draft

position.py

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+#!/usr/bin/env python3
+
+import math
+
+def arc_to_deg(arc):
+    """convert spherical arc length [m] to great circle distance [deg]"""
+    return float(arc)/6371/1000 * 180/math.pi
+
+def deg_to_arc(deg):
+    """convert great circle distance [deg] to spherical arc length [m]"""
+    return float(deg)*6371*1000 * math.pi/180
+
+def latlon_to_xyz(lat,lon):
+    """Convert angluar to cartesian coordiantes
+
+    latitude is the 90deg - zenith angle in range [-90;90]
+    lonitude is the azimuthal angle in range [-180;180] 
+    """
+    r = 6371 # https://en.wikipedia.org/wiki/Earth_radius
+    theta = math.pi/2 - math.radians(lat) 
+    phi = math.radians(lon)
+    x = r * math.sin(theta) * math.cos(phi) # bronstein (3.381a)
+    y = r * math.sin(theta) * math.sin(phi)
+    z = r * math.cos(theta)
+    return [x,y,z]
+
+def xyz_to_latlon (x,y,z):
+    """Convert cartesian to angular lat/lon coordiantes"""
+    r = math.sqrt(x**2 + y**2 + z**2)
+    theta = math.asin(z/r) # https://stackoverflow.com/a/1185413/4933053
+    phi = math.atan2(y,x)
+    lat = math.degrees(theta)
+    lon = math.degrees(phi)
+    return [lat,lon]