| 1 | /*
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| 2 | *+
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| 3 | * Name:
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| 4 | * palAop
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| 5 |
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| 6 | * Purpose:
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| 7 | * Apparent to observed place
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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 palAop ( double rap, double dap, double date, double dut,
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| 17 | * double elongm, double phim, double hm, double xp,
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| 18 | * double yp, double tdk, double pmb, double rh,
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| 19 | * double wl, double tlr,
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| 20 | * double *aob, double *zob, double *hob,
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| 21 | * double *dob, double *rob );
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| 22 |
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| 23 | * Arguments:
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| 24 | * rap = double (Given)
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| 25 | * Geocentric apparent right ascension
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| 26 | * dap = double (Given)
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| 27 | * Geocentirc apparent declination
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| 28 | * date = double (Given)
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| 29 | * UTC date/time (Modified Julian Date, JD-2400000.5)
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| 30 | * dut = double (Given)
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| 31 | * delta UT: UT1-UTC (UTC seconds)
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| 32 | * elongm = double (Given)
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| 33 | * Mean longitude of the observer (radians, east +ve)
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| 34 | * phim = double (Given)
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| 35 | * Mean geodetic latitude of the observer (radians)
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| 36 | * hm = double (Given)
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| 37 | * Observer's height above sea level (metres)
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| 38 | * xp = double (Given)
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| 39 | * Polar motion x-coordinates (radians)
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| 40 | * yp = double (Given)
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| 41 | * Polar motion y-coordinates (radians)
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| 42 | * tdk = double (Given)
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| 43 | * Local ambient temperature (K; std=273.15)
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| 44 | * pmb = double (Given)
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| 45 | * Local atmospheric pressure (mb; std=1013.25)
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| 46 | * rh = double (Given)
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| 47 | * Local relative humidity (in the range 0.0-1.0)
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| 48 | * wl = double (Given)
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| 49 | * Effective wavelength (micron, e.g. 0.55)
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| 50 | * tlr = double (Given)
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| 51 | * Tropospheric laps rate (K/metre, e.g. 0.0065)
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| 52 | * aob = double * (Returned)
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| 53 | * Observed azimuth (radians: N=0; E=90)
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| 54 | * zob = double * (Returned)
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| 55 | * Observed zenith distance (radians)
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| 56 | * hob = double * (Returned)
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| 57 | * Observed Hour Angle (radians)
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| 58 | * dob = double * (Returned)
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| 59 | * Observed Declination (radians)
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| 60 | * rob = double * (Returned)
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| 61 | * Observed Right Ascension (radians)
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| 62 |
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| 63 |
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| 64 | * Description:
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| 65 | * Apparent to observed place for sources distant from the solar system.
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| 66 |
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| 67 | * Authors:
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| 68 | * PTW: Patrick T. Wallace
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| 69 | * TIMJ: Tim Jenness (JAC, Hawaii)
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| 70 | * {enter_new_authors_here}
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| 71 |
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| 72 | * Notes:
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| 73 | * - This routine returns zenith distance rather than elevation
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| 74 | * in order to reflect the fact that no allowance is made for
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| 75 | * depression of the horizon.
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| 76 | *
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| 77 | * - The accuracy of the result is limited by the corrections for
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| 78 | * refraction. Providing the meteorological parameters are
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| 79 | * known accurately and there are no gross local effects, the
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| 80 | * predicted apparent RA,Dec should be within about 0.1 arcsec
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| 81 | * for a zenith distance of less than 70 degrees. Even at a
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| 82 | * topocentric zenith distance of 90 degrees, the accuracy in
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| 83 | * elevation should be better than 1 arcmin; useful results
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| 84 | * are available for a further 3 degrees, beyond which the
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| 85 | * palRefro routine returns a fixed value of the refraction.
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| 86 | * The complementary routines palAop (or palAopqk) and palOap
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| 87 | * (or palOapqk) are self-consistent to better than 1 micro-
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| 88 | * arcsecond all over the celestial sphere.
