Latency Meter: A device to measure end-to-end latency of VE systems

The effectiveness of virtual environment systems depends critically on the end-to-end delay between the user's motion and the update of the display. When the user moves, the graphics system must update the images on the display to reflect the proper projection of the virtual world on their field of vision. Significant delay in this update is perceived as swimming of the virtual world; objects in the virtual world appear to follow the user's motions. We are developing a standalone instrument that quickly estimates end-to-end latency without requiring electrical connections or changes to the VE software. We believe that a method for easily monitoring latency will change the way programmers and users work. Our latency meter works by observing the user's motion and the display's response using high-speed optical sensors. When the user rocks back and forth, the display exhibits a similar but delayed rocking of objects in the user's field of vision. We process the signals from the optical sensors to extract the times of very slow image change corresponding to the times when the user is nearly stopped (just before reversing direction). By correlating a sequence of these turn-around points in the two signals we can accurately estimate the end-to-end system delay.