diff options
Diffstat (limited to 'src/slalib/oap.f')
| -rw-r--r-- | src/slalib/oap.f | 172 |
1 files changed, 172 insertions, 0 deletions
diff --git a/src/slalib/oap.f b/src/slalib/oap.f new file mode 100644 index 0000000..6376397 --- /dev/null +++ b/src/slalib/oap.f @@ -0,0 +1,172 @@ + SUBROUTINE sla_OAP (TYPE, OB1, OB2, DATE, DUT, ELONGM, PHIM, + : HM, XP, YP, TDK, PMB, RH, WL, TLR, + : RAP, DAP) +*+ +* - - - - +* O A P +* - - - - +* +* Observed to apparent place +* +* Given: +* TYPE c*(*) type of coordinates - 'R', 'H' or 'A' (see below) +* OB1 d observed Az, HA or RA (radians; Az is N=0,E=90) +* OB2 d observed ZD or Dec (radians) +* DATE d UTC date/time (modified Julian Date, JD-2400000.5) +* DUT d delta UT: UT1-UTC (UTC seconds) +* ELONGM d mean longitude of the observer (radians, east +ve) +* PHIM d mean geodetic latitude of the observer (radians) +* HM d observer's height above sea level (metres) +* XP d polar motion x-coordinate (radians) +* YP d polar motion y-coordinate (radians) +* TDK d local ambient temperature (DegK; std=273.155D0) +* PMB d local atmospheric pressure (mB; std=1013.25D0) +* RH d local relative humidity (in the range 0D0-1D0) +* WL d effective wavelength (micron, e.g. 0.55D0) +* TLR d tropospheric lapse rate (DegK/metre, e.g. 0.0065D0) +* +* Returned: +* RAP d geocentric apparent right ascension +* DAP d geocentric apparent declination +* +* Notes: +* +* 1) Only the first character of the TYPE argument is significant. +* 'R' or 'r' indicates that OBS1 and OBS2 are the observed Right +* Ascension and Declination; 'H' or 'h' indicates that they are +* Hour Angle (West +ve) and Declination; anything else ('A' or +* 'a' is recommended) indicates that OBS1 and OBS2 are Azimuth +* (North zero, East is 90 deg) and zenith distance. (Zenith +* distance is used rather than elevation in order to reflect the +* fact that no allowance is made for depression of the horizon.) +* +* 2) The accuracy of the result is limited by the corrections for +* refraction. Providing the meteorological parameters are +* known accurately and there are no gross local effects, the +* predicted apparent RA,Dec should be within about 0.1 arcsec +* for a zenith distance of less than 70 degrees. Even at a +* topocentric zenith distance of 90 degrees, the accuracy in +* elevation should be better than 1 arcmin; useful results +* are available for a further 3 degrees, beyond which the +* sla_REFRO routine returns a fixed value of the refraction. +* The complementary routines sla_AOP (or sla_AOPQK) and sla_OAP +* (or sla_OAPQK) are self-consistent to better than 1 micro- +* arcsecond all over the celestial sphere. +* +* 3) It is advisable to take great care with units, as even +* unlikely values of the input parameters are accepted and +* processed in accordance with the models used. +* +* 4) "Observed" Az,El means the position that would be seen by a +* perfect theodolite located at the observer. This is +* related to the observed HA,Dec via the standard rotation, using +* the geodetic latitude (corrected for polar motion), while the +* observed HA and RA are related simply through the local +* apparent ST. "Observed" RA,Dec or HA,Dec thus means the +* position that would be seen by a perfect equatorial located +* at the observer and with its polar axis aligned to the +* Earth's axis of rotation (n.b. not to the refracted pole). +* By removing from the observed place the effects of +* atmospheric refraction and diurnal aberration, the +* geocentric apparent RA,Dec is obtained. +* +* 5) Frequently, mean rather than apparent RA,Dec will be required, +* in which case further transformations will be necessary. The +* sla_AMP etc routines will convert the apparent RA,Dec produced +* by the present routine into an "FK5" (J2000) mean place, by +* allowing for the Sun's gravitational lens effect, annual +* aberration, nutation