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system simulation process between every simulation node. In addition, it should make
sure of space consistency in whole, that means all simulation nodes are running on the
same battlefield terrain and the environment database, Real time rendering of virtual
scene of each node according to the received simulation entity space position and at-
titude data. According to the principle of persistence of vision, to achieve human
feeling relatively smooth on visual effect, the virtual scene rendering frame rate should
at least reach 24 frame / sec.
3.2
Current Problem
Because of the increasing of simulation node, the main problem in DIS is that the real
time communication is not ideal enough. Its main cause is that DIS just supports a
single broadcast data communication which is based on non-connect. Its features are:
(1) It cannot ensure the data sending and receiving accurately.
(2) Data sending uses the way of non-connect broadcast to send interaction informa-
tion on network ignoring whether the other simulation node needs these information.
(3) Other on line nodes can only passively receive interaction information from
network, then decides how to deal with these information.
The fault of this way is that the receiver should receive all information from network
first, then judge whether the information affects itself, process valuable information
and delete useless information. The study shows that information interaction quantity
between simulation node will increase exponentially with the increasing of the entity
number of simulation.
In summary, network bandwidth is occupied by mass unnecessary data transmitting,
this is the main reason that causes the unsatisfying real time in DIS. DIS and HLA are
short of a mechanism to confirm the communication target. If we can find a way to let
every node to communication with related node, the communication flow will be ef-
fectively decreased, and we can aim at the improving of real time in simulation.
3.3
Solution of MMO in DIS Visual Simulation
The network load brought by the great communication flow is the cause of the delayed
communication. The key problem is how to reduce the network load. In DIS, so many
entities need to communicate with each others, we can consider this problem from two
aspects: first, should these entities need to communicate? Second, how can we reduce
the communication flow during interaction? Based on those considerations, we should
concentrate on the effect of decreasing communication flow, and improve the network
communication and the virtual scene real-time rendering.
(1) Using the visual field partition interaction range to confirm the interaction ob-
jects of every entity
The military simulation is different from network game. In network game, the plays
are regarded as equal distribution, and have the same visual field. So, we can use the
nine-rectangle-grid mode and use the space dividing technology to confirm the inte-
raction objects to reduce the interaction flow. But in DIS, different simulation entity
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