get_shadow_length.py

import ephem
import numpy as np
from datetime import datetime

def get_shadow_length(long, lat, datetime, height):
    """
    Accepts longitude and latitude in the WGS84 CRS, along with the
    datetime in the UTC time zone. Returns the length of a shadow of an object
    with a specified height at the specified time and location.
    """
    o = ephem.Observer()
    o.long, o.lat = str(long), str(lat)
    o.date = ephem.Date(datetime)
    sun = ephem.Sun(o)
    az = sun.az * 180/np.pi
    zen = 90 - sun.alt*180/np.pi
    shadow = 1 / np.tan(sun.alt)
    return shadow