Address review comments

gwcs/region.py

@@ -14,6 +14,7 @@
 
 __all__ = ['Region', 'Edge', 'Polygon']
 
+_INTERSECT_ATOL = 1e2 * np.finfo(float).eps
 
 class Region:
     """
@@ -390,24 +391,30 @@ def intersection(self, edge):
         v = edge._stop - edge._start
         w = self._start - edge._start
 
-        # Find the determinant of the matrix formed by the vectors u and v
-        #    Note: Originally this was computed using a numpy "2D" cross product,
-        #          however, this functionality has been deprecated and slated for
-        #          removal.
-        D = np.linalg.det([u, v])
+        D = _det(u, v)
 
-        if np.allclose(D, 0, rtol=0, atol=1e2 * np.finfo(float).eps):
+        if abs(D) < _INTERSECT_ATOL:
             return np.array(self._start)
 
-        # See note above
-        return np.linalg.det([v, w]) / D * u + self._start
+        return _det(v, w) / D * u + self._start
 
     def is_parallel(self, edge):
         u = self._stop - self._start
         v = edge._stop - edge._start
-        return np.allclose(
-            np.linalg.det([u, v]), 0, rtol=0, atol=1e2 * np.finfo(float).eps
-        )
+        return np.allclose(_det(u, v), 0, rtol=0, atol=_INTERSECT_ATOL)
+
+
+def _det(u, v):
+    """
+    Find the determinant of the matrix formed by the vectors u and v
+
+    Note: Originally this was computed using a numpy "2D" cross product,
+          however, this functionality has been deprecated and slated for
+          removal.
+    Note: This is marginally faster than using `np.linalg.det([u, v])` by ~10ms
+          during empirical testing
+    """
+    return u[0] * v[1] - u[1] * v[0]
 
 
 def _round_vertex(v):