Nasal Flightplan

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:

• flightplan() - return the active plan.
• airwaysRoute()
• createFlightplan() - creates new empty plan. A path can be supplied to load a plan from xml.

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 "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()

This is used for graphical display: it’s an array of coordinates which show the path of the plan. This includes holds, procedure turns, turn anticipation and more.

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, setting empty type is same as setting "at". See below for type list.

setAltitude(altitude, type)

Sets the altitude restriction. Setting nil type, will crash FG, setting empty type is same as setting "at". See below for type list.

path()

Returns a vector of hashes containing lat and lon variables. These compromise a curved path for long non straight legs.

courseAndDistanceFrom(coord)

Return vector with true course and distance. Coord is a geo.Coord.

parents

Nasal parents.

wp_owner

Will return you the owning route-structure of the WP - this could be an airway, procedure, or the flightplan if the waypoint doesn’t belong to a route structure.

index

Returns the index of the leg in the owning route-structure.

alt_cstr

Read-only. Altitude restriction.

alt_cstr_type

Read-only. Altitude restriction type. See below for list.

speed_cstr

Read-only. Speed restriction.

speed_cstr_type

Read-only. Speed restriction. See below for list.

leg_distance

Returns distance along the leg, from the preceding waypoint.

leg_bearing

Returns the bearing along the leg.

distance_along_route

Return the total distance laterally along the route to the beginning of the leg.

For speed restrictions these types can be used:

• "at" = kt should be spot on
• "above" = kt should be higher
• "below" = kt should be under
• "computed" = predicted kt
• "computed-mach" = predicted mach
• "mach" = its in mach instead of kt
• "delete" = Cleared by ATC

For altitude restrictions these types can be used:

• "at" = alt should be spot on
• "above" = alt should be higher
• "below" = alt should be below
• "computed" = predicted alt
• "computed-mach" = not used for altitude
• "mach" = not used for altitude
• "delete" = Cleared by ATC

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>) );

Related content

Wiki articles

• Nasal library § Extension functions
• Navdata cache § Accessing via Nasal
• Route Manager
• Route Manager internals
• Howto:Control the route manager in Nasal

Documentation

• flightplanGhostSetMember — Members of a flight plan object that can be set.
• flightplanGhostGetMember — Members of flight plan object that can be read.
• initNasalPositioned — Contains a list of functions that can be called on airport, flight plan, waypoint, procedure, or flight plan leg objects.
• FGRouteMgr::FGRouteMgr — List of fgcommands relating to the route manager.

Misc

• https://sourceforge.net/p/flightgear/mailman/message/34688624/
• https://sourceforge.net/p/flightgear/mailman/message/35164289/
• https://sourceforge.net/p/flightgear/mailman/flightgear-devel/thread/BB67C9F3-028B-40E5-94E4-246CD1E0B2CC%40mac.com/#msg23708827
• https://sourceforge.net/p/flightgear/mailman/message/33699574/
• https://sourceforge.net/p/flightgear/mailman/message/21010010/
• https://sourceforge.net/p/flightgear/mailman/message/23678747/

Threads

References