research: Dütsch driver — exact-point body mask, periodic geometry from step mod T

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

research/duetsch_re100_kc5/protocol.py

@@ -25,12 +25,15 @@ def amplitude(D):
 
 
 def position(s, T, A):
-    """Centre position relative to the mean: x = A cos(2 pi s / T)."""
-    return A * math.cos(2.0 * math.pi * s / T)
+    """Centre position relative to the mean: x = A cos(2 pi s / T), evaluated from the
+    native step modulo T so every cycle repeats the same geometry bit for bit."""
+    return A * math.cos(2.0 * math.pi * (int(s) % T) / T)
 
 
 def phase(s, T):
-    return (360.0 * s / T - 90.0) % 360.0
+    """Paper phase in degrees from the native step modulo T (the unwrapped cycle
+    index is kept separately by ``cycle``)."""
+    return (360.0 * (int(s) % T) / T - 90.0) % 360.0
 
 
 def cycle(s, T):
@@ -63,6 +66,18 @@ def morison_fit(f_norm, b1, b2):
     return float(c_d), float(c_i)
 
 
+def inside_circle(x, y, centre, radius):
+    return (x - centre[0]) ** 2 + (y - centre[1]) ** 2 < radius * radius
+
+
+def sample(field, fluid, x, y, centre, radius):
+    """Profile sample: MISSING if the exact point is inside the body (checked before
+    any corner interpolation), else ``bilinear_fluid``."""
+    if inside_circle(x, y, centre, radius):
+        return None, (), 0.0
+    return bilinear_fluid(field, fluid, x, y)
+
+
 def bilinear_fluid(field, fluid, x, y):
     """Bilinear value at (x, y) in cell coordinates from fluid cells only.