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{{Note|The HUD system will one day be replaced by a [[Canvas HUD]] system.}}


This is a short description of [[FlightGear]]s default '''Head-up display''' ('''HUD'''), it can be (de)activated with the <tt>[h]</tt>-key. To change the brightness, press <tt>[shift]</tt>+<tt>[h]</tt>.
The {{Wikipedia|Head-up display|'''Head-up display'''}} (HUD) is an important instrument in modern, mostly military, cockpits. FlightGear provides a XML-based system to relatively easily create HUDs for aircraft such as the [[F-14B]] and [[F-16]].


There are also two so called 'minimal' HUDs available which are accessible with <tt>[shift]</tt>+<tt>[i]</tt>, to return to default HUD press <tt>[i]</tt>.  
However, this article's focus is on FlightGear's default head-up displays. Those are available for any craft which does not include its own set. Have a look at [[#Further Information|Further Information]] if you're planning to create a HUD.


Some of the HUDs options can be altered in the menu: <tt>View --> Adjust HUD Properties</tt>
Activate the HUD with {{key press|h}}. Pressing it repeatedly moves through the configured colours and turns it off again. To change the brightness, press {{key press|Shift|h}}. Press {{key press|Shift|i}} to go through the available HUDs. Press {{key press|i}} to switch back to the first one at any time. Have in mind that some aircraft do assign one or more of those keys differently and therefore one or more function/s is/are missing on them.


= Features =
Some of the head-up display's options can be altered in the menu: <code>View → Adjust HUD Properties</code>


=== Aileron ===
[[File:HUD_default_overview.png|thumb|420px|Huds/default.xml]]
[[Image:HUD_aileron.jpg|thumb|200px|Aileron]]
[[File:HUD_minimal_overview.png|thumb|420px|Huds/minimal.xml]]
Monitors the bearing of the control input on the ailerons axis.
[[File:HUD_NTPS_overview.png|thumb|420px|Huds/NTPS.xml]]
:[[Aileron]]


=== Airspeed ===
== Features ==
[[Image:HUD_speed.jpg|thumb|200px|Airspeed]]
=== Control inputs ===
Current speed relating to the ambient air in knot/knots (kt/kts) (1 kt = 1.852 km/h).
; [[Aileron]]
: Monitors the bearing of the control input on the aileron's axis. Attached along the upper side is the indicator for the trim input on that axis.
: Properties: <code>/controls/flight/aileron</code> and <code>/controls/flight/aileron-trim</code>


=== Altitude ===
; [[Elevator]]
[[Image:HUD_altitude.jpg|thumb|200px|Altitude]]
: Monitors the bearing of the control input on the elevator's axis. Attached to the left the trim on this axis.
Current altitude relating to sea-level in feet (ft) (1 ft = 30.48 cm).
: Properties: <code>/controls/flight/elevator</code> and <code>/controls/flight/elevator-trim</code>


=== Autopilot ===
; [[Rudder]]
If autopilot is activ the direction of the next waypoint is displayed as well as the next two and the last waypoint of the <tt>Autopilot --> Route manager</tt> list.
: Monitors the bearing of the control input on the rudder's axis. Attached to the bottom the trim input.
:[[Autopilot]]
: Properties: <code>/controls/flight/rudder</code> and <code>/controls/flight/rudder-trim</code>


=== Elevation ===
; Throttle
Current altitude above ground in feet. Relating to the location of the aircrafts radio altimeter, therefore it's not zero if the aircraft is on the ground.
: Monitors the throttle input axis.
: Property: <code>/controls/engines/engine/throttle</code>


=== Elevator ===
=== Instruments ===
[[Image:HUD_elevator.jpg|thumb|200px|Elevator]]
; [[AMSL]] (Height <u>a</u>bove <u>m</u>ean <u>s</u>ea <u>l</u>evel)
Monitors the bearing of the control input on the elevators axis.
: Current altitude relative to sea level in feet (ft) (1 ft = 30.48 cm).
:[[Elevator]]
: Property: <code>/position/altitude-ft</code>


=== G-load ===
; g-load
Displays the g-force to the pilot in g - to avoid black-/redout.
: The {{Wikipedia|G-force}} appealing to the pilot - to avoid black-/redout.
:The value riding on top of the [[#Airspeed|Airspeed]] indicator.
: Property: <code>/accelerations/pilot/z-accel-fps_sec</code> with factor <tt>-0.03108095</tt>


