| 1 | /*
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| 2 | *+
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| 3 | * Name:
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| 4 | * palPlanel
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| 5 |
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| 6 | * Purpose:
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| 7 | * Transform conventional elements into position and velocity
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| 8 |
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| 9 | * Language:
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| 10 | * Starlink ANSI C
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| 11 |
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| 12 | * Type of Module:
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| 13 | * Library routine
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| 14 |
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| 15 | * Invocation:
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| 16 | * void palPlanel ( double date, int jform, double epoch, double orbinc,
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| 17 | * double anode, double perih, double aorq, double e,
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| 18 | * double aorl, double dm, double pv[6], int *jstat );
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| 19 |
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| 20 | * Arguments:
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| 21 | * date = double (Given)
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| 22 | * Epoch (TT MJD) of osculation (Note 1)
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| 23 | * jform = int (Given)
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| 24 | * Element set actually returned (1-3; Note 3)
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| 25 | * epoch = double (Given)
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| 26 | * Epoch of elements (TT MJD) (Note 4)
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| 27 | * orbinc = double (Given)
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| 28 | * inclination (radians)
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| 29 | * anode = double (Given)
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| 30 | * longitude of the ascending node (radians)
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| 31 | * perih = double (Given)
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| 32 | * longitude or argument of perihelion (radians)
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| 33 | * aorq = double (Given)
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| 34 | * mean distance or perihelion distance (AU)
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| 35 | * e = double (Given)
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| 36 | * eccentricity
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| 37 | * aorl = double (Given)
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| 38 | * mean anomaly or longitude (radians, JFORM=1,2 only)
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| 39 | * dm = double (Given)
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| 40 | * daily motion (radians, JFORM=1 only)
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| 41 | * u = double [13] (Returned)
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| 42 | * Universal orbital elements (Note 1)
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| 43 | * (0) combined mass (M+m)
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| 44 | * (1) total energy of the orbit (alpha)
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| 45 | * (2) reference (osculating) epoch (t0)
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| 46 | * (3-5) position at reference epoch (r0)
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| 47 | * (6-8) velocity at reference epoch (v0)
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| 48 | * (9) heliocentric distance at reference epoch
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| 49 | * (10) r0.v0
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| 50 | * (11) date (t)
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| 51 | * (12) universal eccentric anomaly (psi) of date, approx
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| 52 | * jstat = int * (Returned)
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| 53 | * status: 0 = OK
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| 54 | * - -1 = illegal JFORM
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| 55 | * - -2 = illegal E
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| 56 | * - -3 = illegal AORQ
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| 57 | * - -4 = illegal DM
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| 58 | * - -5 = numerical error
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| 59 |
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| 60 | * Description:
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| 61 | * Heliocentric position and velocity of a planet, asteroid or comet,
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| 62 | * starting from orbital elements.
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| 63 |
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| 64 | * Authors:
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| 65 | * PTW: Pat Wallace (STFC)
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| 66 | * TIMJ: Tim Jenness (JAC, Hawaii)
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| 67 | * {enter_new_authors_here}
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| 68 |
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| 69 | * Notes:
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| 70 | * - DATE is the instant for which the prediction is required. It is
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| 71 | * in the TT timescale (formerly Ephemeris Time, ET) and is a
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| 72 | * Modified Julian Date (JD-2400000.5).
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| 73 | * - The elements are with respect to the J2000 ecliptic and equinox.
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| 74 | * - A choice of three different element-set options is available:
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| 75 | *
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| 76 | * Option JFORM = 1, suitable for the major planets:
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| 77 | *
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| 78 | * EPOCH = epoch of elements (TT MJD)
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| 79 | * ORBINC = inclination i (radians)
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| 80 | * ANODE = longitude of the ascending node, big omega (radians)
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| 81 | * PERIH = longitude of perihelion, curly pi (radians)
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| 82 | * AORQ = mean distance, a (AU)
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| 83 | * E = eccentricity, e (range 0 to <1)
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| 84 | * AORL = mean longitude L (radians)
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| 85 | * DM = daily motion (radians)
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| 86 | *
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| 87 | * Option JFORM = 2, suitable for minor planets:
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| 88 | *
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| 89 | * EPOCH = epoch of elements (TT MJD)
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| 90 | * ORBINC = inclination i (radians)
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| 91 | * ANODE = longitude of the ascending node, big omega (radians)
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| 92 | * PERIH = argument of perihelion, little omega (radians)
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| 93 | * AORQ = mean distance, a (AU)
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| 94 | * E = eccentricity, e (range 0 to <1)
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| 95 | * AORL = mean anomaly M (radians)
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| 96 | *
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| 97 | * Option JFORM = 3, suitable for comets:
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| 98 | *
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| 99 | * EPOCH = epoch of elements and perihelion (TT MJD)
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| 100 | * ORBINC = inclination i (radians)
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| 101 | * ANODE = longitude of the ascending node, big omega (radians)
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| 102 | * PERIH = argument of perihelion, little omega (radians)
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| 103 | * AORQ = perihelion distance, q (AU)
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| 104 | * E = eccentricity, e (range 0 to 10)
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| 105 | *
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| 106 | * Unused arguments (DM for JFORM=2, AORL and DM for JFORM=3) are not
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| 107 | * accessed.
