question: public double greatCircleAzimuth ( Location location ) { if ( location == null ) { throw new IllegalArgumentException ( Logger . logMessage ( Logger . ERROR , "Location" , "greatCircleAzimuth" , "missingLocation" ) ) ; } double lat1 = Math . toRadians ( this . latitude ) ; double lon1 = Math . toRadians ( this . longitude ) ; double lat2 = Math . toRadians ( location . latitude ) ; double lon2 = Math . toRadians ( location . longitude ) ; if ( lat1 == lat2 && lon1 == lon2 ) { return 0 ; } if ( lon1 == lon2 ) { return lat1 > lat2 ? 180 : 0 ; } double y = Math . cos ( lat2 ) * Math . sin ( lon2 - lon1 ) ; double x = Math . cos ( lat1 ) * Math . sin ( lat2 ) - Math . sin ( lat1 ) * Math . cos ( lat2 ) * Math . cos ( lon2 - lon1 ) ; double azimuthRadians = Math . atan2 ( y , x ) ; return Double . isNaN ( azimuthRadians ) ? 0 : Math . toDegrees ( azimuthRadians ) ; }
target:  Computes the azimuth angle (clockwise from North) for the great circle path between this location and a specified location. This angle can be used as the starting azimuth for a great circle path beginning at this location, and passing through the specified location. This function uses a spherical model, not elliptical.