VTK/Examples/Cxx/SimpleOperations/PerspectiveTransform

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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.

PerspectiveTransform.cxx

#include <vtkSmartPointer.h>
#include <vtkPerspectiveTransform.h>
#include <vtkTransform.h>
#include <vtkMatrix4x4.h>
 
int main(int, char *[])
{
  vtkSmartPointer<vtkMatrix4x4> m =
    vtkSmartPointer<vtkMatrix4x4>::New();
  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);
 
  vtkSmartPointer<vtkPerspectiveTransform> perspectiveTransform = 
      vtkSmartPointer<vtkPerspectiveTransform>::New();
  perspectiveTransform->SetMatrix(m);
 
  vtkSmartPointer<vtkTransform> transform =
      vtkSmartPointer<vtkTransform>::New();
  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 2.8)
 
PROJECT(PerspectiveTransform)
 
find_package(VTK REQUIRED)
include(${VTK_USE_FILE})
 
if (APPLE)
  add_executable(PerspectiveTransform MACOSX_BUNDLE PerspectiveTransform.cxx)
else()
  add_executable(PerspectiveTransform PerspectiveTransform.cxx)
endif()
 
if(VTK_LIBRARIES)
  target_link_libraries(PerspectiveTransform ${VTK_LIBRARIES})
else()
  target_link_libraries(PerspectiveTransform vtkHybrid vtkHybrid)
endif()
Retrieved from "http://www.vtk.org/Wiki/VTK/Examples/Cxx/SimpleOperations/PerspectiveTransform"
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