| 1 | /*
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| 2 | *+
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| 3 | * Name:
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| 4 | * palOap
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| 5 |
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| 6 | * Purpose:
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| 7 | * Observed to apparent 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 palOap ( const char *type, double ob1, double ob2, double date,
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| 17 | * double dut, double elongm, double phim, double hm,
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| 18 | * double xp, double yp, double tdk, double pmb,
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| 19 | * double rh, double wl, double tlr,
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| 20 | * double *rap, double *dap );
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| 21 |
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| 22 | * Arguments:
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| 23 | * type = const char * (Given)
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| 24 | * Type of coordinates - 'R', 'H' or 'A' (see below)
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| 25 | * ob1 = double (Given)
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| 26 | * Observed Az, HA or RA (radians; Az is N=0;E=90)
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| 27 | * ob2 = double (Given)
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| 28 | * Observed ZD or Dec (radians)
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| 29 | * date = double (Given)
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| 30 | * UTC date/time (Modified Julian Date, JD-2400000.5)
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| 31 | * dut = double (Given)
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| 32 | * delta UT: UT1-UTC (UTC seconds)
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| 33 | * elongm = double (Given)
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| 34 | * Mean longitude of the observer (radians, east +ve)
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| 35 | * phim = double (Given)
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| 36 | * Mean geodetic latitude of the observer (radians)
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| 37 | * hm = double (Given)
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| 38 | * Observer's height above sea level (metres)
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| 39 | * xp = double (Given)
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| 40 | * Polar motion x-coordinates (radians)
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| 41 | * yp = double (Given)
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| 42 | * Polar motion y-coordinates (radians)
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| 43 | * tdk = double (Given)
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| 44 | * Local ambient temperature (K; std=273.15)
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| 45 | * pmb = double (Given)
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| 46 | * Local atmospheric pressure (mb; std=1013.25)
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| 47 | * rh = double (Given)
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| 48 | * Local relative humidity (in the range 0.0-1.0)
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| 49 | * wl = double (Given)
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| 50 | * Effective wavelength (micron, e.g. 0.55)
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| 51 | * tlr = double (Given)
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| 52 | * Tropospheric laps rate (K/metre, e.g. 0.0065)
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| 53 | * rap = double * (Given)
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| 54 | * Geocentric apparent right ascension
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| 55 | * dap = double * (Given)
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| 56 | * Geocentric apparent declination
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| 57 |
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| 58 | * Description:
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| 59 | * Observed to apparent place.
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| 60 |
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| 61 | * Authors:
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| 62 | * PTW: Patrick T. Wallace
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| 63 | * TIMJ: Tim Jenness (JAC, Hawaii)
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| 64 | * {enter_new_authors_here}
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| 65 |
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| 66 | * Notes:
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| 67 | * - Only the first character of the TYPE argument is significant.
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| 68 | * 'R' or 'r' indicates that OBS1 and OBS2 are the observed right
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| 69 | * ascension and declination; 'H' or 'h' indicates that they are
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| 70 | * hour angle (west +ve) and declination; anything else ('A' or
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| 71 | * 'a' is recommended) indicates that OBS1 and OBS2 are azimuth
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| 72 | * (north zero, east 90 deg) and zenith distance. (Zenith
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| 73 | * distance is used rather than elevation in order to reflect the
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| 74 | * fact that no allowance is made for depression of the horizon.)
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| 75 | *
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| 76 | * - The accuracy of the result is limited by the corrections for
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| 77 | * refraction. Providing the meteorological parameters are
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| 78 | * known accurately and there are no gross local effects, the
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| 79 | * predicted apparent RA,Dec should be within about 0.1 arcsec
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| 80 | * for a zenith distance of less than 70 degrees. Even at a
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| 81 | * topocentric zenith distance of 90 degrees, the accuracy in
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| 82 | * elevation should be better than 1 arcmin; useful results
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| 83 | * are available for a further 3 degrees, beyond which the
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| 84 | * palRefro routine returns a fixed value of the refraction.
