Eventley/longlat.py at master · codeb1ooded/Eventley · GitHub

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import math
def deg2rad(degrees):
    return 3.14*degrees/180.0
# radians to degrees
def rad2deg(radians):
    return 180.0*radians/3.14

# Semi-axes of WGS-84 geoidal reference
WGS84_a = 6378137.0  # Major semiaxis [m]
WGS84_b = 6356752.3  # Minor semiaxis [m]

# Earth radius at a given latitude, according to the WGS-84 ellipsoid [m]
def WGS84EarthRadius(lat):
    # http://en.wikipedia.org/wiki/Earth_radius
    An = WGS84_a*WGS84_a * math.cos(lat)
    Bn = WGS84_b*WGS84_b * math.sin(lat)
    Ad = WGS84_a * math.cos(lat)
    Bd = WGS84_b * math.sin(lat)
    return math.sqrt( (An*An + Bn*Bn)/(Ad*Ad + Bd*Bd) )

# Bounding box surrounding the point at given coordinates,
# assuming local approximation of Earth surface as a sphere
# of radius given by WGS84
def boundingBox(latitudeInDegrees, longitudeInDegrees, halfSideInKm):
    lat = deg2rad(latitudeInDegrees)
    lon = deg2rad(longitudeInDegrees)
    halfSide = 1000*halfSideInKm

    # Radius of Earth at given latitude
    radius = WGS84EarthRadius(lat)
    # Radius of the parallel at given latitude
    pradius = radius*math.cos(lat)

    latMin = lat - halfSide/radius
    latMax = lat + halfSide/radius
    lonMin = lon - halfSide/pradius
    lonMax = lon + halfSide/pradius

    print str(rad2deg(latMin))
    print str(rad2deg(lonMin))
    print str(rad2deg(latMax))
    print str(rad2deg(lonMax))
boundingBox(77,28,5)