VTK displaying finite element mesh using vtkunstructuredgrid from data file of coordinates

Hi guys,

Just wanted to show you my current working code. I am displaying a finite element mesh, using a vtkunstructuredgrid. The data consists of data points starting from 1, their coordinates, as well as connectivity info, that is, how the points connect to form cells/ elements.

Here it is below:

#!/usr/bin/env python

# Author: Helvin Lui

# This is a function, which takes a string parameter: file_path. This string is

# the path of the geometry txt file from which vtk will grab and display data.

def displayMesh(file_path):

import vtk

from vtk import vtkTriangle, vtkQuad

VTK_TRIANGLE = vtkTriangle().GetCellType()

VTK_QUAD = vtkQuad().GetCellType()

with open(file_path, 'r') as f:

aMeshGrid = vtk.vtkUnstructuredGrid()

# The numbers in the bracket below does not appear to make a huge difference.

# I read somewhere that its only an estimate of something...

aMeshGrid.Allocate(2, 180)

# Get number of mesh points

no_points = int(f.readline())

# Set number of points

meshPoints = vtk.vtkPoints()

meshPoints.SetNumberOfPoints(no_points)

# Iterate through point data

for i in range(no_points):

# Get coord info for each point

point_info = f.readline().split() # I need to split, before I assign to point_coord

# else the whole thing is split into single numbers

point_ID = (int(point_info[0])-1) # -1 because the IDs need to start with 0.

point_x = float(point_info[1])

point_y = float(point_info[2])

point_z = float(point_info[3])

# Set coord info in mesh

meshPoints.InsertPoint(point_ID, point_x, point_y, point_z)

# Get number of elements

no_elements = int(f.readline())

# Set number of elements

for i in range(no_elements):

element_info = f.readline().split()

element_ID = (int(element_info[0])-1)

element_no_nodes = int(element_info[1])

element_ID_list = vtk.vtkIdList()

for j in range(element_no_nodes):

node_no = int(element_info[j+2])

element_ID_list.InsertNextId(node_no -1)

print j, node_no

if element_no_nodes == 3: # a triangle

cell_type = VTK_TRIANGLE

elif element_no_nodes == 4: # a rectangle/quad

cell_type = VTK_QUAD

aMeshGrid.InsertNextCell(cell_type, element_ID_list)

aMeshGrid.SetPoints(meshPoints)

aMeshMapper = vtk.vtkDataSetMapper()

aMeshMapper.SetInput(aMeshGrid)

aMeshActor = vtk.vtkActor()

aMeshActor.AddPosition(0,0,0)

aMeshActor.SetMapper(aMeshMapper)

aMeshActor.GetProperty().SetDiffuseColor(0, 0.5, 0)

aMeshActor.GetProperty().SetEdgeVisibility(1)

aMeshActor.GetProperty().SetEdgeColor(1, 0, 0)

# Create the usual rendering stuff.

ren = vtk.vtkRenderer()

renWin = vtk.vtkRenderWindow()

renWin.AddRenderer(ren)

renWin.SetSize(300, 300)

iren = vtk.vtkRenderWindowInteractor()

iren.SetRenderWindow(renWin)

ren.AddActor(aMeshActor)

ren.ResetCamera()

cam1 = ren.GetActiveCamera()

## Render the scene and start interaction.

iren.Initialize()

renWin.Render()

iren.Start()

The data file that you might display could look like this:

7

1 1.000000000 0.000000000 0.000000000

2 3.000000000 0.000000000 0.000000000

3 0.000000000 2.000000000 0.000000000

4 2.000000000 2.000000000 0.000000000

5 4.000000000 2.000000000 0.000000000

6 1.000000000 4.000000000 0.000000000

7 3.000000000 4.000000000 0.000000000

6

1 3 1 4 3

2 3 1 2 4

3 3 2 5 4

4 3 3 4 6

5 3 4 7 6

6 3 4 5 7

It is essentially 'the number of points', then a list of point IDs and their coordinates, then 'the number of elements', then a list of point IDs and their shape (no. of sides; in this case, the elements are triangles), and the coordinates.

Note that I was getting problems with the point IDs, because my data file's IDs started with 1. However, vtk numbering starts with 0. So I needed to '-1' (in red font above) whenever I accessed point numbers. So you will need to be careful if your data points start at 1.