WCSLIB 4.17: sph.h Source File

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# sph.h

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    00001 /*============================================================================
    00002
    00003   WCSLIB 4.17 - an implementation of the FITS WCS standard.
    00004   Copyright (C) 1995-2013, Mark Calabretta
    00005
    00006   This file is part of WCSLIB.
    00007
    00008   WCSLIB is free software: you can redistribute it and/or modify it under the
    00009   terms of the GNU Lesser General Public License as published by the Free
    00010   Software Foundation, either version 3 of the License, or (at your option)
    00011   any later version.
    00012
    00013   WCSLIB is distributed in the hope that it will be useful, but WITHOUT ANY
    00014   WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
    00015   FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for
    00016   more details.
    00017
    00018   You should have received a copy of the GNU Lesser General Public License
    00019   along with WCSLIB.  If not, see http://www.gnu.org/licenses.
    00020
    00021   Direct correspondence concerning WCSLIB to mark@calabretta.id.au
    00022
    00023   Author: Mark Calabretta, Australia Telescope National Facility, CSIRO.
    00024   http://www.atnf.csiro.au/people/Mark.Calabretta
    00025   $Id: sph.h,v 4.17 2013/01/29 05:29:20 cal103 Exp $
    00026 *=============================================================================
    00027 *
    00028 * WCSLIB 4.17 - C routines that implement the spherical coordinate
    00029 * transformations used by the FITS World Coordinate System (WCS) standard.
    00030 * Refer to
    00031 *
    00032 *   "Representations of world coordinates in FITS",
    00033 *   Greisen, E.W., & Calabretta, M.R. 2002, A&A, 395, 1061 (Paper I)
    00034 *
    00035 *   "Representations of celestial coordinates in FITS",
    00036 *   Calabretta, M.R., & Greisen, E.W. 2002, A&A, 395, 1077 (Paper II)
    00037 *
    00038 * Refer to the README file provided with WCSLIB for an overview of the
    00039 * library.
    00040 *
    00041 *
    00042 * Summary of the sph routines
    00043 * ---------------------------
    00044 * The WCS spherical coordinate transformations are implemented via separate
    00045 * functions, sphx2s() and sphs2x(), for the transformation in each direction.
    00046 *
    00047 * A utility function, sphdpa(), computes the angular distances and position
    00048 * angles from a given point on the sky to a number of other points.  sphpad()
    00049 * does the complementary operation - computes the coordinates of points offset
    00050 * by the given angular distances and position angles from a given point on the
    00051 * sky.
    00052 *
    00053 *
    00054 * sphx2s() - Rotation in the pixel-to-world direction
    00055 * ---------------------------------------------------
    00056 * sphx2s() transforms native coordinates of a projection to celestial
    00057 * coordinates.
    00058 *
    00059 * Given:
    00060 *   eul       const double[5]
    00061 *                       Euler angles for the transformation:
    00062 *                         0: Celestial longitude of the native pole [deg].
    00063 *                         1: Celestial colatitude of the native pole, or
    00064 *                            native colatitude of the celestial pole [deg].
    00065 *                         2: Native longitude of the celestial pole [deg].
    00066 *                         3: cos(eul[1])
    00067 *                         4: sin(eul[1])
    00068 *
    00069 *   nphi,
    00070 *   ntheta    int       Vector lengths.
    00071 *
    00072 *   spt,sxy   int       Vector strides.
    00073 *
    00074 *   phi,theta const double[]
    00075 *                       Longitude and latitude in the native coordinate
    00076 *                       system of the projection [deg].
    00077 *
    00078 * Returned:
    00079 *   lng,lat   double[]  Celestial longitude and latitude [deg].  These may
    00080 *                       refer to the same storage as phi and theta
    00081 *                       respectively.
    00082 *
    00083 * Function return value:
    00084 *             int       Status return value:
    00085 *                         0: Success.
    00086 *
    00087 *
    00088 * sphs2x() - Rotation in the world-to-pixel direction
    00089 * ---------------------------------------------------
    00090 * sphs2x() transforms celestial coordinates to the native coordinates of a
    00091 * projection.
    00092 *
    00093 * Given:
    00094 *   eul       const double[5]
    00095 *                       Euler angles for the transformation:
    00096 *                         0: Celestial longitude of the native pole [deg].
    00097 *                         1: Celestial colatitude of the native pole, or
    00098 *                            native colatitude of the celestial pole [deg].
    00099 *                         2: Native longitude of the celestial pole [deg].
    00100 *                         3: cos(eul[1])
    00101 *                         4: sin(eul[1])
    00102 *
    00103 *   nlng,nlat int       Vector lengths.
    00104 *
    00105 *   sll,spt   int       Vector strides.
    00106 *
    00107 *   lng,lat   const double[]
    00108 *                       Celestial longitude and latitude [deg].
    00109 *
    00110 * Returned:
    00111 *   phi,theta double[]  Longitude and latitude in the native coordinate system
    00112 *                       of the projection [deg].  These may refer to the same
    00113 *                       storage as lng and lat respectively.
    00114 *
    00115 * Function return value:
    00116 *             int       Status return value:
    00117 *                         0: Success.
    00118 *
    00119 *
    00120 * sphdpa() - Compute angular distance and position angle
    00121 * ------------------------------------------------------
    00122 * sphdpa() computes the angular distance and generalized position angle (see
    00123 * notes) from a "reference" point to a number of "field" points on the sphere.