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| 85 | * The complementary routines palAop (or palAopqk) and palOap
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| 86 | * (or palOapqk) are self-consistent to better than 1 micro-
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| 87 | * arcsecond all over the celestial sphere.
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| 88 | *
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| 89 | * - It is advisable to take great care with units, as even
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| 90 | * unlikely values of the input parameters are accepted and
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| 91 | * processed in accordance with the models used.
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| 92 | *
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| 93 | * - "Observed" Az,El means the position that would be seen by a
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| 94 | * perfect theodolite located at the observer. This is
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| 95 | * related to the observed HA,Dec via the standard rotation, using
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| 96 | * the geodetic latitude (corrected for polar motion), while the
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| 97 | * observed HA and RA are related simply through the local
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| 98 | * apparent ST. "Observed" RA,Dec or HA,Dec thus means the
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| 99 | * position that would be seen by a perfect equatorial located
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| 100 | * at the observer and with its polar axis aligned to the
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| 101 | * Earth's axis of rotation (n.b. not to the refracted pole).
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| 102 | * By removing from the observed place the effects of
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| 103 | * atmospheric refraction and diurnal aberration, the
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| 104 | * geocentric apparent RA,Dec is obtained.
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| 105 | *
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| 106 | * - Frequently, mean rather than apparent RA,Dec will be required,
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| 107 | * in which case further transformations will be necessary. The
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| 108 | * palAmp etc routines will convert the apparent RA,Dec produced
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| 109 | * by the present routine into an "FK5" (J2000) mean place, by
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| 110 | * allowing for the Sun's gravitational lens effect, annual
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| 111 | * aberration, nutation and precession. Should "FK4" (1950)
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| 112 | * coordinates be needed, the routines palFk524 etc will also
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| 113 | * need to be applied.
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| 114 | *
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| 115 | * - To convert to apparent RA,Dec the coordinates read from a
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| 116 | * real telescope, corrections would have to be applied for
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| 117 | * encoder zero points, gear and encoder errors, tube flexure,
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| 118 | * the position of the rotator axis and the pointing axis
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| 119 | * relative to it, non-perpendicularity between the mounting
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| 120 | * axes, and finally for the tilt of the azimuth or polar axis
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| 121 | * of the mounting (with appropriate corrections for mount
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| 122 | * flexures). Some telescopes would, of course, exhibit other
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| 123 | * properties which would need to be accounted for at the
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| 124 | * appropriate point in the sequence.
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| 125 | *
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| 126 | * - This routine takes time to execute, due mainly to the rigorous
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| 127 | * integration used to evaluate the refraction. For processing
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| 128 | * multiple stars for one location and time, call palAoppa once
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| 129 | * followed by one call per star to palOapqk. Where a range of
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| 130 | * times within a limited period of a few hours is involved, and the
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| 131 | * highest precision is not required, call palAoppa once, followed
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| 132 | * by a call to palAoppat each time the time changes, followed by
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| 133 | * one call per star to palOapqk.
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| 134 | *
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| 135 | * - The DATE argument is UTC expressed as an MJD. This is, strictly
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| 136 | * speaking, wrong, because of leap seconds. However, as long as
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| 137 | * the delta UT and the UTC are consistent there are no
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| 138 | * difficulties, except during a leap second. In this case, the
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| 139 | * start of the 61st second of the final minute should begin a new
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| 140 | * MJD day and the old pre-leap delta UT should continue to be used.
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| 141 | * As the 61st second completes, the MJD should revert to the start
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| 142 | * of the day as, simultaneously, the delta UTC changes by one
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| 143 | * second to its post-leap new value.
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| 144 | *
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| 145 | * - The delta UT (UT1-UTC) is tabulated in IERS circulars and
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| 146 | * elsewhere. It increases by exactly one second at the end of
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| 147 | * each UTC leap second, introduced in order to keep delta UT
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| 148 | * within +/- 0.9 seconds.
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| 149 | *
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| 150 | * - IMPORTANT -- TAKE CARE WITH THE LONGITUDE SIGN CONVENTION.
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| 151 | * The longitude required by the present routine is east-positive,
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| 152 | * in accordance with geographical convention (and right-handed).
