cedric's bazaar

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def EarthDistance((lat1, lon1), (lat2, lon2)):
    """
    Distance in meters between two points specified in degrees.
    """
    x1 = CalcRad(lat1) * math.cos(Deg2Rad(lon1)) * math.sin(Deg2Rad(90-lat1))
    x2 = CalcRad(lat2) * math.cos(Deg2Rad(lon2)) * math.sin(Deg2Rad(90-lat2))
    y1 = CalcRad(lat1) * math.sin(Deg2Rad(lon1)) * math.sin(Deg2Rad(90-lat1))
    y2 = CalcRad(lat2) * math.sin(Deg2Rad(lon2)) * math.sin(Deg2Rad(90-lat2))
    z1 = CalcRad(lat1) * math.cos(Deg2Rad(90-lat1))
    z2 = CalcRad(lat2) * math.cos(Deg2Rad(90-lat2))
    a = (x1*x2 + y1*y2 + z1*z2)/pow(CalcRad((lat1+lat2)/2), 2)
    # a should be in [1, -1] but can sometimes fall outside it by
    # a very small amount due to rounding errors in the preceding
    # calculations (this is prone to happen when the argument points
    # are very close together).  Thus we constrain it here.
    if abs(a) > 1:
        a = 1
    elif a < -1:
        a = -1
    return CalcRad((lat1+lat2) / 2) * math.acos(a)

def MeterOffset((lat1, lon1), (lat2, lon2)):
    """
    Return offset in meters of second arg from first.
    """
    dx = EarthDistance((lat1, lon1), (lat1, lon2))
    dy = EarthDistance((lat1, lon1), (lat2, lon1))
    if lat1 < lat2:
        dy *= -1
    if lon1 < lon2:
        dx *= -1
    return (dx, dy)