2 - The Portal Language

Table of Contents

• 2.1 Objects and Interactions Supported by VR-Exchange
• 2.2 Translating Objects and Interactions to the Portal Language
• 2.3 Identifying Objects
• 2.4 Translating Attributes

2.1 Objects and Interactions Supported by VR-Exchange

The Portal provides a framework for creating objects (which have state) and interactions (event messages) that pass through a distributed messaging system. VR-Exchange provides many object and interaction classes in the Portal language. The Portal language is defined in the libPortal library. The table lists the objects and interactions supported by the Portal language.

Object and Interactions Supported by the Portal Language
Object/Interaction	libPortal Class
Acknowledge	DtPortalAcknowledgeInteraction
Action Request	DtPortalActionRequestInteraction
Action Response	DtPortalActionResponseInteraction
Aggregate	DtPortalAggregate
Application Specific	DtPortalApplicationSpecificInteraction
Collision	DtPortalCollisionInteraction
Comment	DtPortalCommentInteraction
Create Entity	DtPortalCreateEntityInteraction
Data	DtPortalDataInteraction
Data Query	DtPortalDataQueryInteraction
Designator	DtPortalDesignatorObject
Detonation	DtPortalDetonationInteraction
Emitter System	DtPortalEmitterSystemObject
Entity State	DtPortalEntity
Environment Process	DtPortalEnvironmentProcessObject
Event Report	DtPortalEventReportInteraction
Fire	DtPortalFireInteraction
Generic Interaction	DtPortalGenericInteration
Generic Object	DtPortalGenericObject
Gridded Data	DtPortalGriddedDataObject
IFF	DtPortalIffObject
Radio Receiver	DtPortalRadioReceiverObject
Radio Signal	DtPortalRadioSignalInteraction
Radio Transmitter	DtPortalRadioTransmitterObject
Remove Entity	DtPortalRemoveEntityInteraction
Set Data	DtPortalSetDataInteraction
Start	DtPortalStartInteraction
Stop	DtPortalStopInteraction

Objects and interactions have attributes that describe their state, such as location, type, velocity, and target. Each attribute is a unique data field transmitted in a protocol-independent way. That means attributes cannot always be directly copied into Portal messages.

The Portal framework allows you to create new types of objects and interactions. Brokers can create, update, and delete objects, and send interactions to the Portal. They can also subscribe to the objects and interactions they want to receive from the Portal.

If you add a new object type you do not have to recompile all brokers, only those brokers that need to translate the new object type.

2.2 Translating Objects and Interactions to the Portal Language

The job of a broker is to translate object and interaction message attributes from the broker's simulation standard to the Portal language. The translation process involves the following:

• Managing object names
• Managing update times and rates
• Converting units
• Computing default values for unspecified attributes.

Each of these issues is highly protocol-dependent. The following sections provide a general description of how VR-Exchange's data exchange represents objects and attributes. For details, refer to the class documentation.

2.3 Identifying Objects

The Portal identifies each object by a string. The string must be unique, but this is not enforced by the Portal. Future versions of the Portal may choose to enforce this. For protocols that do not identify objects by a string, some form of conversion must be developed by the broker architect.

In the default HLA broker, objects are identified by their HLA object name.

2.4 Translating Attributes

The attribute representations used by the Portal language draw heavily on the data types used by the DIS protocol. For example, Entity Location is transmitted as three doubles: X, Y, and Z, using geocentric coordinates. This method of defining location was chosen because it is widely used by both DIS and the RPR FOM, as well as most RPR FOM variants. FOMs or protocols that use geodetic (latitude, longitude, and altitude) locations must convert to geocentric coordinates before updating location data in the Portal.

All enumeration attributes use values defined in SISO-REF-010-2005, the Enumerations document used for both DIS and the RPR-FOM. The Portal uses a macro called DtDEC_ATTRIBUTE to declare attributes for objects and interactions. For example, an attribute called DamageState might be declared like this:

DtDEC_ATTRIBUTE(DtU32, DamageState, damageState);

Note

This macro resets the access level to protected. It is recommended that classes group this macro usage in one place, then set the access level as needed.

This macro will create two public functions like this:

DtU32 damageState() const { return myDamageState;}
void setDamageState(const DtU32 &val) { myDamageState = val;}

and a protected variable called:

DtU32 myDamageState; 

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