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| 153 | * In particular, note that the longitudes returned by the
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| 154 | * palOBS routine are west-positive, following astronomical
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| 155 | * usage, and must be reversed in sign before use in the present
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| 156 | * routine.
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| 157 | *
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| 158 | * - The polar coordinates XP,YP can be obtained from IERS
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| 159 | * circulars and equivalent publications. The maximum amplitude
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| 160 | * is about 0.3 arcseconds. If XP,YP values are unavailable,
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| 161 | * use XP=YP=0D0. See page B60 of the 1988 Astronomical Almanac
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| 162 | * for a definition of the two angles.
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| 163 | *
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| 164 | * - The height above sea level of the observing station, HM,
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| 165 | * can be obtained from the Astronomical Almanac (Section J
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| 166 | * in the 1988 edition), or via the routine palOBS. If P,
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| 167 | * the pressure in millibars, is available, an adequate
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| 168 | * estimate of HM can be obtained from the expression
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| 169 | *
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| 170 | * HM ~ -29.3*TSL*LOG(P/1013.25).
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| 171 | *
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| 172 | * where TSL is the approximate sea-level air temperature in K
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| 173 | * (see Astrophysical Quantities, C.W.Allen, 3rd edition,
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| 174 | * section 52). Similarly, if the pressure P is not known,
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| 175 | * it can be estimated from the height of the observing
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| 176 | * station, HM, as follows:
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| 177 | *
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| 178 | * P ~ 1013.25*EXP(-HM/(29.3*TSL)).
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| 179 | *
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| 180 | * Note, however, that the refraction is nearly proportional to the
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| 181 | * pressure and that an accurate P value is important for precise
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| 182 | * work.
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| 183 | *
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| 184 | * - The azimuths etc. used by the present routine are with respect
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| 185 | * to the celestial pole. Corrections from the terrestrial pole
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| 186 | * can be computed using palPolmo.
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| 187 |
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| 188 | * History:
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| 189 | * 2012-08-27 (TIMJ):
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| 190 | * Initial version, copied from Fortran SLA
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| 191 | * Adapted with permission from the Fortran SLALIB library.
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| 192 | * {enter_further_changes_here}
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| 193 |
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| 194 | * Copyright:
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| 195 | * Copyright (C) 2005 Patrick T. Wallace
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| 196 | * Copyright (C) 2012 Science and Technology Facilities Council.
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| 197 | * All Rights Reserved.
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| 198 |
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| 199 | * Licence:
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| 200 | * This program is free software; you can redistribute it and/or
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| 201 | * modify it under the terms of the GNU General Public License as
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| 202 | * published by the Free Software Foundation; either version 3 of
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| 203 | * the License, or (at your option) any later version.
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| 204 | *
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| 205 | * This program is distributed in the hope that it will be
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| 206 | * useful, but WITHOUT ANY WARRANTY; without even the implied
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| 207 | * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
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| 208 | * PURPOSE. See the GNU General Public License for more details.
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| 209 | *
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| 210 | * You should have received a copy of the GNU General Public License
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| 211 | * along with this program; if not, write to the Free Software
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| 212 | * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
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| 213 | * MA 02110-1301, USA.
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| 214 |
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| 215 | * Bugs:
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| 216 | * {note_any_bugs_here}
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| 217 | *-
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| 218 | */
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| 219 |
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| 220 | #include "pal.h"
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| 221 |
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| 222 | void palOap ( const char *type, double ob1, double ob2, double date,
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| 223 | double dut, double elongm, double phim, double hm,
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| 224 | double xp, double yp, double tdk, double pmb,
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| 225 | double rh, double wl, double tlr,
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| 226 | double *rap, double *dap ) {
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| 227 |
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| 228 | double aoprms[14];
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| 229 |
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| 230 | palAoppa(date,dut,elongm,phim,hm,xp,yp,tdk,pmb,rh,wl,tlr,
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| 231 | aoprms);
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| 232 | palOapqk(type,ob1,ob2,aoprms,rap,dap);
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| 233 |
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| 234 | }
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