Tracking
Work the airspeed, the angles, the load factor and the rates out from how an object moves.
With no flight model to write it, a flight can watch the aircraft instead. Give the provider the object that moves:
const jet = useRef<Group>(null);
<FlightProvider track={jet} seaLevelY={0}>
<group ref={jet}>
<primitive object={gltf.scene} />
</group>
</FlightProvider>;Each frame, before any other frame callback, it reads the object's world transform and works out:
- the airspeed, from how far it moved;
- the angle of attack and the sideslip, from which way it moved in its own frame;
- the load factor, from how its path curves and which way gravity pulls;
- the roll, pitch and yaw rates, from how it turned;
- the altitude, from its height above
seaLevelY, if that is given.
The rest, such as the throttle, the controls and the day, keeps whatever is written to it.
Which way it faces
The tracker needs to know which way the object flies and which way is its up. By default it flies along −Z with +Y up, as three.js' convention has it. A model built another way says so:
<FlightProvider track={jet} forward={[1, 0, 0]} up={[0, 1, 0]}>Options
| prop | default | meaning |
|---|---|---|
track | none | an Object3D, or a ref to one |
forward | [0, 0, -1] | which way the object flies, in its own frame |
up | [0, 1, 0] | which way is its up, in its own frame |
seaLevelY | none | the world height of sea level, in metres. Left out, the altitude is not tracked |
wind | none | the wind in world space, m/s: the airspeed is through the air, not over the ground |
worldUp | [0, 1, 0] | which way is up in the world, for gravity |
Options written inline are fine: they are read in the frame, and compared by value.
Smoothing
A position differenced frame to frame is noisy, and its acceleration twice so. The tracker eases them: the velocity follows in about 0.05 s, the acceleration in 0.15 s and the rates in 0.08 s. A real aircraft changes far more slowly than that, so the numbers follow it closely without a frame's jitter.
The first frame only starts watching, as does a frame more than 0.25 s after
the last one, so a tab coming back from the background does not see a jump of
several hundred metres. flight.resetTracking() starts it over by hand, after
a teleport for instance.
Held still
Tracking measures motion through the world. A model held still in a showcase, with the camera orbiting it, tracks as at rest: write the airspeed and the angles by hand instead, or move the model through the world.
Next, read it.