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| 89 | *
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| 90 | * - It is advisable to take great care with units, as even
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| 91 | * unlikely values of the input parameters are accepted and
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| 92 | * processed in accordance with the models used.
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| 93 | *
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| 94 | * - "Apparent" place means the geocentric apparent right ascension
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| 95 | * and declination, which is obtained from a catalogue mean place
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| 96 | * by allowing for space motion, parallax, precession, nutation,
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| 97 | * annual aberration, and the Sun's gravitational lens effect. For
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| 98 | * star positions in the FK5 system (i.e. J2000), these effects can
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| 99 | * be applied by means of the palMap etc routines. Starting from
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| 100 | * other mean place systems, additional transformations will be
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| 101 | * needed; for example, FK4 (i.e. B1950) mean places would first
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| 102 | * have to be converted to FK5, which can be done with the
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| 103 | * palFk425 etc routines.
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| 104 | *
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| 105 | * - "Observed" Az,El means the position that would be seen by a
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| 106 | * perfect theodolite located at the observer. This is obtained
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| 107 | * from the geocentric apparent RA,Dec by allowing for Earth
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| 108 | * orientation and diurnal aberration, rotating from equator
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| 109 | * to horizon coordinates, and then adjusting for refraction.
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| 110 | * The HA,Dec is obtained by rotating back into equatorial
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| 111 | * coordinates, using the geodetic latitude corrected for polar
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| 112 | * motion, and is the position that would be seen by a perfect
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| 113 | * equatorial located at the observer and with its polar axis
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| 114 | * aligned to the Earth's axis of rotation (n.b. not to the
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| 115 | * refracted pole). Finally, the RA is obtained by subtracting
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| 116 | * the HA from the local apparent ST.
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| 117 | *
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| 118 | * - To predict the required setting of a real telescope, the
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| 119 | * observed place produced by this routine would have to be
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| 120 | * adjusted for the tilt of the azimuth or polar axis of the
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| 121 | * mounting (with appropriate corrections for mount flexures),
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| 122 | * for non-perpendicularity between the mounting axes, for the
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| 123 | * position of the rotator axis and the pointing axis relative
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| 124 | * to it, for tube flexure, for gear and encoder errors, and
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| 125 | * finally for encoder zero points. Some telescopes would, of
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| 126 | * course, exhibit other properties which would need to be
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| 127 | * accounted for at the appropriate point in the sequence.
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| 128 | *
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| 129 | * - This routine takes time to execute, due mainly to the
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| 130 | * rigorous integration used to evaluate the refraction.
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| 131 | * For processing multiple stars for one location and time,
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| 132 | * call palAoppa once followed by one call per star to palAopqk.
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| 133 | * Where a range of times within a limited period of a few hours
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| 134 | * is involved, and the highest precision is not required, call
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| 135 | * palAoppa once, followed by a call to palAoppat each time the
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| 136 | * time changes, followed by one call per star to palAopqk.
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| 137 | *
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| 138 | * - The DATE argument is UTC expressed as an MJD. This is,
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| 139 | * strictly speaking, wrong, because of leap seconds. However,
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| 140 | * as long as the delta UT and the UTC are consistent there
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| 141 | * are no difficulties, except during a leap second. In this
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| 142 | * case, the start of the 61st second of the final minute should
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| 143 | * begin a new MJD day and the old pre-leap delta UT should
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| 144 | * continue to be used. As the 61st second completes, the MJD
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| 145 | * should revert to the start of the day as, simultaneously,
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| 146 | * the delta UTC changes by one second to its post-leap new value.
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| 147 | *
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| 148 | * - The delta UT (UT1-UTC) is tabulated in IERS circulars and
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| 149 | * elsewhere. It increases by exactly one second at the end of
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| 150 | * each UTC leap second, introduced in order to keep delta UT
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| 151 | * within +/- 0.9 seconds.
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| 152 | *
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| 153 | * - IMPORTANT -- TAKE CARE WITH THE LONGITUDE SIGN CONVENTION.
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| 154 | * The longitude required by the present routine is east-positive,
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| 155 | * in accordance with geographical convention (and right-handed).