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| 108 | * - Each of the three element sets defines an unperturbed heliocentric
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| 109 | * orbit. For a given epoch of observation, the position of the body
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| 110 | * in its orbit can be predicted from these elements, which are
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| 111 | * called "osculating elements", using standard two-body analytical
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| 112 | * solutions. However, due to planetary perturbations, a given set
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| 113 | * of osculating elements remains usable for only as long as the
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| 114 | * unperturbed orbit that it describes is an adequate approximation
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| 115 | * to reality. Attached to such a set of elements is a date called
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| 116 | * the "osculating epoch", at which the elements are, momentarily,
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| 117 | * a perfect representation of the instantaneous position and
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| 118 | * velocity of the body.
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| 119 | *
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| 120 | * Therefore, for any given problem there are up to three different
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| 121 | * epochs in play, and it is vital to distinguish clearly between
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| 122 | * them:
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| 123 | *
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| 124 | * . The epoch of observation: the moment in time for which the
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| 125 | * position of the body is to be predicted.
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| 126 | *
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| 127 | * . The epoch defining the position of the body: the moment in time
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| 128 | * at which, in the absence of purturbations, the specified
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| 129 | * position (mean longitude, mean anomaly, or perihelion) is
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| 130 | * reached.
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| 131 | *
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| 132 | * . The osculating epoch: the moment in time at which the given
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| 133 | * elements are correct.
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| 134 | *
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| 135 | * For the major-planet and minor-planet cases it is usual to make
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| 136 | * the epoch that defines the position of the body the same as the
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| 137 | * epoch of osculation. Thus, only two different epochs are
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| 138 | * involved: the epoch of the elements and the epoch of observation.
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| 139 | *
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| 140 | * For comets, the epoch of perihelion fixes the position in the
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| 141 | * orbit and in general a different epoch of osculation will be
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| 142 | * chosen. Thus, all three types of epoch are involved.
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| 143 | *
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| 144 | * For the present routine:
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| 145 | *
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| 146 | * . The epoch of observation is the argument DATE.
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| 147 | *
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| 148 | * . The epoch defining the position of the body is the argument
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| 149 | * EPOCH.
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| 150 | *
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| 151 | * . The osculating epoch is not used and is assumed to be close
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| 152 | * enough to the epoch of observation to deliver adequate accuracy.
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| 153 | * If not, a preliminary call to palPertel may be used to update
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| 154 | * the element-set (and its associated osculating epoch) by
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| 155 | * applying planetary perturbations.
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| 156 | * - The reference frame for the result is with respect to the mean
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| 157 | * equator and equinox of epoch J2000.
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| 158 | * - The algorithm was originally adapted from the EPHSLA program of
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| 159 | * D.H.P.Jones (private communication, 1996). The method is based
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| 160 | * on Stumpff's Universal Variables.
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| 161 |
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| 162 | * See Also:
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| 163 | * Everhart, E. & Pitkin, E.T., Am.J.Phys. 51, 712, 1983.
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| 164 |
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| 165 | * History:
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| 166 | * 2012-03-12 (TIMJ):
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| 167 | * Initial version taken directly from SLA/F.
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| 168 | * Adapted with permission from the Fortran SLALIB library.
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| 169 | * {enter_further_changes_here}
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| 170 |
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| 171 | * Copyright:
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| 172 | * Copyright (C) 2002 Rutherford Appleton Laboratory
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| 173 | * Copyright (C) 2012 Science and Technology Facilities Council.
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| 174 | * All Rights Reserved.
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| 175 |
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| 176 | * Licence:
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| 177 | * This program is free software; you can redistribute it and/or
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| 178 | * modify it under the terms of the GNU General Public License as
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| 179 | * published by the Free Software Foundation; either version 3 of
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| 180 | * the License, or (at your option) any later version.
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| 181 | *
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| 182 | * This program is distributed in the hope that it will be
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| 183 | * useful, but WITHOUT ANY WARRANTY; without even the implied
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| 184 | * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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| 185 | * PURPOSE. See the GNU General Public License for more details.
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| 186 | *
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| 187 | * You should have received a copy of the GNU General Public License
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| 188 | * along with this program; if not, write to the Free Software
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| 189 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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| 190 | * MA 02110-1301, USA.
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| 191 |
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| 192 | * Bugs:
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| 193 | * {note_any_bugs_here}
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| 194 | *-
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| 195 | */
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| 196 |
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| 197 | #include "pal.h"
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| 198 |
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| 199 |
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| 200 | void palPlanel ( double date, int jform, double epoch, double orbinc,
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| 201 | double anode, double perih, double aorq, double e,
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| 202 | double aorl, double dm, double pv[6], int *jstat ) {
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| 203 |
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| 204 | int j;
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| 205 | double u[13];
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| 206 |
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| 207 | /* Validate elements and convert to "universal variables" parameters. */
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| 208 | palEl2ue( date, jform, epoch, orbinc, anode, perih, aorq, e, aorl,
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| 209 | dm, u, &j );
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| 210 |
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| 211 | /* Determine the position and velocity */
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| 212 | if (j == 0) {
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| 213 | palUe2pv( date, u, pv, &j);
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| 214 | if (j != 0) j = -5;
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| 215 | }
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| 216 |
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| 217 | /* Wrap up */
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| 218 | *jstat = j;
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| 219 |
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| 220 | }
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