VRSG Multi-Channel Synchronization

MetaVR VRSG establishes and maintains scene synchronization across multiple networked channels by means of a CAT5 or CAT6 Ethernet cable.

VRSG controls the scene content across all channels to:

• Ensure that the image processing and storage capacity of the PC IG is efficiently used, but not exceeded, for all conditions.
• Ensure continuity of the scene and prevent "popping" of scene elements.
• Prevent and correct overload conditions.
• Ensure point lights are properly faded to prevent "popping".
• Eliminate scene details too small to contribute to visual cueing.
• Ensure scene detail is maintained within the FOV according to priority needs for the viewer.

One of the cockpit simulators at the new F-16 Mission Training Center, located at the ANG base at the Burlington International Airport, Burlington, VT. The multi-channel synchronized view, driven by MetaVR VRSG, is rendering the VT virtual terrain built by MetaVR. Photo courtesy of SSgt. Dan DiPietro of the Vermont Air National Guard.

Scene load management

VRSG implements scene management through level-of-detail (LOD) scaling. Moving models and terrain database features might require use of LOD switches, which indicate the needed switch-in and switch-out ranges for various levels of complexity. VRSG uses a control loop on an LOD scale, which modulates LOD ranges based on loading conditions. For example, under conditions of high load, LOD ranges might be scaled to smaller values so that a less complex version of a model might be selected sooner than it normally would. This scaling maintains a target frame rate, while maximizing image density. After the heavy load condition passes, the level of detail ranges return to their default values. This technique guarantees that viewers see every object in the scene regardless of load conditions. Showing viewers a lower complexity version of a model is preferred to completely eliminating the model from the scene under high load conditions.

Continuous image density

VRSG continuously monitors its load conditions to maximize image density. During each frame, the control loop on the LOD scale is adjusted upward if loading conditions warrant the ability to provide more detail, or downward if loading conditions threaten to violate the 30-60 Hz update rate. Each visual channel manages its scene density independently of the others.

Synchronization

VRSG provides a 30-60 Hz sync signal that is continuous at all times and has a maximum tolerance of +/- 0.1 Hz. This sync signal is provided by the host-side API.

Although VRSG controls the scene content to be rendered on all channels and displays, its synchronization does not output the video reference signal ensuring the synchronization of signals on multiple display devices. This means that if one channel slows down, for example to a frame rate of 30 Hz, all the channels slow down. If you need to align the timing of the channels' vertical retraces, consider using ATI CrossFire or NVIDIA SLI genlock graphic cards or multi-media production genlock boards.