feat: add basic trajectory metrics

movement/kinematics/__init__.py

@@ -33,3 +33,4 @@
     "compute_forward_vector_angle",
     "compute_kinetic_energy",
 ]
+from .trajectory_metrics import trajectory_length, trajectory_variance

movement/kinematics/trajectory_metrics.py

@@ -0,0 +1,9 @@
+import numpy as np
+
+
+def trajectory_length(traj):
+    return np.sum(np.linalg.norm(np.diff(traj, axis=0), axis=1))
+
+
+def trajectory_variance(traj):
+    return np.var(traj, axis=0).sum()

tests/test_trajectory_metrics.py

@@ -0,0 +1,8 @@
+import numpy as np
+
+from movement.kinematics.trajectory_metrics import trajectory_length
+
+
+def test_trajectory_length():
+    traj = np.array([[0, 0], [3, 4]])
+    assert trajectory_length(traj) == 5.0