1 The idea
A camera solve assumes the whole world is still. Tracks on something that moves on its own, like the drone, disagree with every other track and pull the camera off. Mask such things out, then solve their motion separately as an object track.
Switch Solve setup from Camera solve, all tracks, to Camera solve, drone masked, to Camera + object solve. Watch the camera’s average error, the ground cone’s worst slide and the beacon’s worst slide off the drone together.
2 Hands-on
Task: get both the ground cone and the drone beacon to 1 px of slide or less.
The cone sits in the world, seen through the solved camera; the beacon rides on the drone. Ask which set of tracks each one gets its motion from.
3 Deep dive
Why a camera solve needs a still world
The solver looks for one camera that explains every track at once, treating every point as fixed in the world. A point that moves on its own fits no camera, so the solver compromises and bends the camera a little towards it.
The result is ground CG that slides even though the ground tracks themselves are fine. The average error alone won’t tell you; watch ground CG in motion.
Before you press solve, list what moves on its own in frame: people, cars, dust, shadows, the drone.
Mask moving things out of the camera solve
Draw a Roto around everything that moves on its own, for the whole shot, and feed it to the CameraTracker mask. Grow the matte a little so features don’t settle right on the object’s edge.
Small movers in the background matter too: background tracks that latch onto passing people read as jitter.
- 1Find the movers
- 2Roto for the whole shot
- 3Grow the matte
- 4Into the CameraTracker mask
- 5Solve, check ground CG
Object track: solving the object apart from the camera
Once the camera is solved from the still points, an object track uses only the tracks on the object to find how it moves and turns relative to that camera. Dedicated matchmove software can solve the camera and a moving object together.
Object tracks must sit on rigid parts that move as one, like the drone’s body, not the rotors that spin separately. They also need to be enough and spread across the object; too few and the solve won’t hold.
| CG | Attach to | Tracks used |
|---|---|---|
| Cone on the ground | World + solved Camera | Ground and rocks (still) |
| Beacon on the drone | The drone’s transform | Drone body only |
Check an object solve by stabilising it
Inverting the object’s world matrix holds the object still at the origin: the 3D version of stabilise vs match-move from TR2. If the solve is good, the object barely moves in that view.
Then watch both sets of CG in motion, through the whole shot: ground CG stays on the ground, object CG stays on the object.
A low error doesn’t mean no slide. Your eyes on the moving picture have the last word.
4 In real work
In Nuke
- Roto around the drone and everything else that moves on its own, for the whole shot, with the matte grown slightly.
- Plug the Roto into the CameraTracker (NukeX) mask input, set Mask to Mask Alpha, then track and solve.
- Export the Camera and keep ground CG, such as the cone, in world space seen through that Camera.
- Bring the drone’s solve in as an animated Axis (for example from matchmove software that solves objects).
- Parent the beacon to that Axis, not to the Camera or the world.
Common mistakes → the fix
- ✗ Leaving people, cars or the drone in the camera solve✓ Roto every mover out before solving, for the whole shot.
- ✗ Parenting CG for a moving object to the camera or the world✓ Parent it to that object’s solved transform.
- ✗ Solving an object with too few points, or with points on the rotors✓ Use points on rigid parts only, enough of them, spread across the object.
- ✗ Trusting the camera’s average error without looking at CG✓ Watch ground and object CG in motion through the whole shot.
Before you send the shot
- Every mover is masked out of the camera solve for the whole shot.
- Ground CG holds near and far, centre and edges.
- Object CG is parented to the object’s transform.
- The object solve uses rigid points only: no rotors or separately moving parts.
- Every frame has been stepped through, not just the average.
5 Check yourself
With every track in one camera solve, why does the ground cone slide?
🔒 Answer the question above and this card opens
1. What should the beacon on the drone be parented to?
2. Which tracks belong in the drone’s object solve?
Where the numbers come from: A 48-frame handheld shot (640×360) rendered in Blender (Cycles) through our desert set, with a green screen on a pole and a drone flying across. Frame 1 is the still plate’s camera. Every true position comes from the scene’s own 3D (truth.json, dist.f32). Teaching solves as in TR6: the camera from the static tracks, the drone’s pose (6 numbers per frame) from the drone tracks with the solved camera, all by least squares in your browser on our own scene’s true 2D positions plus seeded noise. Not Nuke’s or any matchmove program’s solver.