid.InsertNextCell(hexahedron.GetCellType(), hexahedron.GetPointIds())
# Create scalar data
pointDataArray = vtk.vtkFloatArray()
pointDataArray.SetName("Nodal_displacements")
pointDataArray.SetNumberOfComponents(3)
pointDataArray.InsertNextTuple3(0.0, 0.0, 0.0) # Node 0
pointDataArray.InsertNextTuple3(0.1, 0.0, 0.0) # Node 1
pointDataArray.InsertNextTuple3(0.1, -0.03, 0.0) # Node 2
pointDataArray.InsertNextTuple3(0.0, -0.03, 0.0) # Node 3
pointDataArray.InsertNextTuple3(0.0, 0.0, -0.03) # Node 4
pointDataArray.InsertNextTuple3(0.1, 0.0, -0.03) # Node 5
pointDataArray.InsertNextTuple3(0.1, -0.03, -0.03) # Node 6
pointDataArray.InsertNextTuple3(0.0, -0.03, -0.03) # Node 7
# Add scalar data to the unstructured grid
unstructured_grid.GetPointData().AddArray(pointDataArray)
# Create a lookup table for the colors
vmin = -0.03
vmax = 0.0
lookup_table = vtk.vtkLookupTable()
lookup_table.SetTableRange(vmin, vmax) # Set vmin and vmax to the scalar range
lookup_table.SetNumberOfColors(256) # Set the number of colors in the table (256 is common)
# lookup_table.SetColorSpaceToDiverging()
lookup_table.Build() # Build the lookup table
# Create a mapper
mapper = vtk.vtkDataSetMapper()
mapper.SetInputData(unstructured_grid)
mapper.ScalarVisibilityOn()
mapper.SetScalarModeToUsePointFieldData()
mapper.SelectColorArray("Nodal_displacements")
mapper.SetArrayComponent(1)
mapper.SetScalarRange(vmin, vmax)
mapper.SetLookupTable(lookup_table)
mapper.InterpolateScalarsBeforeMappingOn() # important to let the cell to interpolate the scalar before doing color mapping
# otherwise the color will be interpolated via vertex value and it will not be accurate
# Ref: https://discourse.vtk.org/t/color-does-not-match-with-values-on-look-up-table/15459
# Create an actor
actor = vtk.vtkActor()
actor.SetMapper(mapper)
# Create a renderer, render window, and interactor
renderer = vtk.vtkRenderer()
renderWindow = vtk.vtkRenderWindow()
renderWindow.AddRenderer(renderer)
renderWindowInteractor = vtk.vtkRenderWindowInteractor()
renderWindowInteractor.SetRenderWindow(renderWindow)
# Add the actor to the renderer
renderer.AddActor(actor)
# Set background color to white
renderer.SetBackground(1.0, 1.0, 1.0)
# Use the scalar bar to display the color range
scalarBar = vtk.vtkScalarBarActor()
scalarBar.SetLookupTable(lookup_table)
# scalarBar.SetTitle("Node Scalars")
scalarBar.SetNumberOfLabels(5)
# Add the scalar bar to the renderer
renderer.AddActor2D(scalarBar)
# # Create an axes actor (this will be used for vtkOrientationMarkerWidget)
# axes = vtk.vtkAxesActor()
# # Create the orientation marker widget
# orientation_marker = vtk.vtkOrientationMarkerWidget()
# orientation_marker.SetOrientationMarker(axes)
# orientation_marker.SetInteractor(renderWindowInteractor)
# orientation_marker.SetViewport(0.0, 0.0, 0.2, 0.2) # Position of the axes in the viewport (relative coordinates)
# orientation_marker.SetEnabled(True) # Enable the widget
# Set the camera position
camera = renderer.GetActiveCamera()
camera.SetPosition(3, 3, 3) # Position the camera at (3, 3, 3)
camera.SetFocalPoint(0.5, 0.5, 0.5) # Set the focal point (where the camera looks)
camera.SetViewUp(0, 1, 0) # Set the view-up direction
# Set the size of the render window
renderWindow.SetSize(600, 600)
# Start the rendering loop
renderWindow.Render()
# style = vtk.vtkInteractorStyleTrackballCamera()
# renderWindowInteractor.SetInteractorStyle(style)
renderWindowInteractor.Start()