src/aarecommon/math/find_xtal.py

@@ -323,9 +323,31 @@ def raster_centre_of_mass(result_array, images) -> CenterOfMassModel | None:
     return _to_com_model(com, images, "Center of mass")
 
 
-def raster_highest_score(images) -> CenterOfMassModel | None:
-    """Target the grid cell with the highest crystal score (compute_crystal_score_array)."""
+def raster_highest_score(
+    images,
+    min_low_res_spots: float = 10.0,
+    min_spots_indexed: int = 1,
+) -> CenterOfMassModel | None:
+    """Target the grid cell with the highest crystal score.
+
+    If the whole grid is too weak to hold a crystal — max spots_low_res below
+    min_low_res_spots OR max spots_indexed below min_spots_indexed — target the
+    geometric centre of the grid instead of collecting at a noisy cell, so a
+    'nothing here' result is centred and deliberate rather than random noise.
+    """
     score_array = compute_crystal_score_array(images)
+    max_low_res = max((getattr(img, "spots_low_res", 0) or 0 for img in images), default=0)
+    max_indexed = max((getattr(img, "spots_indexed", 0) or 0 for img in images), default=0)
+    if max_low_res < min_low_res_spots or max_indexed < min_spots_indexed:
+        n_nx, n_ny = score_array.shape
+        logger.info(
+            f"No crystal in loop (max spots_low_res={max_low_res} < {min_low_res_spots} "
+            f"or max spots_indexed={max_indexed} < {min_spots_indexed}); "
+            f"targeting grid centre of {n_nx}x{n_ny} grid"
+        )
+        # get_com_mm maps index i -> (i+0.5)*step, so index (N-1)/2 is the true
+        # geometric centre of the grid for both odd and even N (and N==1).
+        return CenterOfMassModel(n_x=(n_nx - 1) / 2.0, n_y=(n_ny - 1) / 2.0)
     return _to_com_model(_max_cell(score_array), images, "Highest score")
 
 
@@ -650,3 +672,29 @@ def compare_crystal_methods_scored(
     )
     plt.tight_layout()
     plt.show()
+
+
+if __name__ == "__main__":
+    from types import SimpleNamespace as _I
+
+    def _cell(nx, ny, low, idx, bkg=0):
+        return _I(nx=nx, ny=ny, number=nx * 3 + ny,
+                  spots_low_res=low, spots_indexed=idx, bkg=bkg)
+
+    # Real crystal at (1,1) -> best cell returned.
+    strong = [_cell(x, y, 0, 0) for x in range(3) for y in range(3)]
+    strong[4] = _cell(1, 1, 50, 5, bkg=100)
+    com = raster_highest_score(strong)
+    assert (round(com.n_x), round(com.n_y)) == (1, 1), com
+
+    # All noise (low-res < 10, nothing indexed) -> centre of 3x3 grid == (1,1).
+    noise = [_cell(x, y, 3, 0) for x in range(3) for y in range(3)]
+    com = raster_highest_score(noise)
+    assert (com.n_x, com.n_y) == (1.0, 1.0), com
+
+    # Strong low-res but nothing indexed anywhere -> OR rule routes to centre.
+    no_index = [_cell(x, y, 40, 0) for x in range(3) for y in range(3)]
+    com = raster_highest_score(no_index)
+    assert (com.n_x, com.n_y) == (1.0, 1.0), com
+
+    print("find_xtal self-check passed")