Nasal Flightplan

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Note  Whenever possible, please refrain from modeling complex systems, like an FDM, autopilot or Route Manager with Nasal. This is primarily to help reduce Nasal overhead (especially GC overhead). It will also help to unify duplicated code. The FlightGear/SimGear code base already contains fairly generic and efficient systems and helpers, implemented in C++, that merely need to be better generalized and exposed to Nasal so that they can be used elsewhere. For example, this would enable Scripted AI Objects to use full FDM implementations and/or built-in route manager systems.

Technically, this is also the correct approach, as it allows us to easily reuse existing code that is known to be stable and working correctly, .

For details on exposing these C++ systems to Nasal, please refer to Nasal/CppBind. If in doubt, please get in touch via the mailing list or the forum first.


Because FlightGear's route manager flight plan system is exposed to Nasal, Nasal can be used to interact with flight plans. Obviously, this is very useful, especially for aircraft like airliners, which have complex route managers systems. This article shows how this can be done.

Background

The Nasal functions relating to the route manager system include:

Flight plans are based on waypoints, which, in C++, inherit from the FGPositioned (doxygen) class.

Waypoint hashes

The following are members of a waypoint ghost, as generated by, for example, airwaysRoute() :

wp_name 
Name of the waypoint, returned as string.
wp_type 
Waypoint type, returned as string. One of "basic," "navaid," "offset-navaid," "runway," "hdgToAlt," "dmeIntercept," "radialIntercept," or "vectors."
wp_role
Role of waypoint.
wp_lat or lat 
Latitude of waypoint.
wp_lon or lon 
Longitude of waypoint.
wp_parent_name 
Name of waypoint's parent.
wp_parent 
Waypoint's parent.
fly_type 
How to waypoint should be flown over or reacted to. One of "Hold," "flyOver," or "flyBy."
heading_course 
Heading of runway.

Flightplan methods and variables

Notice that instead of passing a leg as parameter, a waypoint can be passed.

getWP(index) 
Returns the leg for specified index.
currentWP() 
Return current active leg.
nextWP() 
Make next waypoint active.
getPlanSize() 
Returns number of waypoints
appendWP(leg) 
Add a leg to the end of the flightplan.
insertWP(leg, index) 
Pass a leg object and its position.
deleteWP(index) 
Deletes the waypoint at specified index.
insertWPAfter() 
insertWaypoints(vector, index) 
Pass a vector of waypoint objects, and the position to insert.
cleanPlan() 
Clears all waypoints except destination and departure.
clearWPType(type) 
Supply a type string, it will clear all waypoints of the type.
clone() 
Return a copy of the flightplan.
pathGeod() 
finish() 
Finish the plan. (a call to delegate will be made)
indexOfWP(wp) 
Returns the index of the passed waypoint/leg.
destination 
airport object as destination.
destination_runway 
rwy object as destination and its airport implicit.
departure 
airport object as departure.
departure_runway 
rwy object as departure and its airport implicit.
id 
optional name of plan.
sid 
procedure object for SID.
star 
procedure object for STAR.
sid_trans 
star_trans 
approach 
procedure object for approach.
current 
Index of current waypoint.
aircraftCategory 
ICAO aircraft category.
followLegTrackToFix 
Specific used by some procedures. It controls whether the system will fly on an intersection course (and hence, different track) to the end of the leg, or make a corrective S-turn to get back on the leg track immediately it becomes possible.
activate() 
This will make the flight plan the default (the one used in route-manager).
save(path) 
Save a plan to xml. Will return true or false for success.

Leg methods and variables

A leg is a wrapper for a waypoint, so it will have all waypoints variables and methods plus what is listed below. Notice, that a leg you have gotten from a plan, but deleted in the plan, will be invalid and should not be used or modified. A leg you have gotten from a plan, when modified, will modify the leg inside the plan you got it from.

setSpeed(speed, type) 
Sets the speed restriction. Setting nil type, will crash FG.
setAltitude(altitude, type) 
Sets the altitude restriction. Setting nil type, will crash FG.
path() 
courseAndDistanceFrom() 
parents 
index 
alt_cstr 
Read-only. Altitude restriction.
alt_cstr_type 
Read-only. Altitude restriction type. Can be "at", "above", "below", "mach", "computed", "computed-mach", "delete".
speed_cstr 
Read-only. Speed restriction.
speed_cstr_type 
Read-only. Speed restriction. Can be "at", "above", "below", "mach", "computed", "computed-mach", "delete".
leg_distance 
leg_bearing 
distance_along_route 

Procedure methods and variables

route(runway) 
Returns a vector of waypoints.
transition() 
Only works on STAR and SID.

Examples

# get the active flight plan (the one being used by the route manager)
var fp = flightplan();

# or create one an XML file
fp = flightplan('/path/to/xml');

# save the active flight plan
fgcommand("save-flightplan", props.Node.new({"path": 'path/to/xml'}));

# duplicate a flight-plan
var secondary = fp.clone();

var dest = airportinfo('KSFO');
var rwy = dest.runway('19L');
# the the arrival runway (and airport, automatically)
fp.destination_runway = rwy;

# or if no runway is known/specified
fp.destination = dest;

Building procedures and transitions. As mentioned above there's a couple of different ways to handle this, the examples below assume the C++ code automatically deletes and re-inserts waypoints for procedures, but that's only one possible design.

var apt = airportinfo('KSFO');
# example for SIDs, STARs are the same, approaches too
var allSids = apt.sids();

# SIDs for a specific runway - note these return SID IDs as string, for compatibility with existing code
var rwySids = apt.sids('28L');

Inserting and deleting waypoints (possibly in batches)

var fp = flightplan();
# waypoint created from lat, lon, or a navaid, or anything else?
var pos = geo.aircraft_position().apply_course_distance(getprop("/orientation/heading-deg"), 100000);
var wp = createWP(pos.lat(), pos.lon(), "EPICA");

# manually insert a waypoint at the end of the plan
fp.insertWP(wp, fp.getPlanSize());

# manually insert a waypoint at a defined position (n) into the plan
fp.insertWP(wp, n);

# route along airways, and insert a whole bunch of waypoints
# this is needed for the route-manager dialog, maybe not for a
# real FMS interface....
var segment = [<waypoint object>, <waypoint object>, <waypoint object>];
# segment is a vector of waypoints now
fp.insertWaypoints(segment, fp.getPlanSize());

aircraft.history() (3.2+)

Function to expose flight history as aircraft.history()

var hist = aircraft.history();

# get history of aircraft position/orientation collapsing
# nodes with a distance smaller than the given minimum
# edge length
debug.dump( hist.pathForHistory(<minimum-edge-length-meter>) );

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