Azimuth Between two Points — get

Calculate initial bearing (or forward azimuth/direction) to go from point a to point b following great circle arc on a sphere.

Usage

get_azimuth(lat_a, lon_a, lat_b, lon_b)

Arguments

lat_a, lat_b: Numeric. Latitudes of a and b (in degrees).
lon_a, lon_b: Numeric. Longitudes of a and b (in degrees).

Value

numeric. Azimuth in degrees

Details

get_azimuth() is based on the spherical law of tangents. This formula is for the initial bearing (sometimes referred to as forward azimuth) which if followed in a straight line along a great circle arc will lead from the start point a to the end point b. $$\theta = \arctan2 (\sin \Delta\lambda \cos\psi_2, \cos\psi_1 \sin\psi_1-\sin\psi_1 \cos\psi_2 \cos\Delta\lambda)$$ where $\psi_1, \lambda_1$ is the start point, $\psi_2$, $\lambda_2$ the end point ($\Delta\lambda$ is the difference in longitude).

References

http://www.movable-type.co.uk/scripts/latlong.html

Examples

berlin <- c(52.517, 13.4) # Berlin
tokyo <- c(35.7, 139.767) # Tokyo
get_azimuth(berlin[1], berlin[2], tokyo[1], tokyo[2])
#> [1] 41.57361