pythonishvili - 5 months ago 22

Python Question

I tried implementing this formula: http://andrew.hedges.name/experiments/haversine/

The aplet does good for the two points I am testing:

Yet my code is not working.

`from math import sin, cos, sqrt, atan2`

R = 6373.0

lat1 = 52.2296756

lon1 = 21.0122287

lat2 = 52.406374

lon2 = 16.9251681

dlon = lon2 - lon1

dlat = lat2 - lat1

a = (sin(dlat/2))**2 + cos(lat1) * cos(lat2) * (sin(dlon/2))**2

c = 2 * atan2(sqrt(a), sqrt(1-a))

distance = R * c

print "Result", distance

print "Should be", 278.546

The distance it returns is

Answer

It's because in Python, all the trig functions use radians, not degrees.

You can either convert the numbers manually to radians, or use the `radians`

function from the math module:

```
from math import sin, cos, sqrt, atan2, radians
# approximate radius of earth in km
R = 6373.0
lat1 = radians(52.2296756)
lon1 = radians(21.0122287)
lat2 = radians(52.406374)
lon2 = radians(16.9251681)
dlon = lon2 - lon1
dlat = lat2 - lat1
a = sin(dlat / 2)**2 + cos(lat1) * cos(lat2) * sin(dlon / 2)**2
c = 2 * atan2(sqrt(a), sqrt(1 - a))
distance = R * c
print("Result:", distance)
print("Should be:", 278.546, "km")
```

The distance is now returning the correct value of `278.545589351`

km.