Add NSD Calculation (#302)

ecoscope/base/base.py

@@ -412,6 +412,7 @@ def _create_trajsegments(gdf):
                 "heading": track_properties.heading,
                 "geometry": shapely.linestrings(coords),
                 "junk_status": gdf.junk_status,
+                "nsd": track_properties.nsd,
             },
             crs=4326,
             index=gdf.index,
@@ -625,6 +626,13 @@ def dist_meters(self):
                 _, _, distance = self.inverse_transformation
                 return distance
 
+            @property
+            def nsd(self):
+                start_point = df["geometry"].iloc[0]
+                geod = Geod(ellps="WGS84")
+                geod_displacement = [geod.inv(start_point.x, start_point.y, geo.x, geo.y)[2] for geo in df["_geometry"]]
+                return [(x**2) / (1000 * 2) for x in geod_displacement]
+
             @property
             def timespan_seconds(self):
                 return (df["_fixtime"] - df["fixtime"]).dt.total_seconds()

tests/test_base.py

@@ -50,6 +50,30 @@ def test_relocations_from_gdf_preserve_fields(er_io):
     gpd.testing.assert_geodataframe_equal(relocations, ecoscope.base.Relocations.from_gdf(relocations))
 
 
+def test_trajectory_properties(movebank_relocations):
+    trajectory = ecoscope.base.Trajectory.from_relocations(movebank_relocations)
+
+    assert "groupby_col" in trajectory
+    assert "segment_start" in trajectory
+    assert "segment_end" in trajectory
+    assert "timespan_seconds" in trajectory
+    assert "speed_kmhr" in trajectory
+    assert "heading" in trajectory
+    assert "geometry" in trajectory
+    assert "junk_status" in trajectory
+    assert "nsd" in trajectory
+
+    trajectory = trajectory.loc[trajectory.groupby_col == "Habiba"].head(5)
+
+    expected_nsd = pd.Series(
+        [0.446425, 1.803153, 2.916319, 28.909629, 72.475410],
+        dtype=np.float64,
+        index=pd.Index([368706890, 368706891, 368706892, 368706893, 368706894], name="event-id"),
+        name="nsd",
+    )
+    pandas.testing.assert_series_equal(trajectory["nsd"], expected_nsd)
+
+
 def test_displacement_property(movebank_relocations):
     trajectory = ecoscope.base.Trajectory.from_relocations(movebank_relocations)
     expected = pd.Series(