Inconsistent Render of Colored PolyData

Support
1

Hi,

I have a number of unstructured meshes (of right ventricles) converted to PolyData on which I am attempting to identify physiologically relevant regions (septal wall, free wall, valves, etc). Based on location, curvature, and cell normals, I create a scalar array of cell data that contains integers for each region.

To check the accuracy of my approach, I’ve created a render object to take a PolyData input and write a PNG of the render. I can also write out a vtk file at the same point in the code and visualize the PolyData in Paraview. These yield inconsistent results (Paraview is correct).

Some code snippets (the render object first)

class DebugRender:
    def __init__(self):
        self.mapper = vtkPolyDataMapper()
        self.actor = vtkActor()
        self.actor.SetMapper(self.mapper)

        self.render = vtkRenderer()
        self.render.AddActor(self.actor)

        self.window = vtkRenderWindow()
        self.window.AddRenderer(self.render)
        self.window.OffScreenRenderingOn()
    def set_map_input(self, meshdata):
        self.mapper.SetInputData(meshdata)
        self.mapper.Update()
    def call_render(self):
        self.window.Render()
    def write_render(self, name):
        winfilt = vtkWindowToImageFilter()
        winfilt.SetInput(self.window)
        w = vtkPNGWriter()
        w.SetInputConnection(winfilt.GetOutputPort())
        w.SetFileName(name)
        w.Update()
        w.Write()

and the actual use of this (note g.meshdata is the polydata object and self.regions contains the values I want to visualize):

  g.meshdata.GetCellData().AddArray(self.regions)
  g.meshdata.GetCellData().SetScalars(self.regions)
  db = DebugRender()
  db.set_map_input(g.meshdata)
  db.call_render()
  db.write_render('TestOutput.png')

Again, using the debugger I also wrote out the polydata to a vtk file, and loaded it up into Paraview.

The results are:
(from the render) TestOutput
(viewed in Paraview) ParaviewOutput
The particular problem is that the oval regions (top middle and seen from edge at bottom) are not the right color - the render colors them the same as the left side of the mesh, unlike the correct values shown in the Paraview window.

2

I figured this out myself. I forgot that Paraview transparently does a lot of great stuff, whereas in vtk, you gotta do it all. It is what it is :grin:

First, I took the render process out of a class (I originally had it there because I thought I’d build the pipeline and then use it frequently, but I’m actually only calling it once now). So that code is now:

def DebugRender(meshdata, name):
    """ Render function for debugging regions """
    transf = vtkColorTransferFunction()
    transf.AddRGBPoint(0.0, 0.231373, 0.298039, 0.752941)
    transf.AddRGBPoint(2.5, 0.865003, 0.865003, 0.865003)
    transf.AddRGBPoint(5.0, 0.705882, 0.0155863, 0.14902)
    # I yoinked these values from Paraview's transfer function!
    transf.Build()

    mapper = vtkPolyDataMapper()
    mapper.SetInputData(meshdata)
    mapper.SetLookupTable(transf)
    mapper.Update()

    actor = vtkActor()
    actor.SetMapper(mapper)

    render = vtkRenderer()
    render.AddActor(actor)

    window = vtkRenderWindow()
    window.AddRenderer(render)
    window.OffScreenRenderingOn()
    window.Render()

    winfilt = vtkWindowToImageFilter()
    winfilt.SetInput(window)

    w = vtkPNGWriter()
    w.SetInputConnection(winfilt.GetOutputPort())
    w.SetFileName(name)
    w.Update()
    w.Write()

where the function inputs meshdata and names are a vtkPolyData object and a filename string and the actual call looks like:

    g.meshdata.GetCellData().AddArray(self.regions)
    g.meshdata.GetCellData().SetActiveScalars('Region')
    DebugRender(g.meshdata, names.outimg[0])

where again from before g.meshdata is the vtkPolyData object and self.regions is the vtkDoubleArray I want to visualize on cells. Now I get:
(vtk render)APAH-CHD_02_00-regions
(paraview)Paraview_View
Hope this helps someone in the future…