Work around warning when dividing by zero

stpt_pipeline/stpt_displacement.py

@@ -88,16 +88,18 @@ def get_coords(coords, cof, center_x, max_x, direct=True):
     max_desp = cof[0] * coords[1] ** 2 + cof[1] * coords[1] + cof[2]
     dy_cof = max_desp / (max_x - center_x) ** 2
     if direct:
-        sign = (coords[0] - center_x) / np.abs(coords[0] - center_x)
-        if np.isnan(sign):
-            sign = 1.0
+        if coords[0] > center_x:
+            sign = 1
+        else:
+            sign = -1
         xi = np.abs(coords[0] - center_x)
         return (center_x + sign * (xi + dy_cof * xi ** 2), coords[1])
     else:
+        if coords[0] > center_x + cof[2]:
+            sign = 1
+        else:
+            sign = -1
         xi = np.abs(coords[0] - center_x - cof[2])
-        sign = (coords[0] - center_x - cof[2]) / np.abs(coords[0] - center_x - cof[2])
-        if np.isnan(sign):
-            sign = 1.0
         return (
             center_x + sign * (np.sqrt(1 + 4 * dy_cof * xi) - 1) / (2 * dy_cof),
             coords[1],