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Diffstat (limited to 'src/slalib/altaz.f')
| -rw-r--r-- | src/slalib/altaz.f | 145 |
1 files changed, 145 insertions, 0 deletions
diff --git a/src/slalib/altaz.f b/src/slalib/altaz.f new file mode 100644 index 0000000..3a7124b --- /dev/null +++ b/src/slalib/altaz.f @@ -0,0 +1,145 @@ + SUBROUTINE sla_ALTAZ (HA, DEC, PHI, + : AZ, AZD, AZDD, EL, ELD, ELDD, PA, PAD, PADD) +*+ +* - - - - - - +* A L T A Z +* - - - - - - +* +* Positions, velocities and accelerations for an altazimuth +* telescope mount. +* +* (double precision) +* +* Given: +* HA d hour angle +* DEC d declination +* PHI d observatory latitude +* +* Returned: +* AZ d azimuth +* AZD d " velocity +* AZDD d " acceleration +* EL d elevation +* ELD d " velocity +* ELDD d " acceleration +* PA d parallactic angle +* PAD d " " velocity +* PADD d " " acceleration +* +* Notes: +* +* 1) Natural units are used throughout. HA, DEC, PHI, AZ, EL +* and ZD are in radians. The velocities and accelerations +* assume constant declination and constant rate of change of +* hour angle (as for tracking a star); the units of AZD, ELD +* and PAD are radians per radian of HA, while the units of AZDD, +* ELDD and PADD are radians per radian of HA squared. To +* convert into practical degree- and second-based units: +* +* angles * 360/2pi -> degrees +* velocities * (2pi/86400)*(360/2pi) -> degree/sec +* accelerations * ((2pi/86400)**2)*(360/2pi) -> degree/sec/sec +* +* Note that the seconds here are sidereal rather than SI. One +* sidereal second is about 0.99727 SI seconds. +* +* The velocity and acceleration factors assume the sidereal +* tracking case. Their respective numerical values are (exactly) +* 1/240 and (approximately) 1/3300236.9. +* +* 2) Azimuth is returned in the range 0-2pi; north is zero, +* and east is +pi/2. Elevation and parallactic angle are +* returned in the range +/-pi/2. Position angle is +ve +* for a star west of the meridian and is the angle NP-star-zenith. +* +* 3) The latitude is geodetic as opposed to geocentric. The +* hour angle and declination are topocentric. Refraction and +* deficiencies in the telescope mounting are ignored. The +* purpose of the routine is to give the general form of the +* quantities. The details of a real telescope could profoundly +* change the results, especially close to the zenith. +* +* 4) No range checking of arguments is carried out. +* +* 5) In applications which involve many such calculations, rather +* than calling the present routine it will be more efficient to +* use inline code, having previously computed fixed terms such +* as sine and cosine of latitude, and (for tracking a star) +* sine and cosine of declination. +* +* P.T.Wallace Starlink 14 March 1997 +* +* Copyright (C) 1997 Rutherford Appleton Laboratory +*- + + IMPLICIT NONE + + DOUBLE PRECISION HA,DEC,PHI,AZ,AZD,AZDD,EL,ELD,ELDD,PA,PAD,PADD + + DOUBLE PRECISION DPI,D2PI,TINY + PARAMETER (DPI=3.1415926535897932384626433832795D0, + : D2PI=6.283185307179586476925286766559D0, + : TINY=1D-30) + + DOUBLE PRECISION SH,CH,SD,CD,SP,CP,CHCD,SDCP,X,Y,Z,RSQ,R,A,E,C,S, + : Q,QD,AD,ED,EDR,ADD,EDD,QDD + + +* Useful functions + SH=SIN(HA) + CH=COS(HA) + SD=SIN(DEC) + CD=COS(DEC) + SP=SIN(PHI) + CP=COS(PHI) + CHCD=CH*CD + SDCP=SD*CP + X=-CHCD*SP+SDCP + Y=-SH*CD + Z=CHCD*CP+SD*SP + RSQ=X*X+Y*Y + R=SQRT(RSQ) + +* Azimuth and elevation + IF (RSQ.EQ.0D0) THEN + A=0D0 + ELSE + A=ATAN2(Y,X) + END IF + IF (A.LT.0D0) A=A+D2PI + E=ATAN2(Z,R) + +* Parallactic angle + C=CD*SP-CH*SDCP + S=SH*CP + IF (C*C+S*S.GT.0) THEN + Q=ATAN2(S,C) + ELSE + Q=DPI-HA + END IF + +* Velocities and accelerations (clamped at zenith/nadir) + IF (RSQ.LT.TINY) THEN + RSQ=TINY + R=SQRT(RSQ) + END IF + QD=-X*CP/RSQ + AD=SP+Z*QD + ED=CP*Y/R + EDR=ED/R + ADD=EDR*(Z*SP+(2D0-RSQ)*QD) + EDD=-R*QD*AD + QDD=EDR*(SP+2D0*Z*QD) + +* Results + AZ=A + AZD=AD + AZDD=ADD + EL=E + ELD=ED + ELDD=EDD + PA=Q + PAD=QD + PADD=QDD + + END |