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| 156 | * In particular, note that the longitudes returned by the
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| 157 | * palObs routine are west-positive, following astronomical
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| 158 | * usage, and must be reversed in sign before use in the present
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| 159 | * routine.
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| 160 | *
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| 161 | * - The polar coordinates XP,YP can be obtained from IERS
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| 162 | * circulars and equivalent publications. The maximum amplitude
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| 163 | * is about 0.3 arcseconds. If XP,YP values are unavailable,
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| 164 | * use XP=YP=0.0. See page B60 of the 1988 Astronomical Almanac
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| 165 | * for a definition of the two angles.
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| 166 | *
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| 167 | * - The height above sea level of the observing station, HM,
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| 168 | * can be obtained from the Astronomical Almanac (Section J
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| 169 | * in the 1988 edition), or via the routine palObs. If P,
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| 170 | * the pressure in millibars, is available, an adequate
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| 171 | * estimate of HM can be obtained from the expression
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| 172 | *
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| 173 | * HM ~ -29.3*TSL*LOG(P/1013.25).
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| 174 | *
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| 175 | * where TSL is the approximate sea-level air temperature in K
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| 176 | * (see Astrophysical Quantities, C.W.Allen, 3rd edition,
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| 177 | * section 52). Similarly, if the pressure P is not known,
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| 178 | * it can be estimated from the height of the observing
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| 179 | * station, HM, as follows:
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| 180 | *
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| 181 | * P ~ 1013.25*EXP(-HM/(29.3*TSL)).
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| 182 | *
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| 183 | * Note, however, that the refraction is nearly proportional to the
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| 184 | * pressure and that an accurate P value is important for precise
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| 185 | * work.
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| 186 | *
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| 187 | * - The azimuths etc produced by the present routine are with
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| 188 | * respect to the celestial pole. Corrections to the terrestrial
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| 189 | * pole can be computed using palPolmo.
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| 190 |
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| 191 | * History:
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| 192 | * 2012-08-25 (TIMJ):
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| 193 | * Initial version
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| 194 | * Adapted with permission from the Fortran SLALIB library.
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| 195 | * {enter_further_changes_here}
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| 196 |
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| 197 | * Copyright:
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| 198 | * Copyright (C) 2005 Patrick T. Wallace
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| 199 | * Copyright (C) 2012 Science and Technology Facilities Council.
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| 200 | * All Rights Reserved.
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| 201 |
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| 202 | * Licence:
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| 203 | * This program is free software; you can redistribute it and/or
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| 204 | * modify it under the terms of the GNU General Public License as
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| 205 | * published by the Free Software Foundation; either version 3 of
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| 206 | * the License, or (at your option) any later version.
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| 207 | *
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| 208 | * This program is distributed in the hope that it will be
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| 209 | * useful, but WITHOUT ANY WARRANTY; without even the implied
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| 210 | * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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| 211 | * PURPOSE. See the GNU General Public License for more details.
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| 212 | *
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| 213 | * You should have received a copy of the GNU General Public License
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| 214 | * along with this program; if not, write to the Free Software
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| 215 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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| 216 | * MA 02110-1301, USA.
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| 217 |
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| 218 | * Bugs:
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| 219 | * {note_any_bugs_here}
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| 220 | *-
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| 221 | */
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| 222 |
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| 223 | #include "pal.h"
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| 224 |
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| 225 | void palAop ( double rap, double dap, double date, double dut,
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| 226 | double elongm, double phim, double hm, double xp,
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| 227 | double yp, double tdk, double pmb, double rh,
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| 228 | double wl, double tlr,
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| 229 | double *aob, double *zob, double *hob,
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| 230 | double *dob, double *rob ) {
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| 231 |
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| 232 | double aoprms[14];
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| 233 |
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| 234 | palAoppa(date,dut,elongm,phim,hm,xp,yp,tdk,pmb,rh,wl,tlr,
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| 235 | aoprms);
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| 236 | palAopqk(rap,dap,aoprms,aob,zob,hob,dob,rob);
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| 237 |
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| 238 | }
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