Question

I want to display a surface which is textured. I want the triangles boundaries to be visible over the surface in a different color (lets say red). I have found the following code from the vtk code samples but it does not display the triangle boundaries but the filled triangles.

   import vtk

   # create a rendering window and renderer
   ren = vtk.vtkRenderer()
   renWin = vtk.vtkRenderWindow()
   renWin.AddRenderer(ren)

   # create a renderwindowinteractor
   iren = vtk.vtkRenderWindowInteractor()
   iren.SetRenderWindow(renWin)

   # create points
   points = vtk.vtkPoints()
   points.InsertNextPoint(1.0,0.0,0.0)
   points.InsertNextPoint(0.0,0.0,0.0)
   points.InsertNextPoint(0.0,1.0,0.0)

   triangle = vtk.vtkTriangle()
   triangle.GetPointIds().SetId(0,0)
   triangle.GetPointIds().SetId(1,1)
   triangle.GetPointIds().SetId(2,2)

   triangles = vtk.vtkCellArray()
   triangles.InsertNextCell(triangle)

   # polydata object
   trianglePolyData = vtk.vtkPolyData()
   trianglePolyData.SetPoints( points )
   trianglePolyData.SetPolys( triangles )

   # mapper
   mapper = vtk.vtkPolyDataMapper()
   mapper.SetInput(trianglePolyData)

   # actor
   actor = vtk.vtkActor()
   actor.SetMapper(mapper)

   # assign actor to the renderer
   ren.AddActor(actor)

   # enable user interface interactor
   iren.Initialize()
   renWin.Render()
   iren.Start()

Can anybody please let me know that how to display triangle only with the boundaries with a specific color.

I ideally i want to display triangles on a textured surface. My data consist of triangles. It might also be possible that the vertices of the triangles which are given to vtk can be made visible.

I am coding in python.

Thanks a lot

Answer 1

You need to extract the edges from your vtkPolyData object:

edges = vtk.vtkExtractEdges()
edges.SetInput(trianglePolyData)
edge_mapper = vtk.vtkPolyDataMapper()
edge_mapper.SetInput(edges.GetOutput())

edge_actor = vtk.vtkActor()
edge_actor.SetMapper(edge_mapper)
edge_actor.GetProperty().SetColor(1,0,0)

ren.AddActor(edge_actor)

vtk.vtkPolyDataMapper().SetResolveCoincidentTopologyToPolygonOffset()

First you must extract the edges via a vtkExtractEdges filter. You map the results of that filter to a vtkPolyData object and construct an actor for that data. We then set the color of the mesh to red by modifying the actor directly.

The call to vtk.vtkPolyDataMapper().SetResolveCoincidentTopologyToPolygonOffset() prevents the edges from fighting with the surfaces (the two geometric objects are coincident and tear through each other due to z-buffer precision issues).

For completeness sake, here’s the whole code:

import vtk

# create a rendering window and renderer
ren = vtk.vtkRenderer()
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren)

# create a renderwindowinteractor
iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)

# create points
points = vtk.vtkPoints()
points.InsertNextPoint(1.0,0.0,0.0)
points.InsertNextPoint(0.0,0.0,0.0)
points.InsertNextPoint(0.0,1.0,0.0)

triangle = vtk.vtkTriangle()
triangle.GetPointIds().SetId(0,0)
triangle.GetPointIds().SetId(1,1)
triangle.GetPointIds().SetId(2,2)

triangles = vtk.vtkCellArray()
triangles.InsertNextCell(triangle)

# polydata object
trianglePolyData = vtk.vtkPolyData()
trianglePolyData.SetPoints( points )
trianglePolyData.SetPolys( triangles )

# mapper
mapper = vtk.vtkPolyDataMapper()
mapper.SetInput(trianglePolyData)

# actor
actor = vtk.vtkActor()
actor.SetMapper(mapper)

# assign actor to the renderer
ren.AddActor(actor)

#++++++++++++++++++++++++++++++++++++++++++++++++
# Get the edges from the mesh
edges = vtk.vtkExtractEdges()
edges.SetInput(trianglePolyData)
edge_mapper = vtk.vtkPolyDataMapper()
edge_mapper.SetInput(edges.GetOutput())

# Make an actor for those edges    
edge_actor = vtk.vtkActor()
edge_actor.SetMapper(edge_mapper)

# Make the actor red (there are other ways of doing this also)
edge_actor.GetProperty().SetColor(1,0,0)

ren.AddActor(edge_actor)

# Avoid z-buffer fighting
vtk.vtkPolyDataMapper().SetResolveCoincidentTopologyToPolygonOffset()
#------------------------------------------------

# enable user interface interactor
iren.Initialize()
renWin.Render()
iren.Start()