Route manager: Difference between revisions

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Route manager waypoints are entered as a navaid ident, an explicit latitude/longitude pair, or as an offset (bearing and distance) from another navaid. Each waypoint may also have an altitude associated with it, for vertical navigation modes (VNAV). In the future, other data, especially speed restrictions, may also be associated with waypoints.
Route manager waypoints are entered as a navaid ident, an explicit latitude/longitude pair, or as an offset (bearing and distance) from another navaid. Each waypoint may also have an altitude associated with it, for vertical navigation modes (VNAV). In the future, other data, especially speed restrictions, may also be associated with waypoints.


Example waypoint definitions:
The route-manager maintains a ''current waypoint'', which is shown in route-manager dialog, the GPS dialog (in LEG mode), on the default HUD, and potentially in cockpit displays in the aircraft. Normally, the route-manager moves automatically to the next waypoint after passing the current point (this is known as 'sequencing'), but if necessary the active waypoint can be manually adjusted.


;KJFK
An important piece of terminology is a ''leg'', which is a section of route between two waypoints. Many real-world devices deal in legs primarily, since each leg corresponds to a desired track, a distance and possibly an altitude to climb / descend. In the FlightGear route manager, the ''active leg'' is from the previous waypoint to the current waypoint - i.e the current waypoint is where you're heading to at the moment.
: airport identifier
;UW
: navaid identifier (NDB, VOR or a fix/interaction)
;TLA/210/35
: offset from a navaid - in this example, the 210-degree magnetic radial from TLA VOR, 35 nautical miles out
;WOBAD@18000
: WOBAD fix, at eighteen thousand feet altitude
;SPL/050/12.3@2000
: 12.3 nautical miles from SPL VOR on the 050 magnetic radial, at two thousand feet


==Defining a Route==
==Defining a Route==

Revision as of 10:49, 14 March 2010

A real route-manager page!

Introduction

(in the following sections, familiarity with basic IFR concepts, Autopilot usage and radio navigation is assumed)

The route-manager models part of the functionality found in real-world GPS and FMS devices, but is usable in any aircraft. Some panel instruments may provide access to the route manager via their own UI, but the route-manager is always available through a generic dialog box. The route-manager is also how a flight plan is made available to FlightGear - in the future this will hopefully permit better ATC and multi-player interactions, since ATC logic or controllers will be able to observe the filed plan associated with a pilot.

It's important to realize that the route-manager (and GPS) are pieces that a panel instrument might present as a single real world device - the mapping between C++ modules, generic user interface and in-panel instruments is very fluid, by design. In general core features exist in whichever place seems the most natural, and it's up to instruments to aggregate the core modules as they require.

Concepts

The route-manager maintains a flight-plan, consisting of departure, destination, alternate airport and cruise information, as well as a list of waypoints. All information is currently optional, which is highly unrealistic, but convenient.

Route manager waypoints are entered as a navaid ident, an explicit latitude/longitude pair, or as an offset (bearing and distance) from another navaid. Each waypoint may also have an altitude associated with it, for vertical navigation modes (VNAV). In the future, other data, especially speed restrictions, may also be associated with waypoints.

The route-manager maintains a current waypoint, which is shown in route-manager dialog, the GPS dialog (in LEG mode), on the default HUD, and potentially in cockpit displays in the aircraft. Normally, the route-manager moves automatically to the next waypoint after passing the current point (this is known as 'sequencing'), but if necessary the active waypoint can be manually adjusted.

An important piece of terminology is a leg, which is a section of route between two waypoints. Many real-world devices deal in legs primarily, since each leg corresponds to a desired track, a distance and possibly an altitude to climb / descend. In the FlightGear route manager, the active leg is from the previous waypoint to the current waypoint - i.e the current waypoint is where you're heading to at the moment.

Defining a Route

The simplest way to define a route is to add waypoints one at a time by identifier. Since navaid identifiers are not unique, the route-manager uses your departure airport or the previously defined waypoint to 'locate' the identifier search. In practice, navaids with conflicting names are located far enough apart that this works automatically in practice.

