Distributed Virtual Environment and Simulation Package

1
Distributed Virtual Environment and Simulation
Package

• Stephen Lawrence
• stevel_at_cc.gatech.edu

2
Overview of Topics

• Type of Simulation
• Federation Organization
• Class Organization
• Internals of some DVESIM classes
• Creating a Federate
• Creating Simulation Objects

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Type of Simulation

• Object Based Simulation (using c)
• Simulator, object(such as a tank or projectile),
  and battlefield classes
• new object types are created by sub-classing
  existing objects
• Event Driven
• Classes define event handlers to process events
• Federated (using DRTI)
• Each federate has local and non-local entities
• object updates are only send when needed
• Messages are sent between user and entities

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Federation Organization
UI Federate
UI Federate
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Federation Organization (cont)

• Simulator Federates
• Each controls a number of objects within the
  simulation world
• Sends and received updates and interactions
  concerning its objects, and objects controlled
  by other federates
• UI Federates
• Allows users to view and interact with object in
  the Federation

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Class Organization
Simulator Federate Classes
Structure
Entity
Projectile
subclass
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Internals Simulator ClassEach simulator
federate runs one instance of the simulator class

• Manages Event Queue
• Schedules events
• Dispatches events to objects
• Simulates Battlefield
• Collision/proximity detection
• Projectile detonation
• Federate communication
• sends and receives events such as object updates
  and messages

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Internals Simulator Class (continued)
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Internals Simulator Class (continued)

• Simulation Class Execution
• init()
• Schedule all new object events for all local
  objects.
• Sets up simulation state
• schedules first new state event
• run()
• while event-queue not empty
• process event
• deliver event to object if necessary
• finishUp()

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Internals Simulator Class Example

• The federates executive function removes the tick
  event from the event queue.
• The tick event is passed to the federates tick
  event handler (a method of it's simulator class).
  
• The tick event is forwarded, by the simulators
  event handler, to all objects in the battlefield.
  
• The simulator class checks for collision between
  it's local objects and all objects in the
  battlefield (local and foreign).
• A new tick event is created and scheduled for
  some small time in the future.

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Internals Battlefield Class

• Manages objects
• objects hashed by RTIObjectHandle for fast
  access
• Provides means for objects to access other
  objects
• Contains both locally controlled objects, and
  objects controlled by other federates.
• Terrain Information (not implemented)
• provides terrain type for given coordinates on
  the battlefield
• objects view the world in only two dimensions,
  the battlefield provides additional elevation and
  slope information when needed

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Internals Event Class

• Stores Event Information (TimeStamp, details)
• Tick Event -gt triggers location updates and
  collision detection
• New Object Event -gt adds a new object to the
  battlefield
• Order Event -gt sends object and simulation
  messages, such as orders, simulation over, etc
• Other Events
• Movement Event, Collision Event, Proximity
  Event,Detonation Event, User Defined Events

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Internals Event Class Example

• Collision event is passed to the event handler by
  the executive function when it is safe to
  process.
• The event handler passes the collision event to
  the local object involved in the collision (if
  two local objects are in collision, each will get
  it's own event).
• The object reacts to the collision event. The
  default action is to do nothing, but subclasses
  of the object type can redefine the event
  handlers to do something interesting, such as
  stop, change direction, or calculate a new path.

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Internals Object Class

• Physical State Information (location, velocity,
  acceleration)
• Processes New State events to update its
  physical state
• Entity Subclass
• Provides basic movement services (set
  heading/location, etc)
• Fires projectiles

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Internals Object Class (continued)

• Object Class Execution
• A new object is created and stored in new object
  event
• The simulator later processes new object event
• Calls object init() function
• Sends New State and other events to object
• Object is removed by a call to exitObject()
• objects finishUp() function is called, and the
  object is deleted

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Internals Object Class Example

• Simulator federate 1 schedules schedules a new
  object event for object A at time 1, register's
  an object instance for it within the federation,
  and sends an attribute update for the the object
  with timestamp 1
• Simulator federate 2 discovers the object,
  creates a new object instance, and puts it in a
  temporary holding place.
• When requesting a Next Event Request for time 1,
  federate 2's RTI ambassador delivers the
  attribute update for object A
• Federate 2, now having received the first
  attribute information about object A, schedules a
  new object event with timestamp 1, which will be
  processed to add object A to it's battlefield.
• After completing a Next Event Request for
  timestep 1, federate 1 will be able to process
  it's new object event and add object A to it's
  battlefield.

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Internals Visualization

• Displays all the objects in the federation
• Paces the simulation with wallclock time
• Allows user to send messages to the objects
  (entities)