2007-01-11 21:25:52 +00:00
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subroutine geodist(Eplat, Eplon, Stlat, Stlon,
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+ Az, Baz, Dist)
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implicit none
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real eplat, eplon, stlat, stlon, az, baz, dist
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C JHT: In actual fact, I use the first two arguments for "My Location",
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C the second two for "His location"; West longitude is positive.
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c
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c
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c Taken directly from:
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c Thomas, P.D., 1970, Spheroidal geodesics, reference systems,
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c & local geometry, U.S. Naval Oceanographic Office SP-138,
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c 165 pp.
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c
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c assumes North Latitude and East Longitude are positive
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c
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c EpLat, EpLon = End point Lat/Long
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c Stlat, Stlon = Start point lat/long
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c Az, BAz = direct & reverse azimuith
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c Dist = Dist (km); Deg = central angle, discarded
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c
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real BOA, F, P1R, P2R, L1R, L2R, DLR, T1R, T2R, TM,
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+ DTM, STM, CTM, SDTM,CDTM, KL, KK, SDLMR, L,
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+ CD, DL, SD, T, U, V, D, X, E, Y, A, FF64, TDLPM,
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+ HAPBR, HAMBR, A1M2, A2M1
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real AL,BL,D2R,Pi2
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data AL/6378206.4/ ! Clarke 1866 ellipsoid
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data BL/6356583.8/
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c real pi /3.14159265359/
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data D2R/0.01745329251994/ ! degrees to radians conversion factor
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data Pi2/6.28318530718/
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BOA = BL/AL
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F = 1.0 - BOA
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c convert st/end pts to radians
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P1R = Eplat * D2R
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P2R = Stlat * D2R
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L1R = Eplon * D2R
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L2R = StLon * D2R
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DLR = L2R - L1R ! DLR = Delta Long in Rads
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T1R = ATan(BOA * Tan(P1R))
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T2R = ATan(BOA * Tan(P2R))
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TM = (T1R + T2R) / 2.0
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DTM = (T2R - T1R) / 2.0
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STM = Sin(TM)
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CTM = Cos(TM)
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SDTM = Sin(DTM)
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CDTM = Cos(DTM)
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KL = STM * CDTM
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KK = SDTM * CTM
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SDLMR = Sin(DLR/2.0)
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L = SDTM * SDTM + SDLMR * SDLMR * (CDTM * CDTM - STM * STM)
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CD = 1.0 - 2.0 * L
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DL = ACos(CD)
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SD = Sin(DL)
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T = DL/SD
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U = 2.0 * KL * KL / (1.0 - L)
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V = 2.0 * KK * KK / L
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D = 4.0 * T * T
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X = U + V
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E = -2.0 * CD
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Y = U - V
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A = -D * E
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FF64 = F * F / 64.0
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Dist = AL*SD*(T -(F/4.0)*(T*X-Y)+FF64*(X*(A+(T-(A+E)
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+ /2.0)*X)+Y*(-2.0*D+E*Y)+D*X*Y))/1000.0
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TDLPM = Tan((DLR+(-((E*(4.0-X)+2.0*Y)*((F/2.0)*T+FF64*
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+ (32.0*T+(A-20.0*T)*X-2.0*(D+2.0)*Y))/4.0)*Tan(DLR)))/2.0)
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HAPBR = ATan2(SDTM,(CTM*TDLPM))
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HAMBR = Atan2(CDTM,(STM*TDLPM))
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A1M2 = Pi2 + HAMBR - HAPBR
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A2M1 = Pi2 - HAMBR - HAPBR
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1 If ((A1M2 .ge. 0.0) .AND. (A1M2 .lt. Pi2)) GOTO 5
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If (A1M2 .lt. Pi2) GOTO 4
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A1M2 = A1M2 - Pi2
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GOTO 1
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4 A1M2 = A1M2 + Pi2
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GOTO 1
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c
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c all of this gens the proper az, baz (forward and back azimuth)
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c
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5 If ((A2M1 .ge. 0.0) .AND. (A2M1 .lt. Pi2)) GOTO 9
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If (A2M1 .lt. Pi2) GOTO 8
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A2M1 = A2M1 - Pi2
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GOTO 5
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8 A2M1 = A2M1 + Pi2
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GOTO 5
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9 Az = A1M2 / D2R
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BAZ = A2M1 / D2R
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c
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c Fix the mirrored coords here.
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c
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az = 360.0 - az
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baz = 360.0 - baz
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end
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