Workflows

2D/3D Constraints

Match hand-tracked points to mesh vertices to place geometry against the camera, on the scene or on a solved object.

Sometimes you already know the 3D shape of something in the shot: a building, a set piece, a vehicle, a survey model. When you do, you can pair points on that model with tracked markers and solve straight from those pairs.

It answers two different questions depending on which way you run it. Either "where was the camera?" or "where does this model go?".

The links live in the Movie Clip Editor sidebar, Dope Track tab, under 2D/3D Constraints. Keeping them there means there's never any doubt about which clip you're on. It's whichever one that editor is showing. The solving buttons are on the 2D/3D Constraints node in the node editor.

Scene Or Object

Everything you link belongs to a target, chosen from the Constrain To dropdown at the top of the panel.

Scene is the default and there's exactly one per clip. Use it for anything that doesn't move: buildings, floors, set walls.

An object is anything you add with the + button, and you can have as many as you like. Use these for geometry that rides on a solved moving object, like a model that has to sit on a moving car.

Links are scoped to their target, so the same track name can be linked under Scene and under an object and mean two completely different 3D points. Switching the dropdown switches which set you're looking at.

Hand-Tracking The Points

Both paths need tracked 2D markers on features you can also identify on your model. Corners, bolt heads, painted marks, window edges. Track them in the Movie Clip Editor the normal way.

Aim for at least six, and spread them out. Different depths, different parts of frame. Points bunched on one flat surface or in one corner give the solver almost nothing to work with, and the result will wobble.

Linking

1. Select a tracked marker in the Movie Clip Editor.
2. Put your mesh into Edit Mode in the 3D Viewport.
3. Select the vertex, edge or face center that marker sits on.
4. Press Link to Track.
5. Repeat.

Links resolve live against the mesh, so editing geometry afterwards keeps them attached to the right elements.

The list shows every link with its current error. Press X on a row to remove one, or the bin icon to clear them all.

Aligning To The Scene

With Constrain To set to Scene, the 2D/3D Constraints node gives you:

Use Line Up when the model is the thing you trust. A surveyed set, a measured building, real architectural drawings. The camera moves to fit reality.

Use Align Geometry when the camera solve is what you trust and the model needs to drop into it. This is the common one after an Auto Track: the camera is already right, you just want the proxy building sitting where the real one is.

Aligning To A Solved Object

This is how you get a model riding correctly on something that moves.

You need an object solve first, and the hand tracks you intend to link must be wired into that Object Solve node's Tracks input before you solve it. The alignment fits your mesh to the 3D points the object solve produced from those tracks, so tracks that weren't part of the solve have nothing to fit to.

1. Solve the object with your hand tracks connected to Tracks.
2. In the Clip Editor panel, press + on Constrain To and name the target to match the Object Name on the Object Solve node.
3. Link tracks to vertices exactly as before, with that target selected.
4. On the 2D/3D Constraints node, pick the object and press Align to Object.

Your mesh moves onto the solved object's motion.

The node tells you what it found before you press anything: how many constraints, across how many pieces of geometry, and which ones. If a linked track isn't in the object's solve it names it, so you know exactly which one to fix.

Reading The Error

After solving, both the panel and the node report average and worst reprojection error in pixels for the current frame. Under about 2 pixels shows a tick, above it shows a warning.

The per-link errors matter more than the average. One link far worse than the rest is almost always a mistake, usually a marker paired to the wrong vertex. Delete that one and solve again. Adding more points around a bad link doesn't fix it, it just dilutes it.

Scrub through the shot and watch the numbers. Error that's fine on one frame and terrible on another usually means the underlying track slipped somewhere.

Parented Geometry

If the mesh you're aligning is parented to something, like a reconstruction root, the alignment moves the parent rather than breaking the relationship. Your hierarchy survives.

When It Doesn't Work

Link is rejected. The selected marker and the panel have to be on the same clip. If the Clip Editor switched clips, switch back.

Nothing happens when you press Link. The mesh needs to be in Edit Mode with an element selected, and a marker needs to be selected in the Clip Editor.

"Target is not the solved object." The Constrain To name has to match the Object Name on the Object Solve node exactly.

"None of the linked tracks are in this object's solve." Those tracks weren't wired into Tracks when you solved. Connect them and re-solve.

"Links for this object exist on several clips." The same target name has links on more than one clip, usually because you tracked on the movie and linked on the extracted frames. Keep one set and clear the other.

The solve is unstable. Too few links, or all of them on one plane. Add points at different depths.