Examples/DataRepresentation/Mesh/PointSetWithVectors.cxx

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//  Software Guide : BeginLatex
//
//  This example illustrates how a point set can be parameterized to manage a
//  particular pixel type. It is quite common to associate vector values with
//  points for producing geometric representations.  The following code shows
//  how vector values can be used as the pixel type on the PointSet class.  The
//  \doxygen{Vector} class is used here as the pixel type. This class is
//  appropriate for representing the relative position between two points. It
//  could then be used to manage displacements, for example.
//
//  \index{itk::PointSet!Vector pixels}
//
//  In order to use the vector class it is necessary to include its header file
//  along with the header of the point set.
//
//  Software Guide : EndLatex

// Software Guide : BeginCodeSnippet
#include "itkVector.h"
#include "itkPointSet.h"
// Software Guide : EndCodeSnippet


int main(int, char *[])
{
  //  Software Guide : BeginLatex
  //
  //  \begin{floatingfigure}[rlp]{6cm}
  //    \centering
  //    \includegraphics[width=4cm]{PointSetWithVectors}
  //    \caption[PointSet with Vectors as PixelType]{Vectors as PixelType.\label{fig:PointSetWithVectors}}
  //  \end{floatingfigure}
  //
  //  The \code{Vector} class is templated over the type used to represent
  //  the spatial coordinates and over the space dimension.  Since the
  //  PixelType is independent of the PointType, we are free to select any
  //  dimension for the vectors to be used as pixel type. However, for the
  //  sake of producing an interesting example, we will use vectors that
  //  represent displacements of the points in the PointSet. Those vectors
  //  are then selected to be of the same dimension as the PointSet.\newline
  //
  //
  //  \index{itk::Vector!itk::PointSet}
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  constexpr unsigned int Dimension = 3;
  using PixelType = itk::Vector< float, Dimension >;
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  Then we use the PixelType (which are actually Vectors) to instantiate the
  //  PointSet type and subsequently create a PointSet object.
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  using PointSetType = itk::PointSet< PixelType, Dimension >;
  PointSetType::Pointer  pointSet = PointSetType::New();
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  The following code is generating a sphere and assigning vector values
  //  to the points. The components of the vectors in this example are
  //  computed to represent the tangents to the circle as shown in
  //  Figure~\ref{fig:PointSetWithVectors}.
  //
  //  \index{itk::PointSet!SetPoint()}
  //  \index{itk::PointSet!SetPointData()}
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  PointSetType::PixelType   tangent;
  PointSetType::PointType   point;

  unsigned int pointId =  0;
  constexpr double radius = 300.0;

  for(unsigned int i=0; i<360; i++)
    {
    const double angle = i * itk::Math::pi / 180.0;
    point[0] = radius * std::sin( angle );
    point[1] = radius * std::cos( angle );
    point[2] = 1.0;   // flat on the Z plane
    tangent[0] =  std::cos(angle);
    tangent[1] = -std::sin(angle);
    tangent[2] = 0.0;  // flat on the Z plane
    pointSet->SetPoint( pointId, point );
    pointSet->SetPointData( pointId, tangent );
    pointId++;
    }
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  We can now visit all the points and use the vector on the pixel values to
  //  apply a displacement on the points. This is along the spirit of what a
  //  deformable model could do at each one of its iterations.
  //
  //  \index{itk::PointSet!PointIterator}
  //  \index{itk::PointSet!GetPoints()}
  //  \index{itk::PointSet!GetPointData()}
  //
  //  Software Guide : EndLatex


  // Software Guide : BeginCodeSnippet
  using PointDataIterator = PointSetType::PointDataContainer::ConstIterator;
  PointDataIterator pixelIterator = pointSet->GetPointData()->Begin();
  PointDataIterator pixelEnd      = pointSet->GetPointData()->End();

  using PointIterator = PointSetType::PointsContainer::Iterator;
  PointIterator pointIterator = pointSet->GetPoints()->Begin();
  PointIterator pointEnd      = pointSet->GetPoints()->End();

  while( pixelIterator != pixelEnd  && pointIterator != pointEnd )
    {
    pointIterator.Value() = pointIterator.Value() + pixelIterator.Value();
    ++pixelIterator;
    ++pointIterator;
    }
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  Note that the \code{ConstIterator} was used here instead of the normal
  //  \code{Iterator} since the pixel values are only intended to be read and
  //  not modified. ITK supports const-correctness at the API level.
  //
  //  \index{ConstIterator}
  //  \index{const-correctness}
  //
  //  Software Guide : EndLatex


  //  Software Guide : BeginLatex
  //
  //  The \doxygen{Vector} class has overloaded the \code{+} operator with
  //  the \doxygen{Point}. In other words, vectors can be added to points in
  //  order to produce new points.  This property is exploited in the center
  //  of the loop in order to update the points positions with a single
  //  statement.
  //
  //  \index{itk::PointSet!PointIterator}
  //
  //  We can finally visit all the points and print out the new values
  //
  //  Software Guide : EndLatex

  // Software Guide : BeginCodeSnippet
  pointIterator = pointSet->GetPoints()->Begin();
  pointEnd      = pointSet->GetPoints()->End();
  while( pointIterator != pointEnd )
    {
    std::cout << pointIterator.Value() << std::endl;
    ++pointIterator;
    }
  // Software Guide : EndCodeSnippet


  //  Software Guide : BeginLatex
  //
  //  Note that \doxygen{Vector} is not the appropriate class for
  //  representing normals to surfaces and gradients of functions. This is due
  //  to the way vectors behave under affine transforms. ITK has a
  //  specific class for representing normals and function gradients. This is
  //  the \doxygen{CovariantVector} class.
  //
  //  Software Guide : EndLatex

  return EXIT_SUCCESS;
}