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Aphelion

Aphelion Editor

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3 — Planar tracking and match-move

Track four corners of a flat, textured surface (a screen, a poster, a wall) and corner-pin an insert onto it so it sticks with perspective.

You will build: Video Input → Planar Tracker feeding a Corner Pin that warps an Image Input, composited over the plate with Merge.

flowchart LR
    VI[Video Input] --> PT[Planar Tracker]
    IMG[Image Input] --> CP[Corner Pin]
    PT -- 8 corner outputs --> CP
    VI --> MG[Merge]
    CP --> MG
    MG --> V[Viewer]

Before you start

  • Video Input → Viewer, file set to samples/source.mp4.
  • Pick a frame where the whole surface is visible and well lit.

Steps

1. Track the surface

  1. Add a Planar Tracker.
  2. Connect Video Input.frame → Planar Tracker.frame.
  3. Select it. Four corner handles appear in the viewport.
  4. Drag each corner onto a feature of the surface, in this order: top-left, top-right, bottom-right, bottom-left. Keep them inside the surface — the tracker matches a patch at each corner.
  5. Set the corner patches:
    • Pattern → Pattern Size (default 6) — patch size per corner, percent of width.
    • Pattern → Search Radius (default 12) — max motion per frame.
  6. Press Track ►. All four corners are solved together, sampling each source frame only once.

Each corner is an independent point tracker, so the usual point-tracking rules apply: put each corner on clearly textured detail, not on a flat or blurry area.

2. Corner-pin the insert

  1. Add an Image Input with the artwork/screen content you want to place.
  2. Add a Corner Pin.
  3. Connect Image Input.frame → Corner Pin.frame.
  4. Connect the eight corners one-to-one:
Planar Tracker.top_left_x      → Corner Pin.in_top_left_x
Planar Tracker.top_left_y      → Corner Pin.in_top_left_y
Planar Tracker.top_right_x     → Corner Pin.in_top_right_x
Planar Tracker.top_right_y     → Corner Pin.in_top_right_y
Planar Tracker.bottom_right_x  → Corner Pin.in_bottom_right_x
Planar Tracker.bottom_right_y  → Corner Pin.in_bottom_right_y
Planar Tracker.bottom_left_x   → Corner Pin.in_bottom_left_x
Planar Tracker.bottom_left_y   → Corner Pin.in_bottom_left_y

Corner values are percentages of the frame (0–100), matching the Corner Pin's own corner properties.

3. Composite

  1. Add a Merge.
  2. Connect Video Input.frame → Merge.background.
  3. Connect Corner Pin.frame → Merge.foreground.
  4. Connect Merge.frame → Viewer.frame.

Add a little Merge → Opacity if the insert should look integrated, or a Light Wrap node after the Corner Pin for a soft ambient bleed around the edges.

Match-moving the whole plate (stabilise)

To reference-stabilise instead of inserting:

  1. Add a Corner Pin on the plate itself.
  2. Wire the Planar Tracker corners into it.
  3. Turn on Border → Stabilize, which inverts the corner motion so the tracked surface is pinned in place.

Mixing the insert with the plate

Because each corner is a full tracker, you can also keyframe the corner properties by hand after a track:

  • Drag a corner in the viewport to add a manual correction at the current frame (undoable).
  • Clear removes only the tracked motion; the seed corners stay.

Troubleshooting

SymptomFix
One corner driftsIts patch is probably on low-contrast detail. Move it and re-track, or lower that corner's expectations by raising Pattern Size
Surface "breathes"The corners are too close together. Spread them to the widest usable points on the surface
Perspective flips on a fast panRaise Pattern → Search Radius
Insert is in the right place but the wrong sizeThe Image Input is fitted before pinning; set Placement → Fit and Scale on the Image Input first
"no frames could be matched"At least one corner patch has no texture. Move corners onto detailed areas