I promised the folks on IRC last night that I would clean up and post my
multiplayer target tracking script.
In short, this script will manipulate your autopilot target settings
(speed, altitude, and heading) to track any multiplayer or "ai" aircraft
(entity) that is active in your system.
It's cheating I know, and a good pilot could do a much better job
tracking a target manually, but it's a fun diversion and helps us less
skilled pilots keep those little targets closer and more visible for
longer periods of time.
The installation instructions are located at the start of the attached
script, but I will repeat them here:
# 1. Copy this file into $FGROOT/data/Nasal (along with the other
# system nasal scripts.)
#
# 2. Start up FlightGear selecting an airplane with a reasonably configured
# autopilot that responds to and works with the standard autopilot
# dialog box (F11). The MiG 15 is one that works, the 777-200 works,
# the Citation Bravo does not work, the default c172 probably does not
# work, etc.
#
# 3. Take off and establish stable flight.
#
# 4. Open the property browser (File->Browse Internal Properties) and
navigate
# to /ai/models/ Choose one of the available aircraft[] or multiplayer[]
# entries. You can look at all those subtrees to find the call sign you
# want. Also note that the subtree for each entity has a radar
section that
# will show range and offset from your current heading.
#
# 5. Open a second property browser window (upper left click box in the
first
# property browser window.) Navigate to /autopilot/target-tracking/
#
# 6. Set "/autopilot/target-tracking/target-root" to point to the entity
# path you discovered in step #4. For instance, this should be set to
# something like /ai/models/multiplayer[2] or /ai/models/aircraft[0]
#
# 7. Set "/autopilot/target-tracking/goal-range-nm" to the follow distance
# you want.
#
# 8. Set "/autopilot/target-tracking/enable" = 1, this will turn on the
radar
# computation for each ai/multiplayer entity and will tell the tracking
# script to start updating the autopilot settings.
#
# 9. Open up the autopilot configuration window (F11) and activate any
of the
# heading, pitch, and speed axes. The script will begin updating the
heading
# bug angle, the "speed with throttle" value, and the "altitude hold"
value.
#
# 10. You can choose to mix and match any of the autopilot modes you
want, i.e.
# you could turn off the heading control and turn manually while the
system
# holds speed and altitude for you. (This might be useful if your
target is
# turning tighter than the 30 degree max bank angle the autopilot
will do.)
#
# 11. It always helps to have a sensible target arcraft to chase. You are
# flying within the turn radius and climb rate limits of your autopilot.
#
# Don't forget you are pilot in command and at all times responsible for
# maintaining safe airspeed and altitude.
#
# Enjoy the ride!
Curt.
