Outline General Principles of Distributed Virtual Environments: - PDF document

Outline General Principles of Distributed Virtual Environments: CSCI 8220 Parallel & Distributed ! What are they? Simulation ! Distributed Virtual Environments (DVE) versus Analytical Simulations Distributed Virtual Environments ! Distributed Interactive Simulation (DIS) Introduction DVE Techniques: ! Dead Reckoning 2 Maria Hybinette, UGA Maria Hybinette, UGA Distributed Virtual Environments (DVE) DVE: Goals ! A synthetic world into which humans and/or ! Sufficiently Realistic Representation physical devices are embedded » ‘ Realistic ’ application dependent (e.g., training) » Interaction between embedded and simulated ! Consistent views elements » Each participant have consistent views of the DVE ! Geographically distributed: Involves humans, devices and computations at different » Consistent in time and space locations ! Fair fight: ! Examples » Outcome depends on the skill of the player rather » Military training (SIMNET, Distributed Interactive than on artifacts in the environment Simulation, HLA) ! Latency & limited communication bandwidth » Multiplayer video games 3 4 Maria Hybinette, UGA Maria Hybinette, UGA Review: Analytic vs. DVE DVE Architectures (Training) WAN interconnect � Analytical DVE LAN interconnect � Simulation Model May be non-interactive Interactive As-fast-as-possible Real-time Performance Speedup Realism Often point to point Broad/Multicast Reliable Best effort Communication Multiprocessor/LAN LAN/WAN OK w/arbitrary latencies Latency bounds,low jitter Time stamp order Receive Order Time Management Synchronization Protocols No Synchronization Protocols Efficient execution Issues Training, Scalable execution Easy of use Server Architecture � Distributed Architecture � Typical Appications Design Analysis Training, entertainment 5 6 Maria Hybinette, UGA Maria Hybinette, UGA

Distributed Interactive Simulation (DIS) DIS Design Principles “ The primary mission of DIS is to define an infrastructure for linking simulations of various types at multiple locations to create realistic, complex, virtual ‘ worlds ’ for the simulation of highly interactive activities ” [DIS Vision, 1994]. ! Autonomy of simulation nodes » simulations broadcast events of interest to other simulations; need not determine which others need information » receivers determine if information is relevant to it, and model local effects of new information » simulations may join or leave exercises in progress ! Transmission of “ ground truth ” information » each simulation transmits absolute truth about state of its objects ! Developed in U.S. Department of Defense, initially for training » receiver is responsible for appropriately “ degrading ” information (e.g., due to environment, sensor ! DVEs widely used in DoD; growing use in other areas characteristics) (entertainment, emergency planning, air traffic control) 8 Maria Hybinette, UGA A Typical DVE Node Simulator DIS Design Principles network Execute every 1/30th of a second: � visual display system ! Transmission of state change information only Image network » if behav i or “ stays the same ” (e.g., straight and level flight), state Generator interface Other Vehicle updates drop to a predetermined rate (e.g., every five seconds) State Table terrain ! “ Dead Reckoning ” algorithms database control/ own vehicle sound display » extrapolate current position of moving objects based on last dynamics generator interface reported position ! Simulation time constraints controls and panels » many simulations are human-in-the-loop » humans cannot distinguish temporal difference < 100 ! receive incoming messages & user inputs update state of remote milliseconds (denotation and explosion) vehicles » places constraints on communication latency of simulation ! update local display platform ! for each local vehicle » compute (integrate) new state over current time period 9 » send messages (e.g., broadcast) indicating new state Maria Hybinette, UGA Typical Sequence Summary visual display � 3 � 6 � 7 � 4 � 8 � 1. Detect trigger press � Image � Other Vehicle � network � 2. Audio “ fire ” sound � Generator � State Table � interface � ! Distributed Virtual Environments have 3. Display muzzle flash � terrain � different requirements compared to analytic database � control/ � 4. Send fire PDU � own vehicle � sound � simulations, leading to different solution display � dynamics � generator � interface � 5. Display muzzle flash � approaches 1 � 2 � 6. Compute trajectory, � » May be acceptable to sacrifice accuracy to achieve Controls/panels � display tracer � better visual realism 7. Display shell impact � » Limits of human perception can often be exploited visual display � 5 � 9 � 4 � 8 � 11 � 8. Send detonation PDU � ! Distributed Interactive Simulation (DIS) 9. Display shell impact � representative of approach used in building Image � Other Vehicle � network � Generator � State Table � interface � DVEs 10. Compute damage � terrain � 11. Send Entity state PDU � database � control/ � own vehicle � sound � indicating damage � display � dynamics � generator � interface � 12 10 � Maria Hybinette, UGA Controls/panels �

Outline ! Basic Dead Reckoning Model (DRM) » Generating state updates PDES: Distributed Virtual Environments » Position extrapolation Dead Reckoning ! Refinements » Time compensation » Smoothing 14 Maria Hybinette, UGA Maria Hybinette, UGA Distributed Simulation Example Communication Requirements Player Player Player Player 1 2 3 … � N ! Virtual environment simulation containing two moving vehicles ! One vehicle per federate (simulator) ! Each vehicle simulator must track location of ! Multiple players on 10 Mbits/sec Ethernet LAN other vehicle and produce local display (as ! DIS: PDU contains 144 bytes ( 1152 bits) seen from the local vehicle) ! Each vehicle generates position update every 1/30 th second (33msec) » 34,560 bits per second ! Approach 1: Every 1/30 th of a second: ! Upper bound: support 289 entities ( 10x10 6 /34,560 ) » Each vehicle sends a message to other vehicle ! Above is very optimistic indicating its current position » Cannot utilize all of the Ethernet ’ s bandwidth » Each vehicle receives message from other vehicle, » Entities generate other PDUs (e.g., weapon fires) updates its local display » Multiple entities per human player (synthetic forces) ! 56 Kbits/sec modem: at best, only one vehicle! 15 16 Maria Hybinette, UGA Maria Hybinette, UGA Issues ! http://www.worldwidewords.org/qa/qa- ! Requires generating many messages if there dea7.htm are many vehicles; we need ways to economize on communication bandwidth ! Position information corresponds to location when the message was sent; doesn ’ t take into account delays in sending message over the network Dead reckoning is one technique that attempts to address each of these issues 17 18 Maria Hybinette, UGA Maria Hybinette, UGA