give warning for undefined behavior

CHANGELOG.md

@@ -9,9 +9,14 @@
 
 - Properties on `CameraModel` (e.g. `cam.M`) are deprecated and will
   be removed in a future release.
+
 - Intrinsic parameter matrix is normalized upon loading in
   `CameraModel._from_parts`, which is called by most constructors.
 
+- If an input calibration has a non-normalized P matrix and a
+  rectification matrix, a warning is given as this case is not well
+  tested and the behavior should be considered undefined.
+
 ## Bugfixes
 
 - Mirroring and flipping cameras with skew, distortion, and

pymvg/camera_model.py

@@ -203,7 +203,14 @@ def _from_parts(cls,
                 if np.allclose(rect,np.eye(3)):
                     rect = None
 
-        P = P/P[2,2] # normalize
+        denom = P[2,2]
+        if denom != 1.0:
+            if rect is not None:
+                warnings.warn(
+                    'A non-normalized P matrix and a rectification matrix were '
+                    'supplied. This case is not well tested and the behavior '
+                    'should be considered undefined.')
+            P = P/denom # normalize
         result = cls(name, width, height, _rquat, camcenter, P, K, distortion, rect)
         return result