    00124 * The points must be specified consistently in any spherical coordinate
    00125 * system.
    00126 *
    00127 * sphdpa() is complementary to sphpad().
    00128 *
    00129 * Given:
    00130 *   nfield    int       The number of field points.
    00131 *
    00132 *   lng0,lat0 double    Spherical coordinates of the reference point [deg].
    00133 *
    00134 *   lng,lat   const double[]
    00135 *                       Spherical coordinates of the field points [deg].
    00136 *
    00137 * Returned:
    00138 *   dist,pa   double[]  Angular distances and position angles [deg].  These
    00139 *                       may refer to the same storage as lng and lat
    00140 *                       respectively.
    00141 *
    00142 * Function return value:
    00143 *             int       Status return value:
    00144 *                         0: Success.
    00145 *
    00146 * Notes:
    00147 *   sphdpa() uses sphs2x() to rotate coordinates so that the reference point
    00148 *   is at the north pole of the new system with the north pole of the old
    00149 *   system at zero longitude in the new.  The Euler angles required by
    00150 *   sphs2x() for this rotation are
    00151 *
    00152 =     eul[0] = lng0;
    00153 =     eul[1] = 90.0 - lat0;
    00154 =     eul[2] =  0.0;
    00155 *
    00156 *   The angular distance and generalized position angle are readily obtained
    00157 *   from the longitude and latitude of the field point in the new system.
    00158 *   This applies even if the reference point is at one of the poles, in which
    00159 *   case the "position angle" returned is as would be computed for a reference
    00160 *   point at (lng0,+90-epsilon) or (lng0,-90+epsilon), in the limit as epsilon
    00161 *   goes to zero.
    00162 *
    00163 *   It is evident that the coordinate system in which the two points are
    00164 *   expressed is irrelevant to the determination of the angular separation
    00165 *   between the points.  However, this is not true of the generalized position
    00166 *   angle.
    00167 *
    00168 *   The generalized position angle is here defined as the angle of
    00169 *   intersection of the great circle containing the reference and field points
    00170 *   with that containing the reference point and the pole.  It has its normal
    00171 *   meaning when the the reference and field points are specified in
    00172 *   equatorial coordinates (right ascension and declination).
    00173 *
    00174 *   Interchanging the reference and field points changes the position angle in
    00175 *   a non-intuitive way (because the sum of the angles of a spherical triangle
    00176 *   normally exceeds 180 degrees).
    00177 *
    00178 *   The position angle is undefined if the reference and field points are
    00179 *   coincident or antipodal.  This may be detected by checking for a distance
    00180 *   of 0 or 180 degrees (within rounding tolerance).  sphdpa() will return an
    00181 *   arbitrary position angle in such circumstances.
    00182 *
    00183 *
    00184 * sphpad() - Compute field points offset from a given point
    00185 * ---------------------------------------------------------
    00186 * sphpad() computes the coordinates of a set of points that are offset by the
    00187 * specified angular distances and position angles from a given "reference"
    00188 * point on the sky.  The distances and position angles must be specified
    00189 * consistently in any spherical coordinate system.
    00190 *
    00191 * sphpad() is complementary to sphdpa().
    00192 *
    00193 * Given:
    00194 *   nfield    int       The number of field points.
    00195 *
    00196 *   lng0,lat0 double    Spherical coordinates of the reference point [deg].
    00197 *
    00198 *   dist,pa   const double[]
    00199 *                       Angular distances and position angles [deg].
    00200 *
    00201 * Returned:
    00202 *   lng,lat   double[]  Spherical coordinates of the field points [deg].
    00203 *                       These may refer to the same storage as dist and pa
    00204 *                       respectively.
    00205 *
    00206 * Function return value:
    00207 *             int       Status return value:
    00208 *                         0: Success.
    00209 *
    00210 * Notes:
    00211 *   sphpad() is implemented analogously to sphdpa() although using sphx2s()
    00212 *   for the inverse transformation.  In particular, when the reference point
    00213 *   is at one of the poles, "position angle" is interpreted as though the
    00214 *   reference point was at (lng0,+90-epsilon) or (lng0,-90+epsilon), in the
    00215 *   limit as epsilon goes to zero.
    00216 *
    00217 *   Applying sphpad() with the distances and position angles computed by
    00218 *   sphdpa() should return the original field points.
    00219 *
    00220 *===========================================================================*/
    00221
    00222 #ifndef WCSLIB_SPH
    00223 #define WCSLIB_SPH
    00224
    00225 #ifdef __cplusplus
    00226 extern "C" {
    00227 #endif
    00228
    00229
    00230 int sphx2s(const double eul[5], int nphi, int ntheta, int spt, int sxy,
    00231            const double phi[], const double theta[],
    00232            double lng[], double lat[]);
    00233
    00234 int sphs2x(const double eul[5], int nlng, int nlat, int sll , int spt,
    00235            const double lng[], const double lat[],
    00236            double phi[], double theta[]);
    00237
    00238 int sphdpa(int nfield, double lng0, double lat0,
    00239            const double lng[], const double lat[],
    00240            double dist[], double pa[]);
    00241
    00242 int sphpad(int nfield, double lng0, double lat0,
    00243            const double dist[], const double pa[],
    00244            double lng[], double lat[]);
    00245
    00246
    00247 #ifdef __cplusplus
    00248 }
    00249 #endif
    00250
    00251 #endif /* WCSLIB_SPH */