ITK  5.3.0
Insight Toolkit
Examples/DataRepresentation/Mesh/Mesh3.cxx
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*
* Copyright NumFOCUS
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* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
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*
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// Software Guide : BeginLatex
//
// Just as custom data can be associated with points in the mesh,
// it is also possible to associate custom data with cells. The type of the
// data associated with the cells can be different from the data type
// associated with points. By default, however, these two types are the same.
// The following example illustrates how to access data associated with
// cells. The approach is analogous to the one used to access point data.
//
// \index{itk::Mesh!Cell data}
//
// Software Guide : EndLatex
// Software Guide : BeginLatex
//
// Consider the example of a mesh containing lines on which values are
// associated with each line. The mesh and cell header files should be
// included first.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
#include "itkMesh.h"
#include "itkLineCell.h"
// Software Guide : EndCodeSnippet
int
main(int, char *[])
{
// Software Guide : BeginLatex
//
// Then the \code{PixelType} is defined and the mesh type is
// instantiated with it.
//
// \index{itk::Mesh!Instantiation}
// \index{itk::Mesh!PixelType}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
using PixelType = float;
using MeshType = itk::Mesh<PixelType, 2>;
// 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 a Mesh and insert some points into 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. We add the \code{vnl\_math::eps} value in order to avoid
// numerical errors when the point id is zero. The value of
// \code{vnl\_math::eps} is the difference between 1.0 and the least value
// greater than 1.0 that is representable in this computer.
//
// \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] = static_cast<PointType::ValueType>(id); // x
point[1] = std::log(static_cast<double>(id) + itk::Math::eps); // y
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.
//
// \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 \doxygen{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 simple example, the square of the cell
// identifier is used as cell data. Note the use of \code{static\_cast} to
// \code{PixelType} in the assignment.
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
for (unsigned int cellId = 0; cellId < numberOfCells; ++cellId)
{
mesh->SetCellData(cellId, static_cast<PixelType>(cellId * cellId));
}
// 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)
{
auto value = static_cast<PixelType>(0.0);
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. More efficient access to cell data can be achieved
// by using the Iterators 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 exactly the same already illustrated
// for getting access to 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 to get the
// value associated with the data entry. \code{PixelType} elements are
// copied into the local variable \code{cellValue}.
//
// \index{CellDataIterator!Value()}
// \index{CellDataIterator!increment}
//
// Software Guide : EndLatex
// Software Guide : BeginCodeSnippet
while (cellDataIterator != end)
{
PixelType cellValue = cellDataIterator.Value();
std::cout << cellValue << std::endl;
++cellDataIterator;
}
// Software Guide : EndCodeSnippet
return EXIT_SUCCESS;
}
itk::GTest::TypedefsAndConstructors::Dimension2::PointType
ImageBaseType::PointType PointType
Definition: itkGTestTypedefsAndConstructors.h:51
itkLineCell.h
itk::Math::eps
static constexpr double eps
Definition: itkMath.h:95
itkMesh.h
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