In this experiment, a person's head was tracked using both the vision algorithm and the Polhemus magnetic sensor 6 simultaneously. Figure 9 shows the vision estimate and Polhemus measurements (after an absolute orientation  was performed to align the estimates properly). The RMS difference in translation is 0.11 units and the RMS difference in rotation is . (The scale of translation is, of course, unknown, but is approximately 10-12cm per unit, yielding a RMS tracking error of approximately 1 cm.) This yields accuracy on the order of the observed accuracy of the Polhemus sensor, indicating that the vision estimate is at least as accurate as the Polhemus sensor.
This example is identical to the example presented in our earlier work on vision-based head tracking , except here we recover focal length and structure simultaneously with motion. The previous work relied on a rough, a priori structural model and calibration of focal length. The RMS errors between vision and Polhemus estimates for this example were slightly better than those in the previous study, (1cm versus 1.67cm and 2.35 degrees versus 2.4 degrees).