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C $Id: gdmag.f 3304 2011-01-17 15:25:59Z brideout $
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C
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SUBROUTINE GDMAG(TM,GDLAT,GLON,GDALT,X,Y,Z,F,H,DEC,AINC)
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C
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C jmh - 1/80 ans fortran 66
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C
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C Evaluates the geomagnetic field at a point specified by its
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C geodetic coordinates. the reference geoid is that adopted by the
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C iau in 1964.
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C
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C input:
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C TM - time in years for desired field (e.g. 1971.25)
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C GDLAT - geodetic latitude (degrees)
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C GLON - east longitude (degrees)
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C GDALT - altitude above geoid (km)
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C
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C output:
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C X,Y,Z - geodetic field components (gauss)
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C F - magnitude of field (gauss)
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C H - horizontal intensity (gauss)
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C DEC - declination (degrees)
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C AINC - inclination (degrees)
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C
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C .. Scalar Arguments ..
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DOUBLE PRECISION AINC,DEC,F,GDALT,GDLAT,GLON,H,TM,X,Y,Z
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C ..
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C .. Local Scalars ..
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DOUBLE PRECISION BP,BR,BT,CP,CT,DTR,GCLAT,P,RKM,SP,ST,T
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C ..
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C .. External Subroutines ..
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EXTERNAL CONVRT,GDV,MILMAG
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C ..
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C .. Intrinsic Functions ..
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INTRINSIC DATAN2,DCOS,DSIN,DSQRT
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C ..
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C .. Data statements ..
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DATA DTR/.0174532925199D0/
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C ..
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C
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CALL CONVRT(1,GDLAT,GDALT,GCLAT,RKM)
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T = DTR*(90.D0-GCLAT)
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CT = DCOS(T)
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ST = DSIN(T)
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P = DTR*GLON
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CP = DCOS(P)
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SP = DSIN(P)
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CALL MILMAG(TM,RKM,ST,CT,SP,CP,BR,BT,BP,F)
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CALL GDV(GDLAT,GCLAT,BR,BT,BP,X,Y,Z)
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H = DSQRT(X*X+Y*Y)
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DEC = DATAN2(Y,X)/DTR
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AINC = DATAN2(Z,H)/DTR
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RETURN
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C
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END
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