MapBasic Code. Copy/Paste if needed.

include "GC_Constants.def" include "GC_Azimuth.def" '====================================================================== function GreatCircleAzimuth (    byval fLon0 as float,    'Origin longitude    byval fLat0 as float,    'Origin latitude    byval fLon1 as float,    'Destination longitude    byval fLat1 as float)    'Destination latitude    as float                 'Azimuth bearing 'Calculates the azimuth that the destination point bears to the 'origin. Azimuth is returned as decimal degrees. '---------------------------------------------------------------------- dim a, b as float dim fAdjust as float dim lat0, lon0, lat1, lon1 as float    lat0 = fLat0 * DEG2RAD    lon0 = fLon0 * DEG2RAD    lat1 = fLat1 * DEG2RAD    lon1 = fLon1 * DEG2RAD     a = cos(lat1) * sin(lon1 - lon0)    b = cos(lat0) * sin(lat1) - sin(lat0) * cos(lat1) * cos(lon1 - lon0)    'perform quadrant adjustment    if a = 0 and b = 0 then       GreatCircleAzimuth = 0       exit function    end if    if b = 0 then       if a < 0 then          GreatCircleAzimuth = 270       else          GreatCircleAzimuth = 90       end if       exit function    end if    if b < 0 then       fAdjust = PI    else       if a < 0 then          fAdjust = 2 * PI       else          fAdjust = 0       end if    end if    GreatCircleAzimuth = (atn(a/b) + fAdjust) * RAD2DEG end function