ITK  5.3.0
Insight Toolkit
Examples/DataRepresentation/Mesh/MeshTraits.cxx
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// Software Guide : BeginLatex
//
// This section illustrates the full power of
// \href{http://www.boost.org/more/generic_programming.html}{Generic
// Programming}. This is sometimes perceived as \emph{too much of a good
// thing}!
//
// The toolkit has been designed to offer flexibility while keeping the
// complexity of the code to a moderate level. This is achieved in the Mesh
// by hiding most of its parameters and defining reasonable defaults for
// them.
//
// The generic concept of a mesh integrates many different elements. It is
// possible in principle to use independent types for every one of such
// elements. The mechanism used in generic programming for specifying the
// many different types involved in a concept is called \emph{traits}. They
// are basically the list of all types that interact with the current class.
//
// The \doxygen{Mesh} is templated over three parameters. So far only two of
// them have been discussed, namely the \code{PixelType} and the
// \code{Dimension}. The third parameter is a class providing the set of
// traits required by the mesh. When the third parameter is omitted a default
// class is used. This default class is the
// \doxygen{DefaultStaticMeshTraits}. If you want to customize the types used
// by the mesh, the way to proceed is to modify the default traits and
// provide them as the third parameter of the Mesh class instantiation.
//
// There are two ways of achieving this. The first is to use the existing
// \doxygen{DefaultStaticMeshTraits} class. This class is itself templated
// over six parameters. Customizing those parameters could provide enough
// flexibility to define a very specific kind of mesh. The second way is to
// write a traits class from scratch, in which case the easiest way to
// proceed is to copy the \code{DefaultStaticMeshTraits} into another file
// and edit its content. Only the first approach is illustrated here. The
// second is discouraged unless you are familiar with Generic Programming,
// feel comfortable with C++ templates, and have access to an abundant supply
// of (Columbian) coffee.
//
// The first step in customizing the mesh is to include the header file of
// the Mesh and its static traits.
//
// \index{itk::DefaultStaticMeshTraits!Header}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
#include "itkMesh.h"
// Software Guide : EndCodeSnippet
#include "itkLineCell.h"
#include "itkVector.h"
#include "itkMatrix.h"
int
main(int, char *[])
{
// Software Guide : BeginLatex
//
// Then the MeshTraits class is instantiated by selecting the types of each
// one of its six template arguments. They are in order
//
// \begin{description}
// \item[PixelType.] The value type associated with every point.
// \item[PointDimension.] The dimension of the space in which the mesh is
// embedded. \item[MaxTopologicalDimension.] The highest dimension of the
// mesh cells. \item[CoordRepType.] The type used to represent spacial
// coordinates. \item[InterpolationWeightType.] The type used to represent
// interpolation weights. \item[CellPixelType.] The value type associated
// with every cell. \end{description}
//
// Let's define types and values for each one of those elements. For
// example, the following code uses points in 3D space as nodes of the
// Mesh. The maximum dimension of the cells will be two, meaning
// that this is a 2D manifold better know as a \emph{surface}. The data
// type associated with points is defined to be a four-dimensional vector.
// This type could represent values of membership for a four-class
// segmentation method. The value selected for the cells are $4\times3$
// matrices, which could have for example the derivative of the membership
// values with respect to coordinates in space. Finally, a \code{double}
// type is selected for representing space coordinates on the mesh points
// and also for the weight used for interpolating values.
//
// \index{itk::DefaultStaticMeshTraits!Instantiation}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
constexpr unsigned int PointDimension = 3;
constexpr unsigned int MaxTopologicalDimension = 2;
using PixelType = itk::Vector<double, 4>;
using CellDataType = itk::Matrix<double, 4, 3>;
using CoordinateType = double;
using InterpolationWeightType = double;
using MeshTraits = itk::DefaultStaticMeshTraits<PixelType,
PointDimension,
MaxTopologicalDimension,
CoordinateType,
InterpolationWeightType,
CellDataType>;
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// The \doxygen{LineCell} type can now be instantiated using the traits
// taken from the Mesh.
//
// \index{itk::LineCell!Instantiation}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
using CellType = MeshType::CellType;
using LineType = itk::LineCell<CellType>;
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// Let's now create an Mesh and insert some points on it. Note
// that the dimension of the points matches the dimension of the Mesh. Here
// we insert a sequence of points that look like a plot of the $log()$
// function.
