April 3, 2018

By: Wayne Dyck
## Calculate distance between latitude longitude pairs with Python

The Haversine formula is an equation that can be used to find great-circle distances between two points on a sphere from their longitudes and latitudes. When this formula is applied to the earth the results are an approximation because the Earth is not a perfect sphere. The currently accepted (WGS84) radius at the equator is 6378.137 km and 6356.752 km at the polar caps. For aviation purposes we typically use a radius of 6371.0 km.

```
#!/usr/bin/env python
# Haversine formula example in Python
# Author: Wayne Dyck
import math
def distance(origin, destination):
lat1, lon1 = origin
lat2, lon2 = destination
radius = 6371 # km
dlat = math.radians(lat2-lat1)
dlon = math.radians(lon2-lon1)
a = math.sin(dlat/2) * math.sin(dlat/2) + math.cos(math.radians(lat1)) \
* math.cos(math.radians(lat2)) * math.sin(dlon/2) * math.sin(dlon/2)
c = 2 * math.atan2(math.sqrt(a), math.sqrt(1-a))
d = radius * c
return d
```

Saving the above script as `haversine.py`

you can also use it interactively within the Python shell like this,

```
>>> import haversine
>>> seattle = [47.621800, -122.350326]
>>> olympia = [47.041917, -122.893766]
>>> haversine.distance(seattle, olympia)
76.386615799548693
>>>
```