--
Curtis Olson http://www.flightgear.org/~curt
HumanFIRST Program http://www.humanfirst.umn.edu/
FlightGear Project http://www.flightgear.org
Unique text: 2f585eeea02e2c79d7b1d8c4963bae2d
# This is a small script that adjusts autopilot target values to track
# (fly in formation with) an AI or Multiplayer aircraft.
# Quick start instructions:
#
#
# 1. Copy this file into $FGROOT/data/Nasal (along with the other
# system nasal scripts.)
#
# 2. Start up FlightGear selecting an airplane with a reasonably configured
# autopilot that responds to and works with the standard autopilot
# dialog box (F11). The MiG 15 is one that works, the 777-200 works,
# the Citation Bravo does not work, the default c172 probably does not
# work, etc.
#
# 3. Take off and establish stable flight.
#
# 4. Open the property browser (File->Browse Internal Properties) and navigate
# to /ai/models/ Choose one of the available aircraft[] or multiplayer[]
# entries. You can look at all those subtrees to find the call sign you
# want. Also note that the subtree for each entity has a radar area that
# will show range and offset from your current heading.
#
# 5. Open a second property browser window (upper left click box in the first
# property browser window.) Navigate to /autopilot/target-tracking/
#
# 6. Set "/autopilot/target-tracking/target-root" to point to the entity
# path you discovered in step #4. For instance, this should be set to
# something like /ai/models/multiplayer[2] or /ai/models/aircraft[0]
#
# 7. Set "/autopilot/target-tracking/goal-range-nm" to the follow distance
# you want.
#
# 8. Set "/autopilot/target-tracking/enable" = 1, this will turn on the radar
# computation for each ai/multiplayer entity and will tell the tracking
# script to start updating the autopilot settings.
#
# 9. Open up the autopilot configuration window (F11) and activate any of the
# heading, pitch, and speed axes. The script will begin updating the heading
# bug angle, the "speed with throttle" value, and the "altitude hold" value.
#
# 10. You can choose to mix and match any of the autopilot modes you want, i.e.
# you could turn off the heading control and turn manually while the system
# holds speed and altitude for you.
#
# 11. It always helps to have a sensible target arcraft to chase. You are
# flying within the turn radius and climb rate limits of your autopilot.
#
# Don't forget you are pilot in command and at all times responsible for
# maintaining safe airspeed and altitude.
#
# Enjoy the ride!
print("Target Tracking script loading ...");
# script defaults (configurable if you like)
default_update_period = 0.05;
default_goal_range_nm = 0.05;
default_target_root = "/ai/models/aircraft[0]";
default_min_speed_kt = 120;
# master enable switch
target_tracking_enable = 0;
# update period
update_period = default_update_period;
# goal range to acheive when following target
goal_range_nm = 0;
# minimum speed so we don't drop out of the sky
min_speed_kt = 0;
# Target property tree root
target_root = "";
# Initialize target tracking
TrackInit = func {
target_tracking_enable = getprop("/autopilot/target-tracking/enable");
if ( target_tracking_enable == nil ) {
target_tracking_enable = 0;
setprop("/autopilot/target-tracking/enable", target_tracking_enable);
}
update_period = getprop("/autopilot/target-tracking/update-period");
if ( update_period == nil ) {
update_period = default_update_period;
setprop("/autopilot/target-tracking/update-period", update_period);
}
goal_range_nm = getprop("/autopilot/target-tracking/goal-range-nm");
if ( goal_range_nm == nil ) {
goal_range_nm = default_goal_range_nm;
setprop("/autopilot/target-tracking/goal-range-nm", goal_range_nm);
}
min_speed_kt = getprop("/autopilot/target-tracking/min-speed-kt");
if ( min_speed_kt == nil ) {
min_speed_kt = default_min_speed_kt;
setprop("/autopilot/target-tracking/min-speed-kt", min_speed_kt);
}
target_root = getprop("/autopilot/target-tracking/target-root");
if ( target_root == nil ) {
target_root = default_target_root;
setprop("/autopilot/target-tracking/target-root", target_root);
}
}
settimer(TrackInit, 0);
# If enabled, update our AP target values based on the target range,
# bearing, and speed
TrackUpdate = func {
# refresh user configurable values
target_tracking_enable = getprop("/autopilot/target-tracking/enable");
update_period = getprop("/autopilot/target-tracking/update-period");
goal_range_nm = getprop("/autopilot/target-tracking/goal-range-nm");
target_root = getprop("/autopilot/target-tracking/target-root");
if ( target_tracking_enable == 1 ) {
# force radar debug-mode on (forced radar calculations even if
# no radar instrument and ai aircraft are out of range
setprop("/instrumentation/radar/debug-mode", 1);
my_hdg_prop = sprintf("/orientation/heading-magnetic-deg" );
my_hdg = getprop(my_hdg_prop);
alt_prop = sprintf("%s/position/altitude-ft", target_root );
alt = getprop(alt_prop);
if ( alt == nil ) {
print("bad property path: ", alt_prop);
return;
}
speed_prop = sprintf("%s/velocities/true-airspeed-kt", target_root );
speed = getprop(speed_prop);
if ( speed == nil ) {
print("bad property path: ", speed_prop);
return;
}
range_prop = sprintf("%s/radar/range-nm", target_root );
range = getprop(range_prop);
if ( range == nil ) {
print("bad property path: ", range_prop);
return;
}
h_offset_prop = sprintf("%s/radar/h-offset", target_root );
h_offset = getprop(h_offset_prop);
if ( h_offset == nil ) {
print("bad property path: ", h_offset_prop);
return;
}
if ( h_offset > -90 and h_offset < 90 ) {
# in front of us
range_error = range - goal_range_nm;
} else {
# behind us
range_error = goal_range_nm - range;
}
target_speed = speed + range_error * 100.0;
if ( target_speed < min_speed_kt ) {
target_speed = min_speed_kt;
}
setprop( "/autopilot/settings/target-altitude-ft", alt );
setprop( "/autopilot/settings/heading-bug-deg", my_hdg + h_offset );
setprop( "/autopilot/settings/target-speed-kt", target_speed );
}
# last thing to do before we return from this function
registerTimer();
}
# timer handling to cause our update function to be called periodially
registerTimer = func {
settimer(TrackUpdate, update_period );
}
registerTimer();
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