A pass staged the way a model shop stages one: the ship on a rail, the camera standing off it, and the framing solved rather than authored.
The alternative — and what a screen-beat pass is — puts the whole of a shot's
dynamism in the hull's offset from a camera that never moves. That
reproduces a tracked bounding box exactly and describes a ship that cannot
exist: sampled, tng-intro's cruise flew its hull along a track whose
perpendicular residual was 14% of its own length, at speeds between 0.5 and
629 m per frame, with the nose a mean 54° off the direction of travel and
157° off it at worst. Nothing is wrong with any single beat. What is wrong is
that a screen track is three numbers a hull's position has to satisfy, and
six degrees of freedom were being spent satisfying them.
Spending the camera's six instead costs nothing measurable and buys the physics outright, because the three measured channels are preserved exactly:
- the hull is on a
LinePath, so its track is straight and its speed is whatever its own throttle says, andorientationAlonggives an attitude that cannot slide off the velocity because it does not vary; - the camera stands at
ship − range · standoff, so the range channel is satisfied by construction at every frame rather than fitted; - the camera aims through
frameTarget, so the screen mark is satisfied by construction too.
What is left free is standoff — where the camera stands relative to the
hull — and that is a real staging decision rather than a fitted number: it
chooses which face of the ship the shot shows and therefore what the key
lights. A constant standoff is a camera flying formation; a turning one is a
camera the ship overtakes.
The cost is that the camera moves, so this cannot stage a shot the reference measures as locked. The reference's credits play over a starfield with 375 to 433 matched inliers at scale 1.0000 — a locked-off camera, and the one constraint in the piece that a moving camera would break. Those passes stay screen-beat passes and get their physics from a straight rail alone.
cinematic.ts:1034Members
marksreadonly
Where the hull sits in the frame and how large it reads: the measurement, unchanged, and still the thing a diff against the reference scores.
railreadonly
The hull's rail, in the shot's stage axes.
standoffreadonly
The direction from the camera to the hull, in stage axes — as orientations whose −Z is that direction, so the interpolation between knots is a slerp and cannot leave the unit sphere.
upreadonly
Roll reference for the derived pan, stage axes.