and precession. Should "FK4" (1950) +* coordinates be needed, the routines sla_FK524 etc will also +* need to be applied. +* +* 6) To convert to apparent RA,Dec the coordinates read from a +* real telescope, corrections would have to be applied for +* encoder zero points, gear and encoder errors, tube flexure, +* the position of the rotator axis and the pointing axis +* relative to it, non-perpendicularity between the mounting +* axes, and finally for the tilt of the azimuth or polar axis +* of the mounting (with appropriate corrections for mount +* flexures). Some telescopes would, of course, exhibit other +* properties which would need to be accounted for at the +* appropriate point in the sequence. +* +* 7) The star-independent apparent-to-observed-place parameters +* in AOPRMS may be computed by means of the sla_AOPPA routine. +* If nothing has changed significantly except the time, the +* sla_AOPPAT routine may be used to perform the requisite +* partial recomputation of AOPRMS. +* +* 8) The DATE argument is UTC expressed as an MJD. This is, +* strictly speaking, wrong, because of leap seconds. However, +* as long as the delta UT and the UTC are consistent there +* are no difficulties, except during a leap second. In this +* case, the start of the 61st second of the final minute should +* begin a new MJD day and the old pre-leap delta UT should +* continue to be used. As the 61st second completes, the MJD +* should revert to the start of the day as, simultaneously, +* the delta UTC changes by one second to its post-leap new value. +* +* 9) The delta UT (UT1-UTC) is tabulated in IERS circulars and +* elsewhere. It increases by exactly one second at the end of +* each UTC leap second, introduced in order to keep delta UT +* within +/- 0.9 seconds. +* +* 10) IMPORTANT -- TAKE CARE WITH THE LONGITUDE SIGN CONVENTION. +* The longitude required by the present routine is east-positive, +* in accordance with geographical convention (and right-handed). +* In particular, note that the longitudes returned by the +* sla_OBS routine are west-positive, following astronomical +* usage, and must be reversed in sign before use in the present +* routine. +* +* 11) The polar coordinates XP,YP can be obtained from IERS +* circulars and equivalent publications. The maximum amplitude +* is about 0.3 arcseconds. If XP,YP values are unavailable, +* use XP=YP=0D0. See page B60 of the 1988 Astronomical Almanac +* for a definition of the two angles. +* +* 12) The height above sea level of the observing station, HM, +* can be obtained from the Astronomical Almanac (Section J +* in the 1988 edition), or via the routine sla_OBS. If P, +* the pressure in millibars, is available, an adequate +* estimate of HM can be obtained from the expression +* +* HM ~ -29.3D0*TSL*LOG(P/1013.25D0). +* +* where TSL is the approximate sea-level air temperature in +* deg K (see Astrophysical Quantities, C.W.Allen, 3rd edition, +* section 52). Similarly, if the pressure P is not known, +* it can be estimated from the height of the observing +* station, HM as follows: +* +* P ~ 1013.25D0*EXP(-HM/(29.3D0*TSL)). +* +* Note, however, that the refraction is proportional to the +* pressure and that an accurate P value is important for +* precise work. +* +* 13) The azimuths etc used by the present routine are with respect +* to the celestial pole. Corrections from the terrestrial pole +* can be computed using sla_POLMO. +* +* Called: sla_AOPPA, sla_OAPQK +* +* P.T.Wallace Starlink 6 September 1999 +* +* Copyright (C) 1999 P.T.Wallace and CCLRC +*- + + IMPLICIT NONE + + CHARACTER*(*) TYPE + DOUBLE PRECISION OB1,OB2,DATE,DUT,ELONGM,PHIM,HM, + : XP,YP,TDK,PMB,RH,WL,TLR,RAP,DAP + + DOUBLE PRECISION AOPRMS(14) + + + CALL sla_AOPPA(DATE,DUT,ELONGM,PHIM,HM,XP,YP,TDK,PMB,RH,WL,TLR, + : AOPRMS) + CALL sla_OAPQK(TYPE,OB1,OB2,AOPRMS,RAP,DAP) + + END |