# SmoothMeshgrid

VTKExamples/Python/PolyData/SmoothMeshgrid

### Description

Create a terrain with regularly spaced points. The triangles are created manually. Then different types of smoothing filters are used to smooth the terrain.

Left : initial terrain, middle : vtkLoopSubdivisionFilter, right : vtkButterflySubdivisionFilter

*Contributed by Michka Popoff, with the help of Bill Lorensen and madz (madaramh).

### Code

SmoothMeshgrid.py

    #!/usr/bin/env python

    import vtk
    import random
    import numpy

    # Make a 32 x 32 grid
    size = 32

    # Define z values for the topography (random height)
    topography = numpy.zeros([size, size])
    for i in range(size):
        for j in range(size):
            topography[i][j] = random.randrange(0, 5)

    # Define points, triangles and colors
    colors = vtk.vtkUnsignedCharArray()
    colors.SetNumberOfComponents(3)
    points = vtk.vtkPoints()
    triangles = vtk.vtkCellArray()

    # Build the meshgrid manually
    count = 0
    for i in range(size-1):
        for j in range(size-1):

            z1 = topography[i][j]
            z2 = topography[i][j+1]
            z3 = topography[i+1][j]

            # Triangle 1
            points.InsertNextPoint(i, j, z1)
            points.InsertNextPoint(i, (j+1), z2)
            points.InsertNextPoint((i+1), j, z3)

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

            triangles.InsertNextCell(triangle)

            z1 = topography[i][j+1]
            z2 = topography[i+1][j+1]
            z3 = topography[i+1][j]

            # Triangle 2
            points.InsertNextPoint(i, (j+1), z1)
            points.InsertNextPoint((i+1), (j+1), z2)
            points.InsertNextPoint((i+1), j, z3)

            triangle = vtk.vtkTriangle()
            triangle.GetPointIds().SetId(0, count + 3)
            triangle.GetPointIds().SetId(1, count + 4)
            triangle.GetPointIds().SetId(2, count + 5)

            count += 6

            triangles.InsertNextCell(triangle)

            # Add some color
            r = [int(i/float(size)*255),int(j/float(size)*255),0]
            colors.InsertNextTupleValue(r)
            colors.InsertNextTupleValue(r)
            colors.InsertNextTupleValue(r)
            colors.InsertNextTupleValue(r)
            colors.InsertNextTupleValue(r)
            colors.InsertNextTupleValue(r)

    # Create a polydata object
    trianglePolyData = vtk.vtkPolyData()

    # Add the geometry and topology to the polydata
    trianglePolyData.SetPoints(points)
    trianglePolyData.GetPointData().SetScalars(colors)
    trianglePolyData.SetPolys(triangles)

    # Clean the polydata so that the edges are shared !
    cleanPolyData = vtk.vtkCleanPolyData()
    cleanPolyData.SetInputData(trianglePolyData)

    # Use a filter to smooth the data (will add triangles and smooth)
    # Use two different filters to show the difference
    smooth_loop = vtk.vtkLoopSubdivisionFilter()
    smooth_loop.SetNumberOfSubdivisions(3)
    smooth_loop.SetInputConnection(cleanPolyData.GetOutputPort())
    smooth_butterfly = vtk.vtkButterflySubdivisionFilter()
    smooth_butterfly.SetNumberOfSubdivisions(3)
    smooth_butterfly.SetInputConnection(cleanPolyData.GetOutputPort())

    # Create a mapper and actor for initial dataset
    mapper = vtk.vtkPolyDataMapper()
    mapper.SetInputData(trianglePolyData)
    actor = vtk.vtkActor()
    actor.SetMapper(mapper)

    # Create a mapper and actor for smoothed dataset (vtkLoopSubdivisionFilter)
    mapper = vtk.vtkPolyDataMapper()
    mapper.SetInputConnection(smooth_loop.GetOutputPort())
    actor_loop = vtk.vtkActor()
    actor_loop.SetMapper(mapper)
    actor_loop.SetPosition(32, 0, 0)

    # Create a mapper and actor for smoothed dataset (vtkButterflySubdivisionFilter)
    mapper = vtk.vtkPolyDataMapper()
    mapper.SetInputConnection(smooth_butterfly.GetOutputPort())
    actor_butterfly = vtk.vtkActor()
    actor_butterfly.SetMapper(mapper)
    actor_butterfly.SetPosition(64, 0, 0)

    # Visualise
    renderer = vtk.vtkRenderer()
    renderWindow = vtk.vtkRenderWindow()
    renderWindow.AddRenderer(renderer)
    renderWindowInteractor = vtk.vtkRenderWindowInteractor()
    renderWindowInteractor.SetRenderWindow(renderWindow)

    # Add actors and render
    renderer.AddActor(actor)
    renderer.AddActor(actor_loop)
    renderer.AddActor(actor_butterfly)

    renderer.SetBackground(1, 1, 1) # Background color white
    renderWindow.SetSize(800, 800)
    renderWindow.Render()
    renderWindowInteractor.Start()