  We present a robot kinematic calibration method that combines complementary
calibration approaches: self-contact, planar constraints, and self-observation.
We analyze the estimation of the end effector parameters, joint offsets of the
manipulators, calibration of the complete kinematic chain (DH parameters), and
we compare our results with ground truth measurements provided by a laser
tracker. Our main findings are: (1) When applying the complementary calibration
approaches in isolation, the self-contact approach yields the best and most
stable results. (2) All combinations of more than one approach were always
superior to using any single approach in terms of calibration errors as well as
the observability of the estimated parameters. Combining more approaches
delivers robot parameters that better generalize to the parts of workspace not
used for the calibration. (3) Sequential calibration, i.e.\ calibrating cameras
first and then robot kinematics, is more effective than simultaneous
calibration of all parameters. In real experiments, we employ two industrial
manipulators mounted on a common base. The manipulators are equipped with
force/torque sensors at their wrists, with two cameras attached to the robot
base, and with special end effectors with fiducial markers. We collect a new
comprehensive dataset for robot kinematic calibration and make it publicly
available. The dataset and its analysis provide quantitative and qualitative
insights that go beyond the specific manipulators used in this work and are
applicable to self-contained robot kinematic calibration in general.
