mirror of
https://github.com/pavel-demin/ft8d.git
synced 2024-11-14 16:11:48 -05:00
106 lines
2.8 KiB
Fortran
106 lines
2.8 KiB
Fortran
subroutine geodist(Eplat,Eplon,Stlat,Stlon,Az,Baz,Dist)
|
|
implicit none
|
|
real eplat, eplon, stlat, stlon, az, baz, dist
|
|
|
|
! JHT: In actual fact, I use the first two arguments for "My Location",
|
|
! the second two for "His location"; West longitude is positive.
|
|
|
|
! Taken directly from:
|
|
! Thomas, P.D., 1970, Spheroidal geodesics, reference systems,
|
|
! & local geometry, U.S. Naval Oceanographi!Office SP-138,
|
|
! 165 pp.
|
|
! assumes North Latitude and East Longitude are positive
|
|
|
|
! EpLat, EpLon = End point Lat/Long
|
|
! Stlat, Stlon = Start point lat/long
|
|
! Az, BAz = direct & reverse azimuith
|
|
! Dist = Dist (km); Deg = central angle, discarded
|
|
|
|
real BOA, F, P1R, P2R, L1R, L2R, DLR, T1R, T2R, TM, &
|
|
DTM, STM, CTM, SDTM,CDTM, KL, KK, SDLMR, L, &
|
|
CD, DL, SD, T, U, V, D, X, E, Y, A, FF64, TDLPM, &
|
|
HAPBR, HAMBR, A1M2, A2M1
|
|
|
|
real AL,BL,D2R,Pi2
|
|
|
|
data AL/6378206.4/ ! Clarke 1866 ellipsoid
|
|
data BL/6356583.8/
|
|
! real pi /3.14159265359/
|
|
data D2R/0.01745329251994/ ! degrees to radians conversion factor
|
|
data Pi2/6.28318530718/
|
|
|
|
if(abs(Eplat-Stlat).lt.0.02 .and. abs(Eplon-Stlon).lt.0.02) then
|
|
Az=0.
|
|
Baz=180.0
|
|
Dist=0
|
|
go to 999
|
|
endif
|
|
|
|
BOA = BL/AL
|
|
F = 1.0 - BOA
|
|
! Convert st/end pts to radians
|
|
P1R = Eplat * D2R
|
|
P2R = Stlat * D2R
|
|
L1R = Eplon * D2R
|
|
L2R = StLon * D2R
|
|
DLR = L2R - L1R ! DLR = Delta Long in Rads
|
|
T1R = ATan(BOA * Tan(P1R))
|
|
T2R = ATan(BOA * Tan(P2R))
|
|
TM = (T1R + T2R) / 2.0
|
|
DTM = (T2R - T1R) / 2.0
|
|
STM = Sin(TM)
|
|
CTM = Cos(TM)
|
|
SDTM = Sin(DTM)
|
|
CDTM = Cos(DTM)
|
|
KL = STM * CDTM
|
|
KK = SDTM * CTM
|
|
SDLMR = Sin(DLR/2.0)
|
|
L = SDTM * SDTM + SDLMR * SDLMR * (CDTM * CDTM - STM * STM)
|
|
CD = 1.0 - 2.0 * L
|
|
DL = ACos(CD)
|
|
SD = Sin(DL)
|
|
T = DL/SD
|
|
U = 2.0 * KL * KL / (1.0 - L)
|
|
V = 2.0 * KK * KK / L
|
|
D = 4.0 * T * T
|
|
X = U + V
|
|
E = -2.0 * CD
|
|
Y = U - V
|
|
A = -D * E
|
|
FF64 = F * F / 64.0
|
|
Dist = AL*SD*(T -(F/4.0)*(T*X-Y)+FF64*(X*(A+(T-(A+E) &
|
|
/2.0)*X)+Y*(-2.0*D+E*Y)+D*X*Y))/1000.0
|
|
TDLPM = Tan((DLR+(-((E*(4.0-X)+2.0*Y)*((F/2.0)*T+FF64* &
|
|
(32.0*T+(A-20.0*T)*X-2.0*(D+2.0)*Y))/4.0)*Tan(DLR)))/2.0)
|
|
HAPBR = ATan2(SDTM,(CTM*TDLPM))
|
|
HAMBR = Atan2(CDTM,(STM*TDLPM))
|
|
A1M2 = Pi2 + HAMBR - HAPBR
|
|
A2M1 = Pi2 - HAMBR - HAPBR
|
|
|
|
1 If ((A1M2 .ge. 0.0) .AND. (A1M2 .lt. Pi2)) GOTO 5
|
|
If (A1M2 .lt. Pi2) GOTO 4
|
|
A1M2 = A1M2 - Pi2
|
|
GOTO 1
|
|
4 A1M2 = A1M2 + Pi2
|
|
GOTO 1
|
|
|
|
! All of this gens the proper az, baz (forward and back azimuth)
|
|
|
|
5 If ((A2M1 .ge. 0.0) .AND. (A2M1 .lt. Pi2)) GOTO 9
|
|
If (A2M1 .lt. Pi2) GOTO 8
|
|
A2M1 = A2M1 - Pi2
|
|
GOTO 5
|
|
8 A2M1 = A2M1 + Pi2
|
|
GOTO 5
|
|
|
|
9 Az = A1M2 / D2R
|
|
BAZ = A2M1 / D2R
|
|
|
|
!Fix the mirrored coords here.
|
|
|
|
az = 360.0 - az
|
|
baz = 360.0 - baz
|
|
|
|
999 return
|
|
end subroutine geodist
|