AxesSpecifier.h

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// # AxesSpecifier.h: Specification of axes to keep or remove
// # Copyright (C) 2000
// # Associated Universities, Inc. Washington DC, USA.
// #
// # This library is free software; you can redistribute it and/or modify it
// # under the terms of the GNU Library General Public License as published by
// # the Free Software Foundation; either version 2 of the License, or (at your
// # option) any later version.
// #
// # This library is distributed in the hope that it will be useful, but WITHOUT
// # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// # FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
// # License for more details.
// #
// # You should have received a copy of the GNU Library General Public License
// # along with this library; if not, write to the Free Software Foundation,
// # Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
// #
// # Correspondence concerning AIPS++ should be addressed as follows:
// #        Internet email: casa-feedback@nrao.edu.
// #        Postal address: AIPS++ Project Office
// #                        National Radio Astronomy Observatory
// #                        520 Edgemont Road
// #                        Charlottesville, VA 22903-2475 USA
 
#ifndef CASA_AXESSPECIFIER_2_H
#define CASA_AXESSPECIFIER_2_H
 
// # Includes
#include "IPosition.h"
#include "AxesMapping.h"
 
namespace casacore {  // # NAMESPACE CASACORE - BEGIN
 
// # Forward Declarations
 
// <summary>
// Specification of axes to keep or remove
// </summary>
 
// <use visibility=export>
 
// <reviewed reviewer="" date="yyyy/mm/dd" tests="tAxesSpecifier.cc" demos="">
// </reviewed>
 
// <prerequisite>
//   <li> <linkto class="IPosition">IPosition</linkto>
// </prerequisite>
 
// <synopsis>
// AxesSpecifier makes it possible to specify which axes should
// be used in a shape. Degenerate axes (i.e. axes with length 0)
// can be thrown away which makes it possible to reduce the
// dimensionality of an array. All degenerate axes can be thrown
// away, but one can also specify which ones should be kept.
// <p>
// Another option of this class is to reorder the axes, thus to
// make the axes of a lattice appear in a different order.
// This can be useful when two images with diferent axes orders
// have to be combined.
// <p>
// When an AxesSpecifier has to be used for a lattice, the lattice's
// shape has to be applied to the AxesSpecifier. The result is
// a <linkto class=AxesMapping>AxesMapping</linkto> object.
// This object is (for example) used internally in the
// casacore SubLattice class to know how
// to map the axes form the original lattice to the sublattice.
// <note role=caution>
// Reordering axes is not supported (yet) by the other Casacore classes
// like Lattices and Images.
// </note>
// </synopsis>
 
// <example>
// This example tells that all degenerate axes have to be kept.
// The axes are reordered to 1,0,2. Thus the first and second axes are
// swapped.
// <srcblock>
// AxesSpecifier spec(true, IPosition(3,1,0,2));
// AxesMapping map = spec.apply (IPosition(3,4,1,5));
// AlwaysAssertExit (map.posToNew (IPosition(3,2,0,3)) == IPosition(3,0,2,3));
// AlwaysAssertExit (map.posToOld (IPosition(3,0,2,3)) == IPosition(3,2,0,3));
//
// The following specification would have the same effect, because the
// unspecified axes are kept in their natural order.
// AxesSpecifier spec(true, IPosition(1,1));
// </srcblock>
//
// The same example as above, but now degenerated axes are removed.
// Note that because the second axis is removed, the third axis now
// get the second axis, thus gets swapped with the first axis.
// <br>Also note the difference between the functions <src>posToOld</src>
// and <src>shapeToOld</src>.
// <srcblock>
// AxesSpecifier spec(false, IPosition(1,1));
// AxesMapping map = spec.apply (IPosition(3,4,1,5));
// AlwaysAssertExit (map.posToNew (IPosition(3,2,0,3)) == IPosition(2,3,2));
// AlwaysAssertExit (map.posToOld (IPosition(3,3,2)) == IPosition(3,2,0,3);
// AlwaysAssertExit (map.shapeToOld (IPosition(3,3,2)) == IPosition(3,2,1,3);
// </srcblock>
// </example>
 
// # <todo asof="yyyy/mm/dd">
// # </todo>
 
class AxesSpecifier {
 public:
  // The default constructor keeps all axes.
  AxesSpecifier();
 
  // Tell if no or all degenerate axes have to be removed.
  explicit AxesSpecifier(bool keepDegenerate);
 
  // Tell if no or all degenerate axes have to be removed.
  // <br>The argument <src>axisPath</src> makes it possible to specify in
  // which order the KEPT axes have to be used. Unspecified axes are
  // appended to the end. It gives a means to reorder the axes of a lattice.
  // <br>E.g. for a 4-dim lattice axisPath [2,0] means axis order [2,0,1,3].
  explicit AxesSpecifier(bool keepDegenerate, const IPosition& axisPath);
 
  // Tell which (degenerate) axes have to be kept.
  // Non-degenerate axes will always be kept.
  explicit AxesSpecifier(const IPosition& keepAxes);
 
  // The argument <src>keepAxes</src> tells which degenerate axes have
  // to be kept. Non-degenerate axes will always be kept.
  // <br>The argument <src>axisPath</src> makes it possible to specify in
  // which order the KEPT axes have to be used. Unspecified axes are
  // appended to the end. It gives a means to reorder the axes of a lattice.
  // <br>E.g. for a 4-dim lattice axisPath [2,0] means axis order [2,0,1,3].
  AxesSpecifier(const IPosition& keepAxes, const IPosition& axisPath);
 
  // Apply the specification to a shape.
  // It returns an <linkto class=AxesMapping>AxesMapping</linkto>
  // object which takes care of mapping old to new axes order.
  AxesMapping apply(const IPosition& shape) const;
 
  // Are we keeping all degenerate axes ?
  bool keep() const { return itsKeep; };
 
 private:
  IPosition itsAxes;
  IPosition itsPath;
  bool itsKeep;
};
 
}  // namespace casacore
 
#endif