# Unstructured grid example¶

A MayaVi example of how to generate an unstructured grid dataset using numpy arrays. Also shown is a way to visualize this data with mayavi2. The script can be run like so:

\$ mayavi2 -x unstructured_grid.py

Alternatively, it can be run as:

\$ python unstructured_grid.py

Author: Prabhu Ramachandran <prabhu at aero dot iitb dot ac dot in>

Python source code: `unstructured_grid.py`

```
from numpy import array, arange, random
from tvtk.api import tvtk
from mayavi.scripts import mayavi2

def single_type_ug():
"""Simple example showing how to create an unstructured grid
consisting of cells of a single type.
"""
points = array([[0,0,0], [1,0,0], [0,1,0], [0,0,1], # tets
[1,0,0], [2,0,0], [1,1,0], [1,0,1],
[2,0,0], [3,0,0], [2,1,0], [2,0,1],
], 'f')
tets = array([[0, 1, 2, 3], [4, 5, 6, 7], [8, 9, 10, 11]])
tet_type = tvtk.Tetra().cell_type
ug = tvtk.UnstructuredGrid(points=points)
ug.set_cells(tet_type, tets)
return ug

def mixed_type_ug():
"""A slightly more complex example of how to generate an
unstructured grid with different cell types.  Returns a created
unstructured grid.
"""
points = array([[0,0,0], [1,0,0], [0,1,0], [0,0,1], # tetra
[2,0,0], [3,0,0], [3,1,0], [2,1,0],
[2,0,1], [3,0,1], [3,1,1], [2,1,1], # Hex
], 'f')
# shift the points so we can show both.
points[:,1] += 2.0
# The cells
cells = array([4, 0, 1, 2, 3, # tetra
8, 4, 5, 6, 7, 8, 9, 10, 11 # hex
])
# The offsets for the cells, i.e. the indices where the cells
# start.
offset = array([0, 5])
tetra_type = tvtk.Tetra().cell_type # VTK_TETRA == 10
hex_type = tvtk.Hexahedron().cell_type # VTK_HEXAHEDRON == 12
cell_types = array([tetra_type, hex_type])
# Create the array of cells unambiguously.
cell_array = tvtk.CellArray()
cell_array.set_cells(2, cells)
# Now create the UG.
ug = tvtk.UnstructuredGrid(points=points)
# Now just set the cell types and reuse the ug locations and cells.
ug.set_cells(cell_types, offset, cell_array)
return ug

def save_xml(ug, file_name):
"""Shows how you can save the unstructured grid dataset to a VTK
XML file."""
w = tvtk.XMLUnstructuredGridWriter(input=ug, file_name=file_name)
w.write()

# ----------------------------------------------------------------------
# Create the unstructured grids and assign scalars and vectors.
ug1 = single_type_ug()
ug2 = mixed_type_ug()
temperature = arange(0, 120, 10, 'd')
velocity = random.randn(12, 3)
for ug in ug1, ug2:
ug.point_data.scalars = temperature
ug.point_data.scalars.name = 'temperature'
# Some vectors.
ug.point_data.vectors = velocity
ug.point_data.vectors.name = 'velocity'

# Uncomment this to save the file to a VTK XML file.
#save_xml(ug2, 'file.vtu')

# Now view the data.
@mayavi2.standalone
def view():
from mayavi.sources.vtk_data_source import VTKDataSource
from mayavi.modules.outline import Outline
from mayavi.modules.surface import Surface
from mayavi.modules.vectors import Vectors

mayavi.new_scene()
# The single type one
src = VTKDataSource(data = ug1)