transverse_mercator.py

import math

# see conversion formulas at
# http://en.wikipedia.org/wiki/Transverse_Mercator_projection
# and
# http://mathworld.wolfram.com/MercatorProjection.html
class TransverseMercator:
    radius = 6378137

    def __init__(self, **kwargs):
        # setting default values
        self.lat = 0 # in degrees
        self.lon = 0 # in degrees
        self.k = 1 # scale factor
        
        for attr in kwargs:
            setattr(self, attr, kwargs[attr])
        self.latInRadians = math.radians(self.lat)

    def fromGeographic(self, lat, lon):
        lat = math.radians(lat)
        lon = math.radians(lon-self.lon)
        B = math.sin(lon) * math.cos(lat)
        x = 0.5 * self.k * self.radius * math.log((1+B)/(1-B))
        y = self.k * self.radius * ( math.atan(math.tan(lat)/math.cos(lon)) - self.latInRadians )
        return (x,y)

    def toGeographic(self, x, y):
        x = x/(self.k * self.radius)
        y = y/(self.k * self.radius)
        D = y + self.latInRadians
        lon = math.atan(math.sinh(x)/math.cos(D))
        lat = math.asin(math.sin(D)/math.cosh(x))

        lon = self.lon + math.degrees(lon)
        lat = math.degrees(lat)
        return (lat, lon)