Learning Geospatial Analysis with Python - Second Edition

Calculating line direction

In addition to distance, you'll often want to know the bearing of a line between its end points. We can calculate this line direction from one of the points using only the Python math module, as shown in the following calculation:

>>> from math import atan2, cos, sin, degrees
>>> lon1 = -90.21
>>> lat1 = 32.31
>>> lon2 = -88.95
>>> lat2 = 30.43
>>> angle = atan2(cos(lat1)*sin(lat2)-sin(lat1) *
>>>     cos(lat2)*cos(lon2-lon1), sin(lon2-lon1)*cos(lat2))
>>> bearing = (degrees(angle) + 360) % 360
>>> print(bearing)
309.3672990606595

Sometimes, you end up with a negative bearing value. To avoid this issue, we add 360 to the result to avoid a negative number and use the Python module operator to keep the value from climbing over ...