DIS Articulation

Updating the simulation from input DIS articulation

Articulated part records that are a part of entity state PDUs received by a WSF application may be used to update the state of the WSF platform that reflects the state of (shadows) the external entity. This allows locally modeled sensors to utilize the proper signature when they perform detection chances against the shadow platform.

Reflecting signature updates using articulated parts requires two sets of input:

• Additions to the platform for the shadow platform that define script variables and scripts. This information will be used by the dis_interface to inform the platform when a change has been received. (Note that this information can be included even for platforms that aren’t externally controlled. It is simply ignored for local platforms.)

• Additional dis_interface commands that define the identification of the parts to be tracked and how to inform the platform that a change has been received.

Following is a trivial example in which a 737 has landing gear. When an articulation update is received, variables will get updated and scripts called so the platform can changes its signature as needed.

Following is the additional platform_type data (all extraneous data has been omitted). ‘writeln’ statements may be omitted if desired

platform_type 737 WSF_PLATFORM
   script_variables
      double landing_gear_state    = 0.0;
   end_script_variables

   script void landing_gear_state_changed()
      writeln("T=",TIME_NOW," ",Name()," landing_gear_state_changed");
      writeln("  landing gear state: ", landing_gear_state);
      if (landing_gear_state    == 0.0)
      {
         writeln(" Change signature to landing_gear_up");
         SetRadarSigState("landing_gear_up");
      }
      else
      {
         writeln(" Change signature to landing_gear_down");
         SetRadarSigState("landing_gear_down");
      }
   end_script
end_platform

Following is the additional dis_interface data:

dis_interface
   entity_type 737           1:2:225:57:1:7:0

   entity_appearance
      type 737 articulation 3087 landing_gear_state   landing_gear_state_changed
   end_entity_appearance
end_dis_interface

The DIS standard defines articulated part 3072 as the base parameter type value for the landing gear. In this example, the ‘rotation’ parameter is being used to signify an appearance change, which means 15 must be added to the base parameter type value. Thus, the resulting parameter types value is 3087 (3072 + 15). A rotation value of zero indicates the landing gear is up while a non-zero value indicates it is down.

The processing of received articulated parts records proceeds as follows:

• If the record does not have the ‘change’ flag set, ignore the record.

• If an entity_appearance articulation entry does not exists for the platform and parameter value, ignore the record.

• Update the script variable specified on the entity_appearance articulation entry and store the script name to be called upon completion of processing of all the records.

• Once all articulation records have been processed, invoke the scripts that correspond to the variables that were changed. If multiple variables were changed that referenced the same script, the script will only be called once.

In this example, if an entity state is received in which parameter 3087 is marked as changed, the script variable ‘landing_gear_state’ will be set to the received values. Then, the script ‘landing_gear_state_changed’ will be called.

DIS Output

Any WSF articulated part (comm or sensor) can be included on the DIS entity state PDU. In addition, explicit parts can be defined for articulations not associated with a platform’s system (visual_part). Parts are controlled using the :command`_.articulated_part`.

A defined articulation then be included in the DIS output by explicitly including it in the dis_interface, as showing in the example below.

dis_interface
   articulated_part 737 landing_gear 1
      publish azimuth
   end_articulated_part

   articulated_part 737 landing_gear 2
      parent 1
      publish elevation
   end_articulated_part
end_dis_interface

The articulated_part block includes three parameters.

• A platform_type that will include the articulation in its entity state PDUs.

• The name of the articulated part on the platform_type.

• An ID to associate with the part in the DIS entity state PDU.

Contained within the block are a number of commands.

• The parent command informs DIS that a part is attached to another part. This will allow an articulation to inherit its parent’s movements.

• The publish command informs DIS that a part will publish a particular piece of information. These include:

• x - The x component of the part’s position.

• y - The y component of the part’s position.

• z - The z component of the part’s position.

• x_rate - The rate of change in the x component of the part’s position.

• y_rate - The rate of change in the y component of the part’s position.

• z_rate - The rate of change in the z component of the part’s position.

• azimuth - The rotation about the part’s z-axis.

• elevation - The rotation about the part’s y-axis.

• rotation - The rotation about the part’s x-axis.

• azimuth-rate - The rate of motion about the part’s z-axis.

• elevation-rate - The rate of motion about the part’s y-axis.

• rotation-rate - The rate of motion about the part’s x-axis.