The horizon under the eye: which way is up, which way is north, and how fast the ground beneath is moving. Measured against the nearest body by surface distance, in render axes, and null with no body in reach.
An attitude indicator is a picture of this frame from inside the hull, and
a surface speed is the ship's velocity with groundVelocity taken out. Both
are drawn from here rather than from the world because they are questions
about the frame the eye is presented in, and the snapshot has already
settled that.
Members
bodyreadonly
The address of the body it is measured against.
eastreadonly
north × up, unit — the way the ground turns on a prograde body.
groundVelocityreadonly
The velocity of the ground under the eye from the body's spin, m/s.
northreadonly
The body's pole, flattened onto the horizon, unit.
upreadonly
Away from the body's center, unit.