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FlightGear Flight Simulator

• A.R. Perry
  • alex.perry@ieee.org
  • Presenter and Developer

Presented at

• C. Olson
  • 
  • Project Leader

(page 1)

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About the presenter

• Alexander Perry, a FlightGear developer:
  • Single engine pilot (commercial and instrument rated)
  • Advanced and instrument ground instructor
  • Aviation safety counselor (San Diego/Imperial counties, California)

(page 2)

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The FlightGear project

• Project goals:
  • Do things `right'
  • Minimize short cuts
  • Learn and advance knowledge
  • Build better toys to play with on ordinary computers
• Inspired by David Murr, April 1996
  • Open source GPL - Free as in speech and as in beer
  • Curt Olson made a multiplatform, OpenGL based release in July 1997
• Now more than just flight aerodynamics
  • Improving graphics, clouds, and fog, time of day
  • Shaded sky with sun, moon, stars, and planets correctly drawn
  • Automated world scenery generation tools based on real world data
  • Electronic navigation systems
  • Airports and runways
  • Head up display and instrument panel
  • Photo-realistic scenery
  • Open, flexible, extensible architecture

(page 3)

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Many simulation applications

• FlightGear is used in many different ways

(page 4)

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This talk is only about visual scenery

• Among the dozens of simulator uses
  • Each has a different emphasis and technical needs
  • Unneeded features may be omitted to save resources
  • Compromises are usually made in the implementation
  • We prefer to offer run- and compile-time choices
  • One of the benefits of being an open source project

• Visual scenery is a huge resource hog
  • Application-specific optimization is critical
  • This talk reviews why scenery is necessary
  • Summarizes the standard FlightGear scenery
  • Discusses some of the easy customizations

• What is the simplest visual display we need ?

(page 5)

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Cessna 172 in the clouds







(page 6)

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Scenery is often unnecessary

• For instrument flight rules (IFR)
  • The pilots act the same inside as outside the clouds
  • They operate the aircraft by reference to the instruments
  • They navigate using electronic aids and radio instructions
• For dead reckoning trips
  • The pilots use time/heading/distance to navigate
  • The view outside is mostly optional during cruise
  • Only a few specific landmarks are needed to check progress
• For night flight
  • The world is black (except for towns and airports)
  • Need to only show a blob of light for each town

• For these cases, should we bother ?
  • Would it really just be eye candy ?

(page 7)

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Visuals can be a distraction

• Popping in and out of sunny clouds
  • Dim grey featureless background when inside a cloud
  • Blinding white glare when emerging into sunlight
  • Makes the instruments very hard to read
• Occasional small patches of ground
  • Not big enough to identify any specific landmarks
  • Not long enough to match patterns to the charts
  • Distracts pilot from flying the plane
  • Encourages erroneous changes in route
• Mountains in the distance
  • A pretty background, static and easy to draw
  • Too far away to estimate the aircraft's position
  • Appears to confirm the pilot's opinions

• So, yes, even IFR benefits from scenery
  • It all makes flying harder and more realistic

(page 8)

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On short final to land



(page 9)

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Basic scenery is also necessary

• To provide an airport area for takeoff and landing
  • For IFR flights that disappear into a cloud
  • When it isn't a conventional runway

• To show the specific landmarks and town outlines
  • For dead reckoning, pilotage, and similar
  • Doesn't take much; the occasional tower, lake, etc.

• To decide what should be seen between the clouds
  • Where the mountains are in the distance
  • And whether the plane will shortly hit one

• FlightGear has supported all that for years ...

(page 10)

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Cessna 172 on landing approach



(page 11)

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Software implementation

• Graphics are drawn using the OpenGL API
  • Using accelerated renderer such as Utah or XF4
  • Through GLX calls on Linux; Mesa/X11 is too slow

• The scene graph is managed by the PLIB library
  • FlightGear's loader passes file names to SimGear
  • Visibility and clouds are specified by weather model

• Separate XML-derived objects are also used
  • The Head Up Display is drawn in front of scenery
  • The Instrument Panel is drawn beneath the scenery
  • A big improvement over the C++ method a year ago

• What creates the many files that SimGear can load ?
  • All those gigabytes of synthetic scenery ...

(page 12)

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Montgomery field, San Diego California



(page 13)

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Simulating the World - TerraGear

• Open-source tools and rendering libraries
  • We collect free data for building 3D representations
  • The whole earth is usable in real time rendering
• Much freely available GIS data on the internet
  • Core data for FlightGear has to be unrestricted
  • Many sources of raw data cannot be incorporated
• Four categories of data are in use
  • Digital Elevation Model (DEM), 1 km grid worldwide
  • Polygon outlines for coasts, lakes, islands, and towns
  • Land use / land cover `raster' data
  • Landmarks such as lighthouses, radio and water towers

• Individual users and groups can rebuild it
  • Generate larger, slower files for faster computers
  • Use locally available, restricted, data sources
  • Optimize scenery quality for a specific application

(page 14)

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TerraGear - Screen dump




(page 15)

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TerraGear - Storage size

• It's clearly a synthetic image
  • But sufficient to understand and interpret
  • Allows cross-country navigation by pilotage
  • Where the pilot is comparing the view to a chart
• It's compact, about one kilobyte per square kilometer
  • Necessary, since about 10000 sq km may be in view

• A four level hierarchy with 10-100 ratios ...

• These tiles are demand loaded and unloaded
  • So it runs slower when the visibility is higher
  • Needs more memory to store the additional tiles too

(page 16)

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National data limitations

• Poor worldwide elevation data is already being used
• Good data is often country specific
  • Need special code to read and process file format
  • A lot of effort to do this for every country
  • Rapidly reaches the point of diminishing returns
• Many organizations collect and transform the data
  • Creating a standardized format, for their customers
  • There is a huge amount of effort involved
  • So their prices are extremely high to fund it
  • They cannot give the data away for us to use
• Maybe those organization will sell scenery
  • Run their data through TerraGear and burn some CDs
  • You can expect a high price tag for such reliable data

(page 17)

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Mismatch of scenery and charts

• Public domain data is generally of reduced quality
  • Or out of date, or selective, or local coverage, etc.
• The scenery generated from that data may be incorrect
  • Compared to the real world out there
  • But generally only in visually unobtrusive ways

• These errors are more visible in electronic navigation
  • Such as needed for instrument flight (IFR)
  • Since the route tolerances are extremely tight
• Navigating the simulated aircraft around
  • With current Jeppesen (or NOS, etc) charts
  • Can be extremely frustrating, or impossible
  • When a piece of scenery is incorrectly in the way

(page 18)

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Synthetic chart - example



(page 19)

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Synthetic charts - Atlas project

• Automatic translation of TerraGear files
  • Generates usable aviation style charts
• These charts are inaccurate to the real world
  • Therefore useless for flight in an aircraft
• Extremely accurate for the simulated world
  • When operating the FlightGear aircraft
  • Often easier to make and use printouts

• The Atlas application is for browsing
  • Can connect directly to FlightGear
  • Displays aircraft current location on moving map
  • Best used selectively by the simulator pilot
  • Most small aircraft do not contain such GPS units
  • ... with integrated moving map displays ... yet

• Invaluable to the flight instructor

(page 20)

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Colorized satellite overlay for Ramona



(page 21)

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Context cues around airport

• That insert was a quick few hours work
  • It shows the taxiway and buildings around the runway
  • The runway is no different, does it really help ?

• The default textures are intentionally fairly featureless
  • Pilots tend to fly low, similar to black hole effect
  • The other stuff helps to provide a sense of scale
  • The simulator was located at the red blob
  • This helps users to interpret the landscape

• Are these additional cues sufficient ?

(page 22)

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Short final at San Jose



(page 23)

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Do we want photorealism ?

• Is the TerraGear scenery sufficient ?

• Eye candy has no functional benefit
  • Looks nice, for spectacular screen dumps and demos
  • Helps sell the package to potential users
  • Doesn't help with usual usage of the simulator

• Can only be done for specific small areas
  • Storage need is many thousands of times larger
  • Unrealistically distinctive from a distance
• Sometimes, the aircraft stays in a small area
  • Balloons, acrobatics, model aircraft, hang gliders, etc
  • Landing practice, traversing mountain canyons, etc

• So, is photorealism just eye candy ?
  • Well, some applications rely on it ...

(page 24)

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Joining downwind at San Jose



(page 25)

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Practicing visual decisions

• Making an incorrect choice of a runway
  • Dragstrips can look like runways
  • Airports can appear to be another parking lot
  • Parking lot lights look like an approach
  • A large airport can hide a smaller one
  • A large taxiway might look like a small runway

• Operating in poor visual conditions
  • Trying to distinguish things in fog
  • Lightning flashes, heavy rain showers
  • Navigating below a low cloud layer

• It's easy to make a wrong decision at 150 mph
  • And worth practicing to avoid it

(page 26)

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How many runways at San Jose ?



(page 27)

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Design of airports

• Can airport design influence the amount of pilot mistakes?

• Arrangment and size of parallel runways
  • Runway 29 to the far left can easily be overlooked
    • Starts later
    • Lighter coloured surface
• Color and contrast of runways/taxiways
  • Taxiway `Y' has same color as runway 30L
    • Pilot knows there are two active runways
    • 30L is clearly a runway
    • At a glance, taxiway `Y' looks like the other runway

• Can simulators be used to study and evaluate airport design problems?
• What can be done if a problem is discovered?
• Simulator training a prerequisite for airport use?

(page 28)

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Airport navigation training

• Steering a taxiing aircraft is easy, but
  • The vehicle is ungainly, 40 ft wide
  • You cannot back up, or usually turn around
  • Small signs are mounted low to the ground
  • One junction may have six exits to choose
  • The paved surface may be 100 ft wide
  • Nothing indicates corners in the distance
  • A Cessna 172 has a much lower vantage point that a 747

• A lot of practice is needed to deal with this
  • A map doesn't always help enough

• Turn a wrong corner, you might end up on a runway
  • Can be bad if someone is trying to use it ...

• Airport service vehicles could also benefit

(page 29)

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The runway incursion problem

• Any occurrence at an airport that
  • Results in loss of separation with an aircraft
  • Taking off, landing, or intending to do so
• Runway incursions are made up of
  • Pilot deviations (eg pilot took a wrong turn),
  • Operational errors (eg controller made a mistake),
  • Vehicle or pedestrian deviations (went the wrong way), and
  • Operational deviations (facility coordination error).
• Average rate is 230 per year in the 1990's
  • Rising 72% from 1993 to 1997, and to 547 in 1999
  • Accidents in Atlanta, Detroit, Los Angeles, St. Louis, etc

• The FAA strategic goal: reduce accidents
  • Eliminate 80% of the 1996 fatal rate by 2007
  • Curt is extending FlightGear to support them

(page 30)

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Photo scenery, buildings, signage

• Replace the airport surroundings with photos
  • A directory with megabytes of photo texture data
  • Renders to be a bit fuzzy, but usable for taxiing
  • But rapidly overloads video capability in flight

• Add buildings and obstructions to vision
  • Drawn manually using the open source Pretty Poly Editor
  • Created by proprietary 3d image processing techniques and imported
  • Dropped into place using a file of airport objects
  • These mostly serve as navigation landmarks and distractions
  • The pilot can misidentify them from controller clearance

• Place the little signs in appropriate places
  • Their textures are computer generated on the fly
  • Locations are measured from airport engineering maps

(page 31)

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San Jose California



(page 32)

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Immersion and field of view

• Humans can see 90 degrees on each side
  • And a large angle of up and down too
  • Without moving your head, even

• Light aircraft have wrap-around windows
  • The brain processes that whole field of view
  • If view is partly missing, system is not immersive
  • Unrealistic, especially for visual navigation tasks

• A single monitor display is a poor substitute
  • FlightGear permits unlimited number of display channels
  • Each channel is a separate process on a network socket
  • Permits efficient SMP and clustering implementations
  • Limited by your number of video cards, monitors, etc

(page 33)

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Testing triple display hardware



(page 34)

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What's in the future?

• There's a lot out there ... some examples:

• FDMs are not (yet) accurate enough
  • Only suitable for conservative flights
  • Don't reflect the challenges of acrobatic maneuvering

• New consumer technologies for immersion
  • Surround projectors, head mounted displays
  • Directional sound and cockpit motion effects
  • Users will fly safe, forgetting they're not in danger

• Recent radar and visual satellite surveys
  • Enough detail to be used as photorealistic scenery
  • First, we must manipulate terabytes in real time
  • Data volume is about a million times larger than now

(page 35)

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Conclusions

• FlightGear is a simple Open Source project
  • Builds on many other projects

• Due to the subject it addresses
  • It has many issues and unusual concerns
  • Most rarely inconvenience other projects

• These elements are providing the exciting challenges
  • And variety of associated activities enjoyed by the developers

• Thank you for your interest

(page 36)

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