SolarPos.h

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// # SolarPos.h: Solar position class
// # Copyright (C) 1995,1996,1997,1998
// # 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 MEASURES_SOLARPOS_H
#define MEASURES_SOLARPOS_H
 
// # Includes
#include <mutex>
 
#include <casacore/casa/aips.h>
#include <casacore/casa/Quanta/MVPosition.h>
 
namespace casacore {  // # NAMESPACE CASACORE - BEGIN
 
// <summary> Solar position class and calculations </summary>
 
// <use visibility=export>
 
// <reviewed reviewer="UNKNOWN" date="before2004/08/25" tests="tMeasMath" demos="">
// </reviewed>
 
// <prerequisite>
//   <li> <linkto class=Measure>Measure</linkto> class,
//      especially <linkto class=MEpoch>MEpoch</linkto>
//   <li> <linkto class=MeasData>MeasData</linkto> class for constants
// </prerequisite>
//
// <etymology>
// SolarPos from Solar Position
// </etymology>
//
// <synopsis>
// SolarPos forms the class for Solar Position calculations. It is a simple
// container with the selected method, and the mean epoch.<br>
// The method is selected from one of the following:
// <ul>
//   <li> SolarPos::STANDARD   (at 1995/09/04 the IAU1980 definition)
//   <li> SolarPos::NONE
// </ul>
// Epochs can be specified as the MJD (with defined constants MeasData::MJD2000
// and MeasData::MJDB1950 or the actual MJD),
// leading to the following constructors:
// <ul>
//   <li> SolarPos() default; assuming JD2000, IAU1980
//   <li> SolarPos(method) assuming the correct default epoch of
//      JD2000
//   <li> SolarPos(method,epoch) with epoch Double(MJD)
// </ul>
// Actual SolarPos for a certain Epoch is calculated by the () operator
// as SolarPos(epoch), with epoch Double MJD, as an MVPosition vector.<br>
// It returns the geocentric position of the heliocentre in rectangular
// coordinates in AU.<br>
// The derivative (d<sup>-1</sup>) can be obtained as well by
// derivative(epoch), baryEarthDerivative() and barySunDerivative().<br>
// The Earth's and solar barycentric position can be obtained by the
// members <src>baryEarth</src> and <src>barySun</src>.
// The following details can be set with the
// <linkto class=Aipsrc>Aipsrc</linkto> mechanism:
// <ul>
//  <li> measures.solarpos.d_interval: approximation interval as time
//  (fraction of days is default unit) over which linear approximation
//  is used
//  <li> measures.solarpos.b_usejpl: use the JPL database for solar position.
//  Else analytical expression, relative error about 10<sup>-9</sup>
//  Note that the JPL database to be used can be set with
//      measures.jpl.ephemeris (at the moment of writing DE200 (default),
//      or DE405)
// </ul>
// Reference: M. Soma et al., Cel. Mech. 41 (1988), 389;
// E.M. Standish, Astron. Astroph. 114 (1982), 297.
// </synopsis>
//
// <example>
// </example>
//
// <motivation>
// To calculate the solar/Earth positions for gravitational deflection.
// An alternate route could have been
// a global function, but having a simple container allows
// caching of some calculations for speed.<br>
// Using MJD (JD-2400000.5) rather than JD is for precision reasons.
// </motivation>
//
// <todo asof="1996/02/18">
// </todo>
 
class SolarPos {
 public:
  // # Constants
  //  Interval to be used for linear approximation (in days)
  static constexpr Double INTV = 0.04;
 
  // # Enumerations
  //  Types of known SolarPos calculations (at 1995/09/04 STANDARD == IAU1980)
  enum SolarPosTypes { STANDARD, NONE };
 
  // # Constructors
  //  Default constructor, generates default J2000 SolarPos identification
  SolarPos();
  // Copy constructor
  SolarPos(const SolarPos &other);
  // Constructor with type
  SolarPos(SolarPosTypes type);
  // Copy assignment
  SolarPos &operator=(const SolarPos &other);
 
  // # Destructor
  ~SolarPos();
 
  // # Operators
  //  Operator () calculates the geocentric Solar Position in AU
  const MVPosition &operator()(Double epoch);
 
  // # General Member Functions
  //  <group>
  //  Return derivatives of SolarPos (d<sup>-1</sup>)
  const MVPosition &derivative(Double epoch);
  const MVPosition &baryEarthDerivative(Double epoch);
  const MVPosition &barySunDerivative(Double epoch);
  // </group>
  // Barycentric position of Earth
  const MVPosition &baryEarth(Double epoch);
  // Barycentric position of Sun
  const MVPosition &barySun(Double epoch);
 
  // Re-initialise SolarPos object
  // <group>
  void init();
  void init(SolarPosTypes type);
  // </group>
 
  // Refresh calculations
  void refresh();
 
 private:
  // # Data menbers
  //  Method to be used
  SolarPosTypes method;
  // Check epoch for linear approximation
  Double checkEpoch = 1e30;
  Double checkSunEpoch = 1e30;
  // Cached calculated Earth positions
  Double eval[3];
  // Cached derivatives
  Double deval[3];
  // Cached calculated Sun positions
  Double sval[3];
  // Cached derivatives
  Double dsval[3];
  // To be able to use references in simple calculations, results are calculated
  // in a circular buffer.
  // Current buffer pointer
  Int lres;
  // Last calculation
  MVPosition result[6];
  // Interpolation interval
  inline static uInt interval_reg;
  // JPL use
  inline static uInt usejpl_reg;
  inline static std::once_flag initialize_once_flag;
 
  // # Member functions
  void copy(const SolarPos &other);
  static void initialize_statics();
  // Calculate heliocentric Earth position for time t
  void calcEarth(Double t);
  // Calculate heliocentric barycentre position
  void calcSun(Double t);
};
 
}  // namespace casacore
 
#endif