# OrientedCylinder

VTKExamples/Python/GeometricObjects/OrientedCylinder

### Description¶

This example illustrates how to create and display a cylinder 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 True or False.

Compare this example with OrientedArrow. The transform is different because the cylinder height direction is along the y-axis and the arrow height is along the x axis.

Other Languages

See (Cxx), (Java)

Question

### Code¶

OrientedCylinder.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import vtk

'''
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 = True

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

# Set the background color.
colors.SetColor("BkgColor", [26, 51, 77, 255])

# Create a cylinder.
# Cylinder height vector is (0,1,0).
# Cylinder center is in the middle of the cylinder
cylinderSource = vtk.vtkCylinderSource()
cylinderSource.SetResolution(15)

# Generate a random start and end point
startPoint = [0] * 3
endPoint = [0] * 3
rng = vtk.vtkMinimalStandardRandomSequence()
rng.SetSeed(8775070)  # For testing.
for i in range(0, 3):
rng.Next()
startPoint[i] = rng.GetRangeValue(-10, 10)
rng.Next()
endPoint[i] = rng.GetRangeValue(-10, 10)

# Compute a basis
normalizedX = [0] * 3
normalizedY = [0] * 3
normalizedZ = [0] * 3

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

# The Z axis is an arbitrary vector cross X
arbitrary = [0] * 3
for i in range(0, 3):
rng.Next()
arbitrary[i] = rng.GetRangeValue(-10, 10)
vtk.vtkMath.Cross(normalizedX, arbitrary, normalizedZ)
vtk.vtkMath.Normalize(normalizedZ)

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

# Create the direction cosine matrix
matrix.Identity()
for i in range(0, 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)  # translate to starting point
transform.Concatenate(matrix)  # apply direction cosines
transform.RotateZ(-90.0)  # align cylinder to x axis
transform.Scale(1.0, length, 1.0)  # scale along the height vector
transform.Translate(0, .5, 0)  # translate to start of cylinder

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

# Create a mapper and actor for the arrow
mapper = vtk.vtkPolyDataMapper()
actor = vtk.vtkActor()
if USER_MATRIX:
mapper.SetInputConnection(cylinderSource.GetOutputPort())
actor.SetUserMatrix(transform.GetMatrix())
else:
mapper.SetInputConnection(transformPD.GetOutputPort())
actor.SetMapper(mapper)
actor.GetProperty().SetColor(colors.GetColor3d("Cyan"))

# 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(colors.GetColor3d("Yellow"))

sphereEndSource = vtk.vtkSphereSource()
sphereEndSource.SetCenter(endPoint)
sphereEndMapper = vtk.vtkPolyDataMapper()
sphereEndMapper.SetInputConnection(sphereEndSource.GetOutputPort())
sphereEnd = vtk.vtkActor()
sphereEnd.SetMapper(sphereEndMapper)
sphereEnd.GetProperty().SetColor(colors.GetColor3d("Magenta"))

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

# Add the actor to the scene