Better handle the near singularity case

Author: danineamati

notebooks/tutorials/utils/dop.ipynb

@@ -9,6 +9,7 @@
     "Dillution of Precision (DOP) describes the effect of satellite geometry on the \n",
     "user's positioning accuracy. \n",
     "DOP can refer to multiple ideas:\n",
+    "\n",
     "1. DOP in the horizontal or vertical direction,\n",
     "2. DOP on the time uncertainty,\n",
     "3. The full DOP matrix, or\n",
@@ -131,7 +132,7 @@
    "metadata": {},
    "outputs": [],
    "source": [
-    "dop_navdata = glp.get_dop(navdata, GDOP= True, HDOP=True, VDOP=True, \n",
+    "dop_navdata = glp.get_dop(navdata, GDOP= True, HDOP=True, VDOP=True,\n",
     "                          PDOP=True, TDOP=True, dop_matrix=True)\n",
     "print(dop_navdata)"
    ]

tests/utils/test_dop.py

@@ -391,21 +391,33 @@ def test_singularity_dop(navdata):
         A NavData with only one time entry of a *singular* satellite scenario.
 
     """
-    with pytest.raises(np.linalg.LinAlgError):
-        enut_matrix = _calculate_enut_matrix(navdata)
-        np.linalg.inv(enut_matrix.T @ enut_matrix)
 
-    # Now check that we get all NaNs for the DOP values when we have a
-    # singularity
+    # Run the DOP calculation
     dop_dict = calculate_dop(navdata)
 
     # Check the DOP output has all the expected keys
     assert dop_dict.keys() == {'dop_matrix',
-                               'GDOP', 'HDOP', 'VDOP', 'PDOP', 'TDOP'}
+                            'GDOP', 'HDOP', 'VDOP', 'PDOP', 'TDOP'}
+
+    try:
+        enut_matrix = _calculate_enut_matrix(navdata)
+        np.linalg.inv(enut_matrix.T @ enut_matrix)
 
-    # Check these are all NaNs
-    for _, val in dop_dict.items():
-        assert np.all(np.isnan(val))
+        # If we get here, then we did not get a singularity error
+        # This is possible due to floating point errors, so we will check
+        # that the values are unrealistically large.
+        # Note: we use np.any() since we can get small values in the DOP matrix
+        for _, val in dop_dict.items():
+            assert np.any(np.abs(val) > 1e6)
+
+    except np.linalg.LinAlgError:
+        # We expect a singularity error. If we get the singularity error, then
+        # the values should all be NaNs
+
+        # Now check that we get all NaNs for the DOP values when we have a
+        # singularity
+        for _, val in dop_dict.items():
+            assert np.all(np.isnan(val))
 
 
 #############################################