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Initial revision of target tracking script, see script code for operating

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instructions.
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curt 2006-06-29 00:52:51 +00:00
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# 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 {
target_tracking_enable = getprop("/autopilot/target-tracking/enable");
update_period = getprop("/autopilot/target-tracking/update-period");
if ( target_tracking_enable == 1 ) {
# refresh user configurable values
goal_range_nm = getprop("/autopilot/target-tracking/goal-range-nm");
target_root = getprop("/autopilot/target-tracking/target-root");
# 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();