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C $Id: gdv.f 3304 2011-01-17 15:25:59Z brideout $
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C
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SUBROUTINE GDV(GDLAT,GCLAT,FR,FT,FP,FX,FY,FZ)
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C
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C jmh - 11/79 ans fortran 66
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C
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C GDV converts a vector field f at geodetic latitude GDLAT and
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C geocentric latitude GCLAT from a geocentric based representation
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C to a geodetic based representation. the geocentric components
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C are FR (radial outward), FT (increasing geocentric colatitude,
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C e.g. southward) and FP (increasing east longitude). the
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C geodetic components are FX (northward, parallel to surface of
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C earth), FY (eastward, parallel to surface of earth) and FZ
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C (downward, perpendicular to surface of earth). FR,FT,FP thus
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C correspond to spherical coordinates r,theta,phi, with their
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C origin at the center of the earth. x,y,z are the coordinates
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C customarily used to describe the three components of the
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C geomagnetic field. FP and FY are the same.
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C
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C Input:
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C GDLAT - geodetic latitude (degrees)
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C GCLAT - geocentric latitude (degrees)
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C FR - radial outward (geocentric).
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C FT - increasing geocentric colatitude (southward).
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C FP - increasing east longitude.
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C
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C Output:
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C FX - northward, parallel to surface of earth (geodetic).
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C FY - eastward, parallel to surface of earth.
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C FZ - downward, perpendicular to surface of earth.
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C
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C .. Scalar Arguments ..
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DOUBLE PRECISION FP,FR,FT,FX,FY,FZ,GCLAT,GDLAT
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C ..
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C .. Local Scalars ..
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DOUBLE PRECISION COSD,COSLAT,CT,DTR,GDL,SIND,SINLAT,ST,T
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C ..
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C .. Intrinsic Functions ..
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INTRINSIC DCOS,DSIN
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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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GDL = DTR*GDLAT
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SINLAT = DSIN(GDL)
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COSLAT = DCOS(GDL)
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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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SIND = ST*SINLAT - CT*COSLAT
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COSD = CT*SINLAT + ST*COSLAT
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FX = -FT*COSD - FR*SIND
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FY = FP
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FZ = FT*SIND - FR*COSD
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RETURN
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C
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END
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