=== Heading ===
; [[Avionics and Instruments#DirectionalGyro|Gyrocompass]]
[[Image:HUD_heading.jpg|thumb|200px|Heading]]
: This is an ideal version of a gyrocompass without the drawbacks of a real one. It shows heading of the aircraft relative to the geographical North Pole (true north) in degree (360 degree scale).
Direction of the aircraft relating to the geographical North pole in degree (360 degree scale).
: Property: <code>/orientation/heading-deg</code>
:[[Avionics_and_Instruments#Compass|Compass]]


=== Location ===
; [[KIAS]] ('''K'''nots '''I'''ndicated '''A'''ir'''s'''peed)
[[Image:HUD_location.jpg|thumb|200px|Location]]
: Current speed relating to the ambient air in knot/knots (kt/kts) (1 kt = 1.151 mph = 1.852 km/h).
To change the coordinates-system, go to <tt>Autopilot --> Set Lat/Lon-format</tt>.
: Property: <code>/velocities/airspeed-kt</code>


=== Pitch ===
; Latitude / Longitude
Like set with <tt>[Home]</tt>/<tt>[End]</tt>.
: Current location according to the {{Wikipedia|geographic coordinate system}}.
:It's the left marker of the [[#Elevator|Elevator]] indicator.
: To change the format of the displayed coordinates, go to <tt>Autopilot</tt> --> <tt>Set Lat/Lon-format</tt>.
: Properties: <code>/position/latitude-string</code> and <code>/position/longitude-string</code>


=== Pitch ladder ===
; Pitch ladder
Displays the aircrafts pitch relating to the grounds level/horizontal in degree. It's used as an artificial horizon.
: Displays the aircraft's pitch and roll relative to the ground's level/horizontal in degree. It's used as an artificial horizon ([[Avionics and Instruments#Attitude Indicator|Attitude indicator]]).
:The big ladder like looking indicator at the HUDs centre.
: Properties: <code>/orientation/roll-deg</code> and <code>/orientation/pitch-deg</code>
:[[Avionics_and_Instruments#Attitude_Indicator|Attitude indicator]]


=== Rudder ===
; Radio altimeter
[[Image:HUD_rudder.jpg|thumb|200px|Rudder]]
: Shows current altitude [[above ground level]] (AGL) in feet. Relating to the location of the aircraft's radio altimeter, it's not zero if the aircraft is on the ground.
Monitors the bearing of the control input on the rudders axis.
: Property: <code>/position/altitude-agl-ft</code>
:[[Rudder]]


=== Thrust ===
; Turn-bank-indicator
[[Image:HUD_thrust.jpg|thumb|200px|Thrust]]
: [[Avionics and Instruments#Turn Coordinator|Turn Coordinator]]
Monitors the thrust on airplanes or the collective of helicopters.
: Properties: <code>/orientation/roll-deg</code> and <code>/orientation/side-slip-deg</code>


=== Turn-bank-indicator ===
:[[Avionics_and_Instruments#Turn_Coordinator|Turn Coordinator]]


[[Image:HUD_default_autopilot.jpg|thumb|200px|HUD autopilot]]
[[File:HUD_default_autopilot.jpg|thumb|420px|HUD autopilot]]
[[Image:HUD_default_overview.png|thumb|200px|HUD overview]]
=== [[Autopilot]] ===
If the autopilot is active the HUD displays its settings. For each active function (heading, altitude and speed) a box will appear below the gyrocompass containing information on its mode and, if existent, the associated value.
; Heading control
: Whether it is active or not and on which mode it operates is determined by the content of the  <code>/autopilot/locks/heading</code> property.
: The values are taken from <code>/autopilot/settings/heading-bug-deg</code> and <code>/autopilot/settings/true-heading-deg</code>.


; Altitude control
: Active mode: <code>/autopilot/locks/altitude</code>
: Their values: <code>/autopilot/settings/target-altitude-ft</code>, <code>/autopilot/settings/vertical-speed-fpm</code> and <code>/autopilot/settings/target-agl-ft</code>.


= Further Information =
; Speed control
: Active mode: <code>/autopilot/locks/speed</code>
: Their values: <code>/autopilot/settings/target-speed-kt</code> and <code>/autopilot/settings/target-speed-mach</code>


The basic setup of the above described default HUD is defined at
:<tt>$FG_ROOT/Huds/Default/default.xml</tt>
There is also a 'Runway projection' available which is, because of some issues, disabled by default.


Documentation can be found at
[[File:HUD_default_gps.jpg|thumb|420px|HUD GPS]]
:<tt>$FG_ROOT/Docs/README.xmlhud</tt>
=== [[GPS]] ===
The upper left hand corner shows the most important information on the actual state of the GPS. Namely these are (line by line):
: the mode the GPS operates in and the active waypoint's identifier.
: the distance "D" (in nautical miles, nm) and the calculated time to this waypoint "TTW".
: the bearing "BRG" to the active waypoint and the course deviation "XTR" based on the leg from the previous waypoint.
: the current speed relative to the ground "GS".


Since FlightGear 0.9.10 there is ''also'' a newer and more flexibly HUD-system available. An example can be found at
:<tt>$FG_ROOT/Huds/NTPS.xml</tt> and documentation at
:<tt>$FG_ROOT/Docs/README.hud</tt>.
Also have a look at <tt>$FG_ROOT/Huds/README</tt>.


== preferences.xml ==
=== Big fat arrow ===
While the instruments and their behaviour are set in the Huds-directory, the basic settings and the look regarding to any HUD are set in <tt>$FG_ROOT/preferences.xml</tt>. Search the file for <tt><hud></tt> and you will find a list of properties. For a short description of those have a look at [[#Property_tree|property tree]]. But I'll give some of them a closer look:
Remains of a going to be useful instrument.
: To get rid of it, remove or comment "runway.xml" from/in <tt>$FG_ROOT/Huds/[http://mapserver.flightgear.org/git/?p=fgdata;a=blob_plain;f=Huds/default.xml;hb=HEAD default.xml]</tt>.
: To make it point to the airport selected by menu item "Tower Position", apply patches as shown [http://sourceforge.net/mailarchive/message.php?msg_id=30422572 here].


=== Colour ===
The prefered thing one would like to customize is, I guess, the HUDs colour.


Discover your own settings is quite easy: Access the property tree via the Menu  <tt>File --> Browse Internal Properties</tt> (<tt>[/]</tt>-character) '''or''' via the [[Property_Tree#Property_server|Property server]] and your browser. Go to sim/hud/color, e.g. http://localhost:5500/sim/hud/color, edit a value and watch the result in FlightGears window instantly.
== Further Information ==
HUDs may be replaced or added by changing or adding their paths in <tt>preferences.xml</tt> or by setting the paths as command line options. To change the order of the existing ones the options would be: <code>--prop:/sim/hud/path[1]=Huds/minimal.xml</code> <code>--prop:/sim/hud/path[2]=Huds/default.xml</code>


Once the decision is made head back to preferences.xml, copy the <color n="0">-tag and paste it on top of the colours within the <palette>-tag. Rename the existing tags in numeric order and finally put your discovered values in the  new one. It should look like this, except your own values, of course:
If you consider to create your own HUD have a look at [[Canvas HUD]] first.
    <current-color type="int">0</current-color>
    <palette>
    <color n="0">
      <transparent type="bool">true</transparent>
      <antialiased type="bool">false</antialiased>
      <brightness type="float">1</brightness>
      <alpha type="float">0.67</alpha>
      <red type="float">0.1</red>
      <green type="float">1.0</green>
      <blue type="float">0.3</blue>
    </color>
    <color n="1"><nowiki><!-- day --></nowiki>
      ...
    </color>
    <color n="2"><nowiki><!-- night --></nowiki>
      ...
    </color>
    </palette>


=== Font ===
The basic settings regarding to any HUD are set in <tt>$FG_ROOT/[http://mapserver.flightgear.org/git/?p=fgdata;a=blob_plain;f=preferences.xml;hb=HEAD preferences.xml]</tt>. Search the file for the <tt><hud></tt>-tag and you will find a list of properties.


    <nowiki><font></nowiki>
The setup of the default HUD is defined at <tt>[[$FG_ROOT]]/Huds/[http://mapserver.flightgear.org/git/?p=fgdata;a=blob_plain;f=Huds/default.xml;hb=HEAD default.xml]</tt> and documentation can be found at <tt>$FG_ROOT/Docs/[https://sourceforge.net/p/flightgear/fgdata/ci/next/tree/Docs/README.hud README.hud]</tt>.
    <name type="string">Helvetica.txf</name>
    <size type="float">8</size>
    <nowiki></font></nowiki>


To change font just enter another name out of the ones in $FG_ROOT/Fonts (case sensitive!). For more information about those fonts and on .txf format peruse $FG_ROOT/Fonts/README.


Since the size is type 'float' values like '7.449' are allowed, too.
== Additional HUDs ==
; Generic helicopter HUD
: This is a generic HUD for helicopters, inspired by MIL-STD 1295A and the AH-64A IHADSS symbology. [http://stefan.gofferje.net/downloads/flightgear/file/6-generic-helicopter-hud Download]


=== Path ===
; HeliHUD
/!\ Just a draft and maybe not correct.
: Designed to fly helicopters in Helicopter View it is also handy for any craft with a not yet finished cockpit. It also contains a minimalistic HUD only showing some navigational information such as compass and GPS. The [http://beggabaur.rocks/fgfs/helihud_0.3.tar.bz2 download] contains instructions and specs.


  <path>Huds/Default/default.xml</path>
; V(MX)-22 Osprey HUD
  <path>Huds/NTPS.xml</path>          <nowiki> <!-- new HUD --></nowiki>
: [http://stefan.gofferje.net/downloads/flightgear/file/1-hud-for-vmx-22-osprey Download]
The first one is the default HUD mentioned above. It is for the old HUD only.
The second is the first one of the 'minimal HUD's and it is for the new HUD only. The other 'minimal' one is called by the code (I guess), its path is Huds/Minimal/default.xml.


For each <path> are some more HUDs available, a complete list (except aircraft specific):
[[Category:FlightGear feature]]
 
[[Category:Menubar]]
old HUD:
Huds/Custom/default.xml
Huds/Default/default.xml
Huds/Engineering/default.xml
Huds/Minimal/default.xml
 
new HUD:
Huds/NTPS.xml
Huds/default.xml
 
 
== Property tree ==
More information about FlightGears property tree and on how to access it can be found at its page: [[Property_Tree|Property Tree]].
 
Paths starting with '$FG_ROOT/' apply to the file system, the others are intra-property tree.
/sim/hud
  current-color  (0|1|2...)    int    One out of /sim/hud/palette
  enable3d        (false|true)  bool    hud n=0 3D off|on
  enable3d[1]    (false|true)  bool    hud n=1 3D off|on
  frame-stat-type (tris|???)            ???
  path            (Huds/...)            Path to hud n=0
  path[1]        (Huds/...)            Path to hud n=1
  visibility      (false|true)  bool    hud n=0 hidden|visible
  visibility[1]   (false|true)  bool    hud n=1 hidden|visible
/sim/hud/color/          Contains settings of current-color
    alpha        (0...1)      float  0=invisible, 1=nontransparent
    alpha-clamp  (???)                ???
    antialiased  (false|true)  bool    Antialiasing off|on
    blue          (0...1)      float
    brightness    (0...1)      float  0=dark/black
    green        (0...1)      float
    red          (0...1)      float
    transparent  (false|true)  bool    Transparency off|on
/sim/hud/font/
    name          (*.txf)      string  One out of $FG_ROOT/Fonts
    size          (8)          float  Size of font
/sim/hud/palette/
/sim/hud/palette/color/        Settings of predefined colors, nearly
/sim/hud/palette/color[n]/      the same options as in /sim/hud/color.

Revision as of 09:40, 15 January 2018

Note  The HUD system will one day be replaced by a Canvas HUD system.

The Head-up display This is a link to a Wikipedia article (HUD) is an important instrument in modern, mostly military, cockpits. FlightGear provides a XML-based system to relatively easily create HUDs for aircraft such as the F-14B and F-16.

However, this article's focus is on FlightGear's default head-up displays. Those are available for any craft which does not include its own set. Have a look at Further Information if you're planning to create a HUD.

Activate the HUD with h. Pressing it repeatedly moves through the configured colours and turns it off again. To change the brightness, press ⇧ Shift+h. Press ⇧ Shift+i to go through the available HUDs. Press i to switch back to the first one at any time. Have in mind that some aircraft do assign one or more of those keys differently and therefore one or more function/s is/are missing on them.

Some of the head-up display's options can be altered in the menu: View → Adjust HUD Properties

Huds/default.xml
Huds/minimal.xml
Huds/NTPS.xml

Features

Control inputs

Aileron
Monitors the bearing of the control input on the aileron's axis. Attached along the upper side is the indicator for the trim input on that axis.
Properties: /controls/flight/aileron and /controls/flight/aileron-trim
Elevator
Monitors the bearing of the control input on the elevator's axis. Attached to the left the trim on this axis.
Properties: /controls/flight/elevator and /controls/flight/elevator-trim
Rudder
Monitors the bearing of the control input on the rudder's axis. Attached to the bottom the trim input.
Properties: /controls/flight/rudder and /controls/flight/rudder-trim
Throttle
Monitors the throttle input axis.
Property: /controls/engines/engine/throttle

Instruments

AMSL (Height above mean sea level)
Current altitude relative to sea level in feet (ft) (1 ft = 30.48 cm).
Property: /position/altitude-ft
g-load
The G-force This is a link to a Wikipedia article appealing to the pilot - to avoid black-/redout.
Property: /accelerations/pilot/z-accel-fps_sec with factor -0.03108095
Gyrocompass
This is an ideal version of a gyrocompass without the drawbacks of a real one. It shows heading of the aircraft relative to the geographical North Pole (true north) in degree (360 degree scale).
Property: /orientation/heading-deg
KIAS (Knots Indicated Airspeed)
Current speed relating to the ambient air in knot/knots (kt/kts) (1 kt = 1.151 mph = 1.852 km/h).
Property: /velocities/airspeed-kt
Latitude / Longitude
Current location according to the geographic coordinate system This is a link to a Wikipedia article.
To change the format of the displayed coordinates, go to Autopilot --> Set Lat/Lon-format.
Properties: /position/latitude-string and /position/longitude-string
Pitch ladder
Displays the aircraft's pitch and roll relative to the ground's level/horizontal in degree. It's used as an artificial horizon (Attitude indicator).
Properties: /orientation/roll-deg and /orientation/pitch-deg
Radio altimeter
Shows current altitude above ground level (AGL) in feet. Relating to the location of the aircraft's radio altimeter, it's not zero if the aircraft is on the ground.
Property: /position/altitude-agl-ft
Turn-bank-indicator
Turn Coordinator
Properties: /orientation/roll-deg and /orientation/side-slip-deg


HUD autopilot

Autopilot

If the autopilot is active the HUD displays its settings. For each active function (heading, altitude and speed) a box will appear below the gyrocompass containing information on its mode and, if existent, the associated value.

Heading control
Whether it is active or not and on which mode it operates is determined by the content of the /autopilot/locks/heading property.
The values are taken from /autopilot/settings/heading-bug-deg and /autopilot/settings/true-heading-deg.
Altitude control
Active mode: /autopilot/locks/altitude
Their values: /autopilot/settings/target-altitude-ft, /autopilot/settings/vertical-speed-fpm and /autopilot/settings/target-agl-ft.
Speed control
Active mode: /autopilot/locks/speed
Their values: /autopilot/settings/target-speed-kt and /autopilot/settings/target-speed-mach


HUD GPS

GPS

The upper left hand corner shows the most important information on the actual state of the GPS. Namely these are (line by line):

the mode the GPS operates in and the active waypoint's identifier.
the distance "D" (in nautical miles, nm) and the calculated time to this waypoint "TTW".
the bearing "BRG" to the active waypoint and the course deviation "XTR" based on the leg from the previous waypoint.
the current speed relative to the ground "GS".


Big fat arrow

Remains of a going to be useful instrument.

To get rid of it, remove or comment "runway.xml" from/in $FG_ROOT/Huds/default.xml.
To make it point to the airport selected by menu item "Tower Position", apply patches as shown here.


Further Information

HUDs may be replaced or added by changing or adding their paths in preferences.xml or by setting the paths as command line options. To change the order of the existing ones the options would be: --prop:/sim/hud/path[1]=Huds/minimal.xml --prop:/sim/hud/path[2]=Huds/default.xml

If you consider to create your own HUD have a look at Canvas HUD first.

The basic settings regarding to any HUD are set in $FG_ROOT/preferences.xml. Search the file for the <hud>-tag and you will find a list of properties.

The setup of the default HUD is defined at $FG_ROOT/Huds/default.xml and documentation can be found at $FG_ROOT/Docs/README.hud.


Additional HUDs

Generic helicopter HUD
This is a generic HUD for helicopters, inspired by MIL-STD 1295A and the AH-64A IHADSS symbology. Download
HeliHUD
Designed to fly helicopters in Helicopter View it is also handy for any craft with a not yet finished cockpit. It also contains a minimalistic HUD only showing some navigational information such as compass and GPS. The download contains instructions and specs.
V(MX)-22 Osprey HUD
Download
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