Considering Baxter's arms up to the wrist cuff, each arm has seven values that define the rotation angle of each joint. Since the link lengths and joint angles are known, it is possible to calculate the position and orientation of the gripper attached to the wrist. This approach to calculating the pose of the gripper given the configuration of the arm is called forward kinematic analysis.
Fortunately, ROS has programs that allow calculation and publishing of the joint angles given a particular position and orientation of the gripper. The particular topic for Baxter is
Baxter has seven joints in each of its two arms and two more joints in its head. The topic ...