refactor: Enhance OneEuroFilter with type hints and error handling improvements

- Added overloads for the `_smoothing_factor` method to improve type hinting for different input types.
- Enhanced error handling in the timestamp validation to provide clearer feedback when an invalid timestamp is encountered.
- Streamlined the calculation of the filtered velocity by simplifying the logic in the `update` method.
- Improved code organization with additional type annotations for better clarity and maintainability.

app/tracking/__init__.py

@@ -317,6 +317,15 @@ class OneEuroFilter(GenericVelocityFilter):
         self._x_filtered = keypoints  # Position filter state
         self._dx_filtered = None  # Initially no velocity estimate
 
+    @overload
+    def _smoothing_factor(self, cutoff: float, dt: float) -> float: ...
+
+    @overload
+    def _smoothing_factor(
+        self, cutoff: Float[Array, "J"], dt: float
+    ) -> Float[Array, "J"]: ...
+
+    @jaxtyped(typechecker=beartype)
     def _smoothing_factor(
         self, cutoff: Union[float, Float[Array, "J"]], dt: float
     ) -> Union[float, Float[Array, "J"]]:
@@ -324,6 +333,7 @@ class OneEuroFilter(GenericVelocityFilter):
         r = 2 * jnp.pi * cutoff * dt
         return r / (r + 1)
 
+    @jaxtyped(typechecker=beartype)
     def _exponential_smoothing(
         self,
         a: Union[float, Float[Array, "J"]],
@@ -367,13 +377,12 @@ class OneEuroFilter(GenericVelocityFilter):
         """
         dt = (timestamp - self._last_timestamp).total_seconds()
         if dt <= 0:
-            raise ValueError("invalid timestamp")
-
-        # Compute velocity from current input and filtered state
-        dx = (
-            (keypoints - self._x_filtered) / dt if dt > 0 else jnp.zeros_like(keypoints)
+            raise ValueError(
+                f"new timestamp is not greater than the last timestamp; expecting: {timestamp} > {self._last_timestamp}"
             )
 
+        dx = (keypoints - self._x_filtered) / dt
+
         # Determine cutoff frequency based on movement speed
         cutoff = self._min_cutoff + self._beta * jnp.linalg.norm(
             dx, axis=-1, keepdims=True
@@ -392,9 +401,7 @@ class OneEuroFilter(GenericVelocityFilter):
         )
 
         # Apply low-pass filter to position with adaptive cutoff
-        a_cutoff = self._smoothing_factor(
-            jnp.asarray(cutoff), dt
-        )  # Convert cutoff to scalar if needed
+        a_cutoff = self._smoothing_factor(jnp.asarray(cutoff), dt)
         self._x_filtered = self._exponential_smoothing(
             a_cutoff, keypoints, self._x_filtered
         )