# 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).

Question

### Code¶

SmoothMeshGrid.py

#!/usr/bin/env python

import numpy
import vtk

def main():
nc = vtk.vtkNamedColors()

# Make a 32 x 32 grid
size = 32

rn = vtk.vtkMinimalStandardRandomSequence()
rn.SetSeed(1)

# 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] = rn.GetRangeValue(0, 5)
rn.Next()

# 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)

r = [int(i / float(size) * 255), int(j / float(size) * 255), 0]
colors.InsertNextTypedTuple(r)
colors.InsertNextTypedTuple(r)
colors.InsertNextTypedTuple(r)
colors.InsertNextTypedTuple(r)
colors.InsertNextTypedTuple(r)
colors.InsertNextTypedTuple(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()
renderWindowInteractor = vtk.vtkRenderWindowInteractor()
renderWindowInteractor.SetRenderWindow(renderWindow)

renderer.SetBackground(nc.GetColor3d("AliceBlue"))

renderWindow.SetSize(900, 300)
renderWindow.Render()
renderer.GetActiveCamera().Elevation(-45)
renderer.GetActiveCamera().Zoom(3)
renderWindow.Render()
renderWindowInteractor.Start()

if __name__ == '__main__':
main()