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8 KiB
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195 lines
No EOL
8 KiB
HTML
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<HEAD></HEAD>
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<h3>Using AI objects in FlightGear</h3><hr>
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<br><br>
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Starting with FlightGear version 0.9.4 you can place AI objects in the "FlightGear world".
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In version 0.9.4 the AI objects can be defined in the <b><tt>preferences.xml</tt></b> file, or
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in an airplane's <b><tt>*-set.xml</tt></b> file. In later versions of FlightGear they are
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defined in a "scenario file" only. Types of AI objects available are ships, airplanes,
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thunderstorms, thermals, aircraft carriers, static and ballistic objects.
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<BR><BR>
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AI objects have some things in common: The have a location in the "FlightGear world",
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they can have an associated exterior 3D model, and they can move according to an internal
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FDM (flight dynamics model). As of now, these objects are created at simulator start-up
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by adding some XML code to a scenario file. The scenario file must be in the
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<b><tt>data/Data/AI</tt></b> directory. You select which scenario file you want to use by naming
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it in the <b><tt>preferences.xml</tt></b> file. (Note: As with everything in the
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<b><tt>preferences.xml</tt></b> file, the entries can be overridden by an aircraft's
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<b><tt>*-set.xml</tt></b> file, or at the command line.) The <b><tt>preferences.xml</tt></b>
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file has an entry that looks like this (FlightGear versions newer than 0.9.4):
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<BR><BR>
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<b><tt>
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<ai><br>
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<enabled type="bool">true</enabled><br>
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<scenario>demo_scenario</scenario><br>
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</ai><br>
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</tt></b>
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<BR><BR>
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The scenario contains one entry for each AI object. The entry specifies what kind of
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object to create, what it's initial conditions will be, and optionally (for aircraft and
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ships) a flight plan.
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<BR><BR><BR>
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<h3>Ships</h3><hr>
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The entry to create a sailboat would look like this:
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<br><br>
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<b><tt>
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<entry><br>
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<type>ship</type><br>
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<path>AI/Aircraft/sailboat1/sailboat.xml</path><br>
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<speed type="double">12.0</speed><br>
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<altitude type="double">0.0</altitude><br>
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<longitude type="double">-122.33333</longitude><br>
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<latitude type="double">37.61667</latitude><br>
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<heading type="double">20.0</heading><br>
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<rudder type="double">-3.0</rudder><br>
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</entry><br>
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</tt></b>
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<BR><BR>
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Most of the entries are self-explanatory. The "type" of object can be one of "aircraft",
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"ship", "storm", "thermal", "carrier", "static" or "ballistic". The rest of the items
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give the AI object a model, a starting location, and a starting speed and direction. You
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use the <b><path></b> item to give the object any valid exterior model. You can even
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make the ship look like an airplane if you want! The "ship" type can also have a
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<b><rudder></b> value specified, which will cause the ship to move in a circle
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(HINT: use small values, five degrees or less, and right rudder is positive).
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<BR><BR>
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<h3>Aircraft</h3><hr>
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Here is an example of how to create an aircraft AI object:
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<BR><BR>
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<b><tt>
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<!-- puts an A-4 north of KSFO, orbiting at 7000 ft --><br>
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<entry><br>
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<type>aircraft</type><br>
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<class>jet_fighter</class><br>
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<path>Aircraft/a4/Models/a4-blue.xml</path><br>
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<speed type="double">320.0</speed><br>
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<altitude type="double">7000.0</altitude><br>
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<longitude type="double">-122.6</longitude><br>
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<latitude type="double">37.9</latitude><br>
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<heading type="double">210.0</heading><br>
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<roll type="double">-15.0</roll><br>
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</entry>
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</tt></b>
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<BR><BR>
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It looks much the same as the ship AI code. There are two differences, the
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<b><class></b> item and the <b><roll></b> item. If the class is set to
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"tanker" the airplane will allow you to refuel if you can get close behind it (so far
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supported by JSBSim only) The "roll" will cause the airplane to fly in a circle. In the
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above example the A-4 will be orbiting to the left at 15 degrees of bank. You can also
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create a ship or airplane with a flight plan. In this case the object will follow the
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flight plan and then delete itself when it reaches the end, or (new since version 0.9.8)
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the object can be set to endlessly repeat a flight plan. The flight plans are located in
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<b><tt>data/Data/AI/FlightPlans</tt></b>. To create an airplane with a flightplan do this:
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<BR><BR>
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<b><tt>
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<entry><br>
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<type>aircraft</type><br>
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<class>jet-transport</class><br>
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<path>Aircraft/737/Models/737.xml</path><br>
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<flightplan>KSFO_ILS28L.xml</flightplan><br>
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</entry><br>
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</tt></b>
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<BR><BR>
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In this case you don't need to specify initial conditions because they are already defined
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in the flight plan. The AI aircraft objects can be displayed on radar. See the
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<b><tt>Aircraft/Instruments/radar.xml</tt></b> file for details.
