Example source code (Image4.cxx):

 * Copyright (C) 1999-2011 Insight Software Consortium
 * Copyright (C) 2005-2019 Centre National d'Etudes Spatiales (CNES)
 * This file is part of Orfeo Toolbox
 * 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
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * See the License for the specific language governing permissions and
 * limitations under the License.

// Even though OTB can be used to perform
// general image processing tasks, the primary purpose of the toolkit is the
// processing of remote sensing image data.  In that respect, additional
// information about the images is considered mandatory. In particular the
// information associated with the physical spacing between pixels and the
// position of the image in space with respect to some world coordinate
// system are extremely important.
// Image origin and spacing are fundamental to many
// applications. Registration, for example, is performed in physical
// coordinates. Improperly defined spacing and origins will result in
// inconsistent results in such processes. Remote sensing images with no spatial
// information should not be used for image analysis,
// feature extraction, GIS input, etc. In
// other words, remote sensing images lacking spatial information are not only
// useless but also hazardous.
// \begin{figure} \center
// \includegraphics[width=\textwidth]{ImageOriginAndSpacing.eps}
// \itkcaption[OTB Image Geometrical Concepts]{Geometrical concepts associated
// with the OTB image.}
// \label{fig:ImageOriginAndSpacing}
// \end{figure}
// Figure \ref{fig:ImageOriginAndSpacing} illustrates the main geometrical
// concepts associated with the \doxygen{otb}{Image}. In this figure,
// circles are
// used to represent the center of pixels. The value of the pixel is assumed
// to exist as a Dirac Delta Function located at the pixel center. Pixel
// spacing is measured between the pixel centers and can be different along
// each dimension. The image origin is associated with the coordinates of the
// first pixel in the image. A \emph{pixel} is considered to be the
// rectangular region surrounding the pixel center holding the data
// value. This can be viewed as the Voronoi region of the image grid, as
// illustrated in the right side of the figure.  Linear interpolation of
// image values is performed inside the Delaunay region whose corners
// are pixel centers.

#include "otbImage.h"
#include "itkPoint.h"

int main(int, char* [])
  using ImageType = otb::Image<unsigned short, 2>;

  ImageType::Pointer image = ImageType::New();

  ImageType::IndexType start;
  ImageType::SizeType  size;

  size[0] = 200; // size along X
  size[1] = 200; // size along Y

  start[0] = 0; // first index on X
  start[1] = 0; // first index on Y

  ImageType::RegionType region;



  // Image spacing is represented in a \code{FixedArray}
  // whose size matches the dimension of the image. In order to manually set
  // the spacing of the image, an array of the corresponding type must be
  // created.  The elements of the array should then be initialized with the
  // spacing between the centers of adjacent pixels. The following code
  // illustrates the methods available in the Image class for dealing with
  // spacing and origin.
  // \index{otb::Image!Spacing}

  ImageType::SpacingType spacing;

  // Note: measurement units (e.g., meters, feet, etc.) are defined by the application.
  spacing[0] = 0.70; // spacing along X
  spacing[1] = 0.70; // spacing along Y

  // The array can be assigned to the image using
  // the \code{SetSignedSpacing()} method.
  // \index{otb::Image!SetSignedSpacing()}


  // The spacing information can be retrieved from an image by using the
  // \code{GetSignedSpacing()} method. This method returns a reference to a
  // \code{FixedArray}. The returned object can then be used to read the
  // contents of the array. Note the use of the \code{const} keyword to indicate
  // that the array will not be modified.

  const ImageType::SpacingType& sp = image->GetSignedSpacing();

  std::cout << "Spacing = ";
  std::cout << sp[0] << ", " << sp[1] << std::endl;

  // The image origin is managed in a similar way to the spacing.  A
  // \code{Point} of the appropriate dimension must first be
  // allocated.  The coordinates of the origin can then be assigned to
  // every component.  These coordinates correspond to the position of
  // the first pixel of the image with respect to an arbitrary
  // reference system in physical space. It is the user's
  // responsibility to make sure that multiple images used in the same
  // application are using a consistent reference system. This is
  // extremely important in image registration applications.
  // The following code illustrates the creation and assignment of a variable
  // suitable for initializing the image origin.
  // \index{otb::Image!origin}
  // \index{otb::Image!SetOrigin()}

  ImageType::PointType origin;

  origin[0] = 0.0; // coordinates of the
  origin[1] = 0.0; // first pixel in 2-D


  //  The origin can also be retrieved from an image by using the
  //  \code{GetOrigin()} method. This will return a reference to a
  //  \code{Point}. The reference can be used to read the contents of
  //  the array. Note again the use of the \code{const} keyword to indicate
  //  that the array contents will not be modified.

  const ImageType::PointType& orgn = image->GetOrigin();

  std::cout << "Origin = ";
  std::cout << orgn[0] << ", " << orgn[1] << std::endl;

  // Once the spacing and origin of the image have been initialized, the image
  // will correctly map pixel indices to and from physical space
  // coordinates. The following code illustrates how a point in physical
  // space can be mapped into an image index for the purpose of reading the
  // content of the closest pixel.
  // First, a \doxygen{itk}{Point} type must be declared. The point type is
  // templated over the type used to represent coordinates and over the
  // dimension of the space. In this particular case, the dimension of the
  // point must match the dimension of the image.

  using PointType = itk::Point<double, ImageType::ImageDimension>;

  // The Point class, like an \doxygen{itk}{Index}, is a relatively small and
  // simple object.  For this reason, it is not reference-counted like the
  // large data objects in OTB.  Consequently, it is also not manipulated
  // with \doxygen{itk}{SmartPointer}s.  Point objects are simply declared as
  // instances of any other C++ class.  Once the point is declared, its
  // components can be accessed using traditional array notation. In
  // particular, the \code{[]} operator is available. For efficiency reasons,
  // no bounds checking is performed on the index used to access a particular
  // point component. It is the user's responsibility to make sure that the
  // index is in the range $\{0, Dimension-1\}$.

  PointType point;

  point[0] = 1.45; // x coordinate
  point[1] = 7.21; // y coordinate

  // The image will map the point to an index using the values of the
  // current spacing and origin. An index object must be provided to
  // receive the results of the mapping. The index object can be
  // instantiated by using the \code{IndexType} defined in the Image
  // type.

  ImageType::IndexType pixelIndex;

  // The \code{TransformPhysicalPointToIndex()} method of the image class
  // will compute the pixel index closest to the point provided. The method
  // checks for this index to be contained inside the current buffered pixel
  // data. The method returns a boolean indicating whether the resulting
  // index falls inside the buffered region or not. The output index should
  // not be used when the returned value of the method is \code{false}.
  // The following lines illustrate the point to index mapping and the
  // subsequent use of the pixel index for accessing pixel data from the
  // image.
  // \index{otb::Image!TransformPhysicalPointToIndex()}

  bool isInside = image->TransformPhysicalPointToIndex(point, pixelIndex);

  if (isInside)
    ImageType::PixelType pixelValue = image->GetPixel(pixelIndex);

    pixelValue += 5;

    image->SetPixel(pixelIndex, pixelValue);

  // Remember that \code{GetPixel()} and \code{SetPixel()} are very
  // inefficient methods for accessing pixel data. Image iterators should be
  // used when massive access to pixel data is required.

  return EXIT_SUCCESS;