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cs_lang:python:things-to-know:geographic
```def Deg2Rad(x):
"""
"""
return x * (math.pi/180)

"""
"""
return x * (180/math.pi)

"""
Radius of curvature in meters at specified latitude.
"""
a = 6378.137
e2 = 0.081082 * 0.081082
# the radius of curvature of an ellipsoidal Earth in the plane of a
# meridian of latitude is given by
#
# R' = a * (1 - e^2) / (1 - e^2 * (sin(lat))^2)^(3/2)
#
# where a is the equatorial radius,
# b is the polar radius, and
# e is the eccentricity of the ellipsoid = sqrt(1 - b^2/a^2)
#
# a = 6378 km (3963 mi) Equatorial radius (surface to center distance)
# b = 6356.752 km (3950 mi) Polar radius (surface to center distance)
# e = 0.081082 Eccentricity
x = a * (1.0 - e2)
z = 1.0 - e2 * sc * sc
y = pow(z, 1.5)
r = x / y

r = r * 1000.0      # Convert to meters
return r

def EarthDistance((lat1, lon1), (lat2, lon2)):
"""
Distance in meters between two points specified in degrees.
"""
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)``` 