//
// \index{itk::Mesh!New()}
// \index{itk::Mesh!SetPoint()}
// \index{itk::Mesh!PointType}
// \index{itk::Mesh!Pointer}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
MeshType::Pointer mesh = MeshType::New();
PointType point;
constexpr unsigned int numberOfPoints = 10;
for (unsigned int id = 0; id < numberOfPoints; ++id)
{
point[0] = 1.565; // Initialize points here
point[1] = 3.647; // with arbitrary values
point[2] = 4.129;
mesh->SetPoint(id, point);
}
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// A set of line cells is created and associated with the existing points
// by using point identifiers. In this simple case, the point identifiers
// can be deduced from cell identifiers since the line cells are ordered in
// the same way. Note that in the code above, the values assigned to point
// components are arbitrary. In a more realistic example, those values
// would be computed from another source.
//
// \index{itk::AutoPointer!TakeOwnership()}
// \index{CellAutoPointer!TakeOwnership()}
// \index{CellType!creation}
// \index{itk::Mesh!SetCell()}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
CellType::CellAutoPointer line;
const unsigned int numberOfCells = numberOfPoints - 1;
for (unsigned int cellId = 0; cellId < numberOfCells; ++cellId)
{
line.TakeOwnership(new LineType);
line->SetPointId(0, cellId); // first point
line->SetPointId(1, cellId + 1); // second point
mesh->SetCell(cellId, line); // insert the cell
}
// Software Guide : EndCodeSnippet
std::cout << "Points = " << mesh->GetNumberOfPoints() << std::endl;
std::cout << "Cells = " << mesh->GetNumberOfCells() << std::endl;
// Software Guide : BeginLatex
//
// Data associated with cells is inserted in the Mesh by using the
// \code{SetCellData()} method. It requires the user to provide an
// identifier and the value to be inserted. The identifier should match one
// of the inserted cells. In this example, we simply store a
// \code{CellDataType} dummy variable named \code{value}.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
for (unsigned int cellId = 0; cellId < numberOfCells; ++cellId)
{
CellDataType value;
mesh->SetCellData(cellId, value);
}
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// Cell data can be read from the Mesh with the
// \code{GetCellData()} method. It requires the user to provide the
// identifier of the cell for which the data is to be retrieved. The user
// should provide also a valid pointer to a location where the data can be
// copied.
//
// \index{itk::Mesh!GetCellData()}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
for (unsigned int cellId = 0; cellId < numberOfCells; ++cellId)
{
CellDataType value;
mesh->GetCellData(cellId, &value);
std::cout << "Cell " << cellId << " = " << value << std::endl;
}
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// Neither \code{SetCellData()} or \code{GetCellData()} are efficient ways
// to access cell data. Efficient access to cell data can be achieved
// by using the \code{Iterator}s built into the \code{CellDataContainer}.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
using CellDataIterator = MeshType::CellDataContainer::ConstIterator;
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// Note that the \code{ConstIterator} is used here because the data is only
// going to be read. This approach is identical to that already
// illustrated for accessing point data. The iterator to the first cell
// data item can be obtained with the \code{Begin()} method of the
// \code{CellDataContainer}. The past-end iterator is returned by the
// \code{End()} method. The cell data container itself can be obtained from
// the mesh with the method \code{GetCellData()}.
//
// \index{itk::Mesh!Iterating cell data}
// \index{itk::Mesh!GetCellData()}
// \index{CellDataContainer!Begin()}
// \index{CellDataContainer!End()}
// \index{CellDataContainer!Iterator}
// \index{CellDataContainer!ConstIterator}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
CellDataIterator cellDataIterator = mesh->GetCellData()->Begin();
CellDataIterator end = mesh->GetCellData()->End();
// Software Guide : EndCodeSnippet
// Software Guide : BeginLatex
//
// Finally a standard loop is used to iterate over all the cell data
// entries. Note the use of the \code{Value()} method used to get the
// actual value of the data entry. \code{PixelType} elements are returned
// by copy.
//
// \index{CellDataIterator!Value()}
// \index{CellDataIterator!increment}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
while (cellDataIterator != end)
{
CellDataType cellValue = cellDataIterator.Value();
std::cout << cellValue << std::endl;
++cellDataIterator;
}
// Software Guide : EndCodeSnippet
return EXIT_SUCCESS;
}
itk::DefaultStaticMeshTraits
Definition: itkDefaultStaticMeshTraits.h:61
itkMatrix.h
itk::GTest::TypedefsAndConstructors::Dimension2::PointType
ImageBaseType::PointType PointType
Definition: itkGTestTypedefsAndConstructors.h:51
itk::Vector
A templated class holding a n-Dimensional vector.
Definition: itkVector.h:62
itkLineCell.h
itkMesh.h
itk::Matrix
A templated class holding a M x N size Matrix.
Definition: itkMatrix.h:51
itk::LineCell
Represents a line segment for a Mesh.
Definition: itkLineCell.h:42
itk::Mesh
Implements the N-dimensional mesh structure.
Definition: itkMesh.h:114
itkDefaultStaticMeshTraits.h
itkVector.h