deduplicate and correct ellipsoid specs, add third flattening

Author: scivision

pymap3d/ellipsoid.py

@@ -1,3 +1,4 @@
+from math import sqrt
 
 
 class Ellipsoid:
@@ -12,7 +13,6 @@ class Ellipsoid:
     """
 
     def __init__(self, model='wgs84'):
-        # type: (str) -> None
         """
         feel free to suggest additional ellipsoids
 
@@ -24,50 +24,44 @@ def __init__(self, model='wgs84'):
         if model == 'wgs84':
             """https://en.wikipedia.org/wiki/World_Geodetic_System#WGS84"""
             self.semimajor_axis = 6378137.
-            self.flattening = 1 / 298.2572235630
-            self.semiminor_axis = self.semimajor_axis * (1 - self.flattening)
+            self.semiminor_axis = 6356752.31424518
         elif model == 'wgs72':
             self.semimajor_axis = 6378135.
-            self.flattening = 1 / 298.26
-            self.semiminor_axis = self.semimajor_axis * (1 - self.flattening)
+            self.semiminor_axis = 6356750.52001609
         elif model == 'grs80':
             """https://en.wikipedia.org/wiki/GRS_80"""
             self.semimajor_axis = 6378137.
-            self.flattening = 1 / 298.257222100882711243
-            self.semiminor_axis = self.semimajor_axis * (1 - self.flattening)
+            self.semiminor_axis = 6356752.31414036
         elif model == 'clarke1866':
             self.semimajor_axis = 6378206.4
             self.semiminor_axis = 6356583.8
-            self.flattening = -(self.semiminor_axis / self.semimajor_axis - 1)
         elif model == 'mars':
             """
             https://tharsis.gsfc.nasa.gov/geodesy.html
             """
             self.semimajor_axis = 3396900.
             self.semiminor_axis = 3376097.80585952
-            self.flattening = 1 / 163.295274386012
         elif model == 'moon':
             self.semimajor_axis = 1738000.
             self.semiminor_axis = self.semimajor_axis
-            self.flattening = 0.
         elif model == 'venus':
             self.semimajor_axis = 6051000.
             self.semiminor_axis = self.semimajor_axis
-            self.flattening = 0.
         elif model == 'jupiter':
             self.semimajor_axis = 71492000.
-            self.flattening = 1 / 15.415446277169725
-            self.flattening = -(self.semiminor_axis / self.semimajor_axis - 1)
+            self.semiminor_axis = 66770054.3475922
         elif model == 'io':
             """
             https://doi.org/10.1006/icar.1998.5987
             """
             self.semimajor_axis = 1829.7
-            self.flattening = 1 / 131.633093525179
-            self.semiminor_axis = self.semimajor_axis * (1 - self.flattening)
+            self.semiminor_axis = 1815.8
         elif model == 'pluto':
             self.semimajor_axis = 1187000.
             self.semiminor_axis = self.semimajor_axis
-            self.flattening = 0.
         else:
             raise NotImplementedError('{} model not implemented, let us know and we will add it (or make a pull request)'.format(model))
+
+        self.flattening = (self.semimajor_axis - self.semiminor_axis) / self.semimajor_axis
+        self.thirdflattening = (self.semimajor_axis - self.semiminor_axis) / (self.semimajor_axis + self.semiminor_axis)
+        self.eccentricity = sqrt(2 * self.flattening - self.flattening**2)

tests/test_elliposid.py

@@ -6,6 +6,15 @@
 xyz0 = (660e3, -4700e3, 4247e3)
 
 
+@pytest.mark.parametrize("model,f", [("wgs84", 3.352810664747480e-03),
+                                     ("wgs72", 3.352779454167505e-03),
+                                     ("grs80", 3.352810681182319e-03),
+                                     ("clarke1866", 3.390075303928791e-03),
+                                     ("moon", 0.)])
+def test_reference(model, f):
+    assert pm.Ellipsoid(model).flattening == approx(f)
+
+
 def test_ellipsoid():
 
     assert pm.ecef2geodetic(*xyz0, ell=pm.Ellipsoid("wgs84")) == approx([42.014670535, -82.0064785, 276.9136916])