model: read inertia stored within the frame

src/multibody/model.hpp

@@ -525,6 +525,7 @@ namespace pinocchio
     
     ///
     /// \brief Adds a frame to the kinematic tree.
+    ///        The inertia stored within the frame will be happened to the inertia supported by the joint (frame.parent).
     ///
     /// \param[in] frame The frame to add to the kinematic tree.
     ///

src/multibody/model.hxx

@@ -278,13 +278,16 @@ namespace pinocchio
   ModelTpl<Scalar,Options,JointCollectionTpl>::
   addFrame(const Frame & frame)
   {
+    PINOCCHIO_CHECK_INPUT_ARGUMENT(frame.parent >= 0 && frame.parent < njoints,
+                                   "The index of the parent frame is not valid.");
+    
     // Check if the frame.name exists with the same type
     if(existFrame(frame.name,frame.type))
-    {
       return getFrameId(frame.name,frame.type);
-    }
+    
     // else: we must add a new frames to the current stack
     frames.push_back(frame);
+    inertias[frame.parent] += frame.placement.act(frame.inertia);
     nframes++;
     return FrameIndex(nframes - 1);
   }