# VTK/Examples/Python/GeometricObjects/Display/OrientedArrow

< VTK‎ | Examples‎ | Python

This example illustrates how to create and display an arrow that passes through two points.

It demonstrates two different ways to apply the transform:

1. Use vtkTransformPolyDataFilter to create a new transformed polydata. This method is useful if the transformed polydata is needed later in the pipeline, e.g. vtkGlyph3DFilter.
2. Apply the transform directly to the actor using vtkProp3D's SetUserMatrix. No new data is produced.

Switch between the two methods by setting USER_MATRIX to either ${\displaystyle True}$ or ${\displaystyle False}$ as documented in the script.

## OrientedArrow.py

```#!/usr/bin/env python

import vtk
import random

'''
There are two alternative ways to apply the transform.
1) Use vtkTransformPolyDataFilter to create a new transformed polydata.
This method is useful if the transformed polydata is needed
later in the pipeline
To do this, set USER_MATRIX = True
2) Apply the transform directly to the actor using vtkProp3D's SetUserMatrix.
No new data is produced.
To do this, set USER_MATRIX = False
'''
USER_MATRIX = False

#Create an arrow.
arrowSource = vtk.vtkArrowSource()

# Generate a random start and end point
random.seed(8775070)
startPoint = [0 for i in range(3)]
startPoint[0] = random.uniform(-10,10)
startPoint[1] = random.uniform(-10,10)
startPoint[2] = random.uniform(-10,10)
endPoint = [0 for i in range(3)]
endPoint[0] = random.uniform(-10,10)
endPoint[1] = random.uniform(-10,10)
endPoint[2] = random.uniform(-10,10)

# Compute a basis
normalizedX = [0 for i in range(3)]
normalizedY = [0 for i in range(3)]
normalizedZ = [0 for i in range(3)]

# The X axis is a vector from start to end
math = vtk.vtkMath()
math.Subtract(endPoint, startPoint, normalizedX)
length = math.Norm(normalizedX)
math.Normalize(normalizedX)

# The Z axis is an arbitrary vector cross X
arbitrary = [0 for i in range(3)]
arbitrary[0] = random.uniform(-10,10)
arbitrary[1] = random.uniform(-10,10)
arbitrary[2] = random.uniform(-10,10)
math.Cross(normalizedX, arbitrary, normalizedZ)
math.Normalize(normalizedZ)

# The Y axis is Z cross X
math.Cross(normalizedZ, normalizedX, normalizedY)
matrix = vtk.vtkMatrix4x4()

# Create the direction cosine matrix
matrix.Identity()
for i in range(3):
matrix.SetElement(i, 0, normalizedX[i])
matrix.SetElement(i, 1, normalizedY[i])
matrix.SetElement(i, 2, normalizedZ[i])

# Apply the transforms
transform = vtk.vtkTransform()
transform.Translate(startPoint)
transform.Concatenate(matrix)
transform.Scale(length, length, length)

# Transform the polydata
transformPD = vtk.vtkTransformPolyDataFilter()
transformPD.SetTransform(transform)
transformPD.SetInputConnection(arrowSource.GetOutputPort())

#Create a mapper and actor for the arrow
mapper = vtk.vtkPolyDataMapper()
actor = vtk.vtkActor()

if USER_MATRIX:
mapper.SetInputConnection(arrowSource.GetOutputPort())
actor.SetUserMatrix(transform.GetMatrix())
else:
mapper.SetInputConnection(transformPD.GetOutputPort())

actor.SetMapper(mapper)

# Create spheres for start and end point
sphereStartSource = vtk.vtkSphereSource()
sphereStartSource.SetCenter(startPoint)
sphereStartMapper = vtk.vtkPolyDataMapper()
sphereStartMapper.SetInputConnection(sphereStartSource.GetOutputPort())
sphereStart = vtk.vtkActor()
sphereStart.SetMapper(sphereStartMapper)
sphereStart.GetProperty().SetColor(1.0, 1.0, .3)

sphereEndSource = vtk.vtkSphereSource()
sphereEndSource.SetCenter(endPoint)
sphereEndMapper = vtk.vtkPolyDataMapper()
sphereEndMapper.SetInputConnection(sphereEndSource.GetOutputPort())
sphereEnd = vtk.vtkActor()
sphereEnd.SetMapper(sphereEndMapper)
sphereEnd.GetProperty().SetColor(1.0, .3, .3)

#Create a renderer, render window, and interactor
renderer = vtk.vtkRenderer()
renderWindow = vtk.vtkRenderWindow()
renderWindowInteractor = vtk.vtkRenderWindowInteractor()
renderWindowInteractor.SetRenderWindow(renderWindow)

#Add the actor to the scene