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193 lines
8.9 KiB
Fortran
193 lines
8.9 KiB
Fortran
SUBROUTINE sla_OAP ( TYPE, OB1, OB2, DATE, DUT, ELONGM, PHIM,
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: HM, XP, YP, TDK, PMB, RH, WL, TLR,
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: RAP, DAP )
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*+
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* - - - -
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* O A P
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* - - - -
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*
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* Observed to apparent place.
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*
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* Given:
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* TYPE c*(*) type of coordinates - 'R', 'H' or 'A' (see below)
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* OB1 d observed Az, HA or RA (radians; Az is N=0,E=90)
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* OB2 d observed ZD or Dec (radians)
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* DATE d UTC date/time (modified Julian Date, JD-2400000.5)
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* DUT d delta UT: UT1-UTC (UTC seconds)
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* ELONGM d mean longitude of the observer (radians, east +ve)
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* PHIM d mean geodetic latitude of the observer (radians)
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* HM d observer's height above sea level (metres)
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* XP d polar motion x-coordinate (radians)
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* YP d polar motion y-coordinate (radians)
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* TDK d local ambient temperature (K; std=273.15D0)
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* PMB d local atmospheric pressure (mb; std=1013.25D0)
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* RH d local relative humidity (in the range 0D0-1D0)
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* WL d effective wavelength (micron, e.g. 0.55D0)
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* TLR d tropospheric lapse rate (K/metre, e.g. 0.0065D0)
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*
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* Returned:
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* RAP d geocentric apparent right ascension
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* DAP d geocentric apparent declination
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*
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* Notes:
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*
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* 1) Only the first character of the TYPE argument is significant.
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* 'R' or 'r' indicates that OBS1 and OBS2 are the observed right
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* ascension and declination; 'H' or 'h' indicates that they are
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* hour angle (west +ve) and declination; anything else ('A' or
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* 'a' is recommended) indicates that OBS1 and OBS2 are azimuth
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* (north zero, east 90 deg) and zenith distance. (Zenith
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* distance is used rather than elevation in order to reflect the
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* fact that no allowance is made for depression of the horizon.)
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*
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* 2) The accuracy of the result is limited by the corrections for
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* refraction. Providing the meteorological parameters are
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* known accurately and there are no gross local effects, the
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* predicted apparent RA,Dec should be within about 0.1 arcsec
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* for a zenith distance of less than 70 degrees. Even at a
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* topocentric zenith distance of 90 degrees, the accuracy in
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* elevation should be better than 1 arcmin; useful results
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* are available for a further 3 degrees, beyond which the
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* sla_REFRO routine returns a fixed value of the refraction.
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* The complementary routines sla_AOP (or sla_AOPQK) and sla_OAP
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* (or sla_OAPQK) are self-consistent to better than 1 micro-
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* arcsecond all over the celestial sphere.
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*
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* 3) It is advisable to take great care with units, as even
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* unlikely values of the input parameters are accepted and
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* processed in accordance with the models used.
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*
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* 4) "Observed" Az,El means the position that would be seen by a
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* perfect theodolite located at the observer. This is
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* related to the observed HA,Dec via the standard rotation, using
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* the geodetic latitude (corrected for polar motion), while the
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* observed HA and RA are related simply through the local
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* apparent ST. "Observed" RA,Dec or HA,Dec thus means the
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* position that would be seen by a perfect equatorial located
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* at the observer and with its polar axis aligned to the
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* Earth's axis of rotation (n.b. not to the refracted pole).
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* By removing from the observed place the effects of
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* atmospheric refraction and diurnal aberration, the
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* geocentric apparent RA,Dec is obtained.
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*
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* 5) Frequently, mean rather than apparent RA,Dec will be required,
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* in which case further transformations will be necessary. The
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* sla_AMP etc routines will convert the apparent RA,Dec produced
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* by the present routine into an "FK5" (J2000) mean place, by
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* allowing for the Sun's gravitational lens effect, annual
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* aberration, nutation and precession. Should "FK4" (1950)
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* coordinates be needed, the routines sla_FK524 etc will also
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* need to be applied.
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*
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* 6) To convert to apparent RA,Dec the coordinates read from a
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* real telescope, corrections would have to be applied for
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* encoder zero points, gear and encoder errors, tube flexure,
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* the position of the rotator axis and the pointing axis
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* relative to it, non-perpendicularity between the mounting
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* axes, and finally for the tilt of the azimuth or polar axis
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* of the mounting (with appropriate corrections for mount
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* flexures). Some telescopes would, of course, exhibit other
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* properties which would need to be accounted for at the
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* appropriate point in the sequence.
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*
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* 7) This routine takes time to execute, due mainly to the rigorous
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* integration used to evaluate the refraction. For processing
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* multiple stars for one location and time, call sla_AOPPA once
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* followed by one call per star to sla_OAPQK. Where a range of
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* times within a limited period of a few hours is involved, and the
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* highest precision is not required, call sla_AOPPA once, followed
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* by a call to sla_AOPPAT each time the time changes, followed by
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* one call per star to sla_OAPQK.
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*
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* 8) The DATE argument is UTC expressed as an MJD. This is, strictly
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* speaking, wrong, because of leap seconds. However, as long as
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* the delta UT and the UTC are consistent there are no
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* difficulties, except during a leap second. In this case, the
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* start of the 61st second of the final minute should begin a new
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* MJD day and the old pre-leap delta UT should continue to be used.
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* As the 61st second completes, the MJD should revert to the start
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* of the day as, simultaneously, the delta UTC changes by one
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* second to its post-leap new value.
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*
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* 9) The delta UT (UT1-UTC) is tabulated in IERS circulars and
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* elsewhere. It increases by exactly one second at the end of
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* each UTC leap second, introduced in order to keep delta UT
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* within +/- 0.9 seconds.
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*
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* 10) IMPORTANT -- TAKE CARE WITH THE LONGITUDE SIGN CONVENTION.
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* The longitude required by the present routine is east-positive,
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* in accordance with geographical convention (and right-handed).
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* In particular, note that the longitudes returned by the
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* sla_OBS routine are west-positive, following astronomical
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* usage, and must be reversed in sign before use in the present
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* routine.
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*
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* 11) The polar coordinates XP,YP can be obtained from IERS
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* circulars and equivalent publications. The maximum amplitude
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* is about 0.3 arcseconds. If XP,YP values are unavailable,
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* use XP=YP=0D0. See page B60 of the 1988 Astronomical Almanac
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* for a definition of the two angles.
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*
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* 12) The height above sea level of the observing station, HM,
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* can be obtained from the Astronomical Almanac (Section J
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* in the 1988 edition), or via the routine sla_OBS. If P,
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* the pressure in millibars, is available, an adequate
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* estimate of HM can be obtained from the expression
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*
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* HM ~ -29.3D0*TSL*LOG(P/1013.25D0).
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*
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* where TSL is the approximate sea-level air temperature in K
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* (see Astrophysical Quantities, C.W.Allen, 3rd edition,
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* section 52). Similarly, if the pressure P is not known,
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* it can be estimated from the height of the observing
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* station, HM, as follows:
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*
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* P ~ 1013.25D0*EXP(-HM/(29.3D0*TSL)).
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*
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* Note, however, that the refraction is nearly proportional to the
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* pressure and that an accurate P value is important for precise
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* work.
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*
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* 13) The azimuths etc. used by the present routine are with respect
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* to the celestial pole. Corrections from the terrestrial pole
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* can be computed using sla_POLMO.
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*
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* Called: sla_AOPPA, sla_OAPQK
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*
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* Last revision: 2 December 2005
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*
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* Copyright P.T.Wallace. All rights reserved.
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*
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* License:
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program (see SLA_CONDITIONS); if not, write to the
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* Free Software Foundation, Inc., 59 Temple Place, Suite 330,
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* Boston, MA 02111-1307 USA
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*
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*-
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IMPLICIT NONE
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CHARACTER*(*) TYPE
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DOUBLE PRECISION OB1,OB2,DATE,DUT,ELONGM,PHIM,HM,
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: XP,YP,TDK,PMB,RH,WL,TLR,RAP,DAP
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DOUBLE PRECISION AOPRMS(14)
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CALL sla_AOPPA(DATE,DUT,ELONGM,PHIM,HM,XP,YP,TDK,PMB,RH,WL,TLR,
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: AOPRMS)
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CALL sla_OAPQK(TYPE,OB1,OB2,AOPRMS,RAP,DAP)
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END
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