Edge Tracking

Edge tracking matches the geometric contours of a 3D model against edges found in the camera image. It uses both the object's outer boundary and internal surface edges (creases, sharp features) for robust tracking.

When to Use

Works well for:

• Large machinery, engines, and equipment with lots of internal geometric detail
• Objects with sharp edges, creases, and well-defined geometry
• Partial views of large objects — internal edges remain visible even when the outline isn't fully in frame
• Scenes with cluttered or textured backgrounds — edges are more discriminative than silhouettes
• Low-contrast environments — works with weaker visual contrast than silhouette tracking
• CAD models — the edge structure matches reality closely

Struggles with:

• Smooth, featureless objects (spheres, smooth organic shapes)
• Objects where real edges don't match the 3D model (deformable objects, loose cables)
• Very small objects with few detectable edges
• Fast camera or object movement — more sensitive to motion than silhouette

Configuration

On the TrackedBody component:

• Tracking Method — Select Edge to enable

Edge tracking works directly from the mesh geometry — no tracking model generation required. Just assign the mesh and start tracking. The default parameters work well for most cases.

The Edge Tracking section of the inspector holds the tuning parameters. The keyframe translation threshold, which is the camera spacing between two live models, is 0.03 m by default, and some objects hold better with a narrower spacing, for example 0.01 m. The Reset Edge Settings to Defaults button, which is also in the context menu of the component, puts every edge setting of the body back to these defaults. It can be undone, it works on instances of a prefab, and it leaves the silhouette, score and confirm settings as they are.

The Depth Edge Threshold is the depth step in meters between neighboring pixels of the rendered depth that makes a depth edