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Author: Thorsten Renk

Advanced Weather

Advanced Weather is one of Flightgear’s two weather-generating systems. It operates based on a (limited) understanding of atmosphere physics – the user selects a weather situation, either from the menu or via specifying a METAR string, and the system simulates the weather from there. For instance, once the system knows how unstable the lowest layer of air is against convection, it automatically decides on the presence of thermals, turbulence, convective cloud number and visual appearance. In this way, generated weather matches cloud types in the different layers based on what would typically also occur in reality for the given weather situation.

The system renders practically all clouds in 3D. To get close to a real sky appearance, it utilizes a large variety of algorithms grouping cloudlets into layers, streaks or undulatus patterns. Combined with the ability to change the weather as a function of position, endless varieties of weather situations appear, and both in the online and offline weather modes, the sky never really looks the same.

Simply select a basic weather scenario and watch the cloud patterns change from high or low altitude!

Clouds and the terrain

Cloud layer placement in level terrain is a simple exercise, but to render weather properly in mountain areas is a challenge. The weather system continually receives information about the terrain surrounding the plane, from which the distribution of wind and turbulence close to the ground as well as the placement pattern of clouds is computed.

Try flying a mountain rescue helicopter in bad weather to see the weather system in action! Or simply go sightseeing in the mountains with a single-engine plane.

Precipitation and turbulence

Precipitation is rendered beneath overdeveloping Congestus and Cumulonimbus clouds as well as beneath layered clouds. Either via a METAR string or on the advanced options configuration tab, the outside temperature can be specified – and precipitation changes from rain into snow accordingly. Also on the configuration tab, the stability of the convective air layer can be determined. Try combining an unstable convective layer with stronger winds, and watch turbulence evolve and rugged clouds with strong vertical development appear, or select a very stable atmosphere and observe well-shaped, large Cumulus clouds evolve. Or try the thunderstorm scenario, and observe large Cumulonimbus clouds tower over the scene.

Using Environment shader effects, it is possible to add a snowline, wet terrain with gleaming puddles or drift ice into the scene – use this for best effect in rainy or snowy weather.

Try setting up a stormy scenario by adjusting the wind, and watch trees sway in the wind. Can you fly a helicopter in 30 kt winds and torrential rainfall?

Lighting

Advanced Weather is fully interfaced with the Atmospheric Light Scattering rendering framework – which means clouds in low light get differential lighting according to altitude: While cloud bottoms of Cumulonimbus clouds may already be in shadow, cloud tops can still receive light. With the sun behind them, faint clouds glow in bright radiance whereas thick clouds show shadows, making for a beautiful play of light and shade.

The weather configuration tab also contains an air pollution effect – use this to see low light colors of sky and clouds change from clean air to smog.

Try an early morning takeoff before dawn, or flying into the night, and watch the low light illuminating the scene – there’s nothing quite as nice as a sunrise in the mountains.

Advanced Weather for Flightgear – made for pilots who love to watch clouds! All features shown will be available for the next official release!

Flightgear is constantly under development, and the current development version (2.11) contains already a number of interesting features beyond what 2.10 could do – so here is some (incomplete) list of what to expect from the next release:

Novel water effects

As part of the Atmospheric Light Scattering rendering scheme, some novel features have been added to the water shader:

Subtle variations in sea color and surface reflectivity are rendered at high quality, which together with slighly patchy fog improves the visual impression significantly. In addition, an experimental effect generating surf at some coastlines is under active development (coast of Lanai, Hawaii from the EC-135 cockpit).

The environment control allows to a drift ice overlay effect to render winter scenes in cold climate (coastline near Juneau, Alaska).

Improved usability

Flightgear becomes better accessible for the novel user:

A new tooltip system has been added, identifying knobs, gauges and levers for the new user and also indicating their value, thus eliminating the need to zoom to read badly visible instruments. On-screen messages are rendered in a new gnome-like semi-transparent window style. These changes are part of a larger restructuring of the user interface, which standardizes the interaction with cockpit clickspots and adds a more intuitive view mode by right-click/drag as option.

Lighting

The Rembrandt rendering does shadows best, but this does not mean other frameworks can do nothing:

The balance of direct and indirect light has been re-adjusted to simulate the self-shading of terrain better. In clear weather, shaded surface are now rendered much darker, leading to much improved visuals in low morning or afternoon light (the B-1900D over the French Alps near Grenoble).

Air-air refueling

Fans of realistic air-air refueling will be happy:

The air to air refueling system has been much improved. It now contains a menu to select tanker type, speed and contact radius. Two new tanker planes have been added, and the contact points are now correctly specified, allowing for a much more realistic aerial refueling experience.

Ground texture resolution

Landing somewhere off an airport was never before this nice:

A high resolution shader effect has been added to the procedural terrain rendering of the Atmospheric Light Scattering framework, which renders cm-scale detail resolution. This allows for a much improved low level flight experience and more interesting helicopter operations in the terrain, as there are now visual markers available to gauge distance to the terrain (the EC-135 landing on Lanai shrubland).

Weather

The weather system has received a major upgrade. The grouping of sparse clouds into patterns is now much more realistic, replacing simple clusters by visually more interesting undulatus or wavy patterns.

As part of these changes, the rendering of low visibility scenes in Atmospheric Light Scattering has also been made more consistent.

EC-135

The next version of a well-known aircraft arrives:

The Eurocopter EC-135 is currently undergoing a major overhaul. The FDM is completely revised, leading to a more stable experience in level flight, and the cockpit is done in high-resolution photorealistic texturing (over the French Alps, close to Grenoble).

A large selection of different models is provided, all with different liveries, equipment and slightly altered FDM (over the French Alps, close to Grenoble).

Canvas

The environment becomes more interactive:

Canvas is a technology to render 2-d information into the scene – it can be used for complicated instruments or a HUD. However, it has now been extended to be applicable to scenery objects as well – this allows for novel features such as airliner docking guidance systems as shown here.

Seasonal effects

Now you don’t only have to fly in summer or winter:

As part of a restructured tree shader, deciduous trees now shed their foliage if they are above the snowline, thus they adapt to the shader-drawn snow effects better. In addition, Atmospheric Light Scattering includes now an experimental season effect (mostly tested for Europe) which allows to simulate the autumn coloring of deciduous forests and pastures.

And many improvements more…

And that’s not all:

* regional textures for Middle East, the UK, Greenland, Indonesia, the arctic sea and Madagascar have been added
* improved aircraft checklists
* better interface between Basic Weather and Atmospheric Light Scattering rendering
* tree movement in the wind
* novel animations, allowing e.g. for more realistic rendering of complex gear motion

*…

Stay tuned as we fly towards the next release!