Casting BasePtr to Simbody joint; header file missing

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I have a BasePtr of Type Id 9, which accroding to the docs is a ball joint. I want to cast this pointer via:

gazebo::physics::BallJoint<SimbodyJoint> joint = boost::dynamic_pointer_cast<gazebo::physics::BallJoint<SimbodyJoint>>(base);

But I get the following error message when trying to compile:

/usr/include/gazebo-7/gazebo/physics/simbody/simbody_inc.h:22:21: fatal error: Simbody.h: No such file or directory

I installed installed simbody from the repo but I get the same error message.

What can I do?