Get lat/long given current point, distance and bearing

David M picture David M · Aug 28, 2011 · Viewed 96.1k times · Source

Given an existing point in lat/long, distance in (in KM) and bearing (in degrees converted to radians), I would like to calculate the new lat/long. This site crops up over and over again, but I just can't get the formula to work for me.

The formulas as taken the above link are:

lat2 = asin(sin(lat1)*cos(d/R) + cos(lat1)*sin(d/R)*cos(θ))

lon2 = lon1 + atan2(sin(θ)*sin(d/R)*cos(lat1), cos(d/R)−sin(lat1)*sin(lat2))

The above formula is for MSExcel where-

asin          = arc sin()   
d             = distance (in any unit)   
R             = Radius of the earth (in the same unit as above)  
and hence d/r = is the angular distance (in radians)  
atan2(a,b)    = arc tan(b/a)  
θ is the bearing (in radians, clockwise from north);  

Here's the code I've got in Python.

import math

R = 6378.1 #Radius of the Earth
brng = 1.57 #Bearing is 90 degrees converted to radians.
d = 15 #Distance in km

#lat2  52.20444 - the lat result I'm hoping for
#lon2  0.36056 - the long result I'm hoping for.

lat1 = 52.20472 * (math.pi * 180) #Current lat point converted to radians
lon1 = 0.14056 * (math.pi * 180) #Current long point converted to radians

lat2 = math.asin( math.sin(lat1)*math.cos(d/R) +
             math.cos(lat1)*math.sin(d/R)*math.cos(brng))

lon2 = lon1 + math.atan2(math.sin(brng)*math.sin(d/R)*math.cos(lat1),
                     math.cos(d/R)-math.sin(lat1)*math.sin(lat2))

print(lat2)
print(lon2)

I get

lat2 = 0.472492248844 
lon2 = 79.4821662373

Answer

David M picture David M · Oct 20, 2011

Needed to convert answers from radians back to degrees. Working code below:

import math

R = 6378.1 #Radius of the Earth
brng = 1.57 #Bearing is 90 degrees converted to radians.
d = 15 #Distance in km

#lat2  52.20444 - the lat result I'm hoping for
#lon2  0.36056 - the long result I'm hoping for.

lat1 = math.radians(52.20472) #Current lat point converted to radians
lon1 = math.radians(0.14056) #Current long point converted to radians

lat2 = math.asin( math.sin(lat1)*math.cos(d/R) +
     math.cos(lat1)*math.sin(d/R)*math.cos(brng))

lon2 = lon1 + math.atan2(math.sin(brng)*math.sin(d/R)*math.cos(lat1),
             math.cos(d/R)-math.sin(lat1)*math.sin(lat2))

lat2 = math.degrees(lat2)
lon2 = math.degrees(lon2)

print(lat2)
print(lon2)