Until departure and arrival procedures are supported, you can often define them yourself, by creating offset waypoints. The syntax is ident/radial/distance, for example TLA/347/13 defines a waypoint (which will be named 'TLA13') which is 13nm away from the TLA VOR on magnetic radial 347.

Routes can be loaded (and soon, saved) to a simple XML format, so you may prefer to create the routes in a text editor, and load them instead of entering them by hand. Support for flight-planning tools is also planned, contact the developer list if you are interested on working on such a feature.

In the future, auto-routing using airways or VOR-VOR routing will also be added.

Activating a Route

Activating a route performs certain checks, and creates start and end waypoints based on the selected departure and arrival info. For the moment, that consists of adding the departure runway as waypoint zero, but in the future (when departure procedures are supported) this will create the appropriate procedure waypoints.

This will also be the hook point for calculating cruise information, such as top-of-climb and top-of-descent points in the future.

Other devices (especially a GPS/FMS) may trigger other changes based on activating a route, such as sequencing the first leg of the route, resetting internal counters / timers, and so on.

Flying a Route

When a route is activated, the GPS system enters 'leg' mode, and will automatically sequence waypoints as they are overflow. Note that all aircraft can use the default route-manager and GPS functions, even aircraft that would never (historically) has such systems. This is a convenience to casual users, testing, and so on.

In particular, the GPS drives some properties of the generic autopilot, so 'true heading hold' mode can be used to fly the route manager route (or any other GPS course).

In aircraft with realistic navigation systems, or customised autopilots, the default behaviours above may not work; hopefully the aircraft author has provided alternative methods, such as panel instruments, to control things.

Finding an Airport

Route Manager is so simple to use that a player can simply input an airport code (e.g. KSFO) and select "true heading" under the autopilot heading control, and end up at the airport. Doing so will NOT line the pilot up with the runway, and will simply fly the plane over the airport. However, every waypoint name is unique; a player could be on the other side of the world, 5,000 miles away, and Route Manager would still lock onto the desired airport.

Lining up with Runways

Those who wish to end up lined with the runway must considerably more work. They must find out a waypoint that is directly in front of a runway, and then find out the runway's localizer. Since a localizer will not extend more than 20 miles, it is imperative to reach the waypoint first. When the player inputs the localizer frequency into their NAV1, it will direct them to the runway. For example, a waypoint near and in front of 28R of KSFO is AXMUL (see the chart HERE[1]). On the chart, it appears as "AXMUL INT", which stands for AXMUL intercept. A player is "intercepting" the runway course when they reach AXMUL. When a player reached AXMUL via Route Manager, they would follow the NAV1 Localizer. In this case, 28R's frequency is 111.7, as seen on the chart above. AXMUL is not far enough from 28R to keep turning. It's the closest waypoint to 28R, so you may want to use the waypoint before it. In this case, one of the waypoints before AXMUL is CEDES INT, or CEDES. A player can input CEDES into Route Manager, and then AXMUL, so they would reach AXMUL from CEDES. The course from CEDES to AXMUL, as seen on the chart, is straight to the runway, so a player would reach AXMUL lined up well. In essence, a player can follow route manager until within range of navaids- first the general airport frequency (KSFO, its 115.8), and then the localizer. Remember, the most effective waypoints are those that are on course for the runway. Any code with a triangle next to it or that says "INT", or is attached to an approach course is probably a waypoint- basically, any mispelled name, like NATHN, WAKER, etc. and in all caps. Check your waypoints before you fly, though! Go to mpmap01.flightgear.org, click on the nav section, and input the waypoint you want to check

You can use airnav.com to find charts- input the airport code into airports, then scroll down to the bottom to ILS approaches, and click on the runway you want. I know a lot of people want to go to KLAX, so I've saved you the trouble of getting the chart: [2] So the waypoints in this case could be anything on the chart. The 3 ones I use are: (input these into route manager, in order):

WAKER,
NATHN,
KOYEV

and then follow the localizer, 108.5

Properties

When a route is active, the route-manage provides various pieces of information based upon current aircraft position / speed, and the route progress. These values would be calculated by the navigation computer in a real system, but are handled by route-manage in FG for convenience. Values logged include the takeoff time, estimated time enroute (ETE), distance remaining enroute, and so on - browse the property tree to see what's available.