PerspectiveTransform

Description¶

The perspective transform automatically appends the "homogeneous 1" to the point before it is multiplied by the matrix. It then divides the first 3 coordinates of the result by the 4th coordinate of the result. For comparison, the standard projection (vtkTransform) is also performed with the same matrix and the same point. Note that the results are much different.

Other languages

See (Java), (CSharp)

Question

If you have a question about this example, please use the VTK Discourse Forum

Code¶

PerspectiveTransform.cxx

#include <vtkMatrix4x4.h>
#include <vtkNew.h>
#include <vtkPerspectiveTransform.h>
#include <vtkTransform.h>

int main(int, char*[])
{
  vtkNew<vtkMatrix4x4> m;
  m->SetElement(0, 0, 1);
  m->SetElement(0, 1, 2);
  m->SetElement(0, 2, 3);
  m->SetElement(0, 3, 4);
  m->SetElement(1, 0, 2);
  m->SetElement(1, 1, 2);
  m->SetElement(1, 2, 3);
  m->SetElement(1, 3, 4);
  m->SetElement(2, 0, 3);
  m->SetElement(2, 1, 2);
  m->SetElement(2, 2, 3);
  m->SetElement(2, 3, 4);
  m->SetElement(3, 0, 4);
  m->SetElement(3, 1, 2);
  m->SetElement(3, 2, 3);
  m->SetElement(3, 3, 4);

  vtkNew<vtkPerspectiveTransform> perspectiveTransform;
  perspectiveTransform->SetMatrix(m);

  vtkNew<vtkTransform> transform;
  transform->SetMatrix(m);

  double p[3];
  p[0] = 1.0;
  p[1] = 2.0;
  p[2] = 3.0;

  double normalProjection[3];
  transform->TransformPoint(p, normalProjection);

  std::cout << "Standard projection: " << normalProjection[0] << " "
            << normalProjection[1] << " " << normalProjection[2] << std::endl;

  double perspectiveProjection[3];
  perspectiveTransform->TransformPoint(p, perspectiveProjection);
  std::cout << "Perspective projection: " << perspectiveProjection[0] << " "
            << perspectiveProjection[1] << " " << perspectiveProjection[2]
            << std::endl;

  return EXIT_SUCCESS;
}

CMakeLists.txt¶

cmake_minimum_required(VERSION 3.12 FATAL_ERROR)

project(PerspectiveTransform)

find_package(VTK COMPONENTS 
  CommonCore
  CommonMath
  CommonTransforms
)

if (NOT VTK_FOUND)
  message(FATAL_ERROR "PerspectiveTransform: Unable to find the VTK build folder.")
endif()

# Prevent a "command line is too long" failure in Windows.
set(CMAKE_NINJA_FORCE_RESPONSE_FILE "ON" CACHE BOOL "Force Ninja to use response files.")
add_executable(PerspectiveTransform MACOSX_BUNDLE PerspectiveTransform.cxx )
  target_link_libraries(PerspectiveTransform PRIVATE ${VTK_LIBRARIES}
)
# vtk_module_autoinit is needed
vtk_module_autoinit(
  TARGETS PerspectiveTransform
  MODULES ${VTK_LIBRARIES}
)

Download and Build PerspectiveTransform¶

Click here to download PerspectiveTransform and its CMakeLists.txt file. Once the tarball PerspectiveTransform.tar has been downloaded and extracted,

cd PerspectiveTransform/build

If VTK is installed:

cmake ..

If VTK is not installed but compiled on your system, you will need to specify the path to your VTK build:

cmake -DVTK_DIR:PATH=/home/me/vtk_build ..

Build the project:

make

and run it:

./PerspectiveTransform

WINDOWS USERS

Be sure to add the VTK bin directory to your path. This will resolve the VTK dll's at run time.