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<BR><BR>
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<h3>Thunderstorms</h3><hr>
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<BR>
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To make a thunderstorm, use this:
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<BR><BR>
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<b><tt>
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<!-- puts a thunderstorm overhead OSI (Woodside VOR) --><br>
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<entry><br>
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<type>storm</type><br>
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<path>Models/Geometry/thunderstorm.xml</path><br>
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<speed type="double">20.0</speed><br>
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<altitude type="double">4000.0</altitude><br>
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<latitude type="double">37.3917</latitude><br>
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<longitude type="double">-122.2817</longitude><br>
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<heading type="double">90</heading><br>
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</entry><br>
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</tt></b>
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<BR><BR>
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There's not much to it. No, they don't turn :) New since version 0.9.8 is the ability
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to add lightning and turbulence to a thunderstorm. For an example of this see the scenario
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file called "bigstorm_demo.xml". The AI storm objects can be displayed on weather radar. See the
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<b><tt>Aircraft/Instruments/wxradar.xml</tt></b> file for details.
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<br><br>
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<h3>Thermals</h3><hr>
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<BR>
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To create a thermal, use this:
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<BR><BR>
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<b><tt>
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<!-- puts a thermal over the control tower at KSFO --><br>
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<entry><br>
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<type>thermal</type><br>
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<latitude type="double">37.61633</latitude><br>
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<longitude type="double">-122.38334</longitude><br>
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<strength-fps type="double">8.33</strength-fps><br>
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<diameter-ft type="double">4000.0</diameter-ft><br>
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<height-msl type="double">6000.0</height-msl><br>
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</entry><br>
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</tt></b>
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<BR><BR>
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The AI thermals don't move, they are invisible, and they don't "lean" downwind.
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The <b><strength-fps></b> defines the maximum vertical velocity of the airmass
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at the center of the thermal. The strength decreases to zero at the thermal's edge.
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<b><height-msl></b> defines the top of the thermal.
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<br><br>
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<h3>Ballistic objects</h3><hr>
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<br>
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A ballistic AI object starts with an initial location, azimuth, elevation and speed, then
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follows a ballistic path from there (with air resistance included). Try this:
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<BR><BR>
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<b><tt>
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<entry><br>
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<type>ballistic</type><br>
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<path>Models/Geometry/rocket.xml</path><br>
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<speed type="double">500.0</speed><br>
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<altitude type="double">50.0</altitude><br>
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<longitude type="double">-122.39</longitude><br>
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<latitude type="double">37.62</latitude><br>
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<heading type="double">200.0</heading><br>
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<azimuth type="double">70.0</azimuth><br>
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<elevation type="double">45.0</elevation><br>
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</entry><br>
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</tt></b>
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<BR><BR>
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There is not much call for rocket launches in FlightGear, but the ballistic AI object is
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the basis for FlightGear's <a href="README.submodels">submodels</a> system.
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<BR><BR><BR>
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<h3>Aircraft Carriers</h3><hr>
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<br>
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The aircraft carrier AI object is based on the "ship" object but is much more complicated.
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See the scenario file called <b><tt>nimitz_demo.xml</tt></b> for details.
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<BR><BR><BR>
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<hr>
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Dave Culp, updated 23 Oct 2005<br>
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davidculp2@comcast.net
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</HTML> |