update examples to fix path issues

examples/viz/signal_filters.py

@@ -1,5 +1,32 @@
 """Signal filtering helpers for example force charts."""
 
-from orisys.signal_processing import lowpass_filter
+from __future__ import annotations
 
-__all__ = ["lowpass_filter"]
+import numpy as np
+from scipy.signal import butter, filtfilt
+
+def lowpass_filter(data, cutoff_hz=5, sample_rate_hz=30, order=2) -> np.ndarray:
+    """Zero-phase Butterworth low-pass filter for uniformly sampled 1-D data."""
+    y = np.asarray(data, dtype=np.float64)
+    if cutoff_hz == 0:
+        return y.copy()
+    if y.size == 0:
+        return y
+
+    nyquist = 0.5 * sample_rate_hz
+    if cutoff_hz < 0 or cutoff_hz >= nyquist:
+        raise ValueError(
+            f"cutoff_hz must be in (0, {nyquist}) for sample_rate_hz={sample_rate_hz}"
+        )
+
+    b, a = butter(order, cutoff_hz / nyquist, btype="low")
+    taplen = max(len(a), len(b))
+    # scipy.signal.filtfilt requires len(x) > padlen (default 3 * taplen for recent scipy).
+    padlen = 3 * taplen
+    if y.size <= padlen:
+        return y.copy()
+
+    try:
+        return filtfilt(b, a, y)
+    except ValueError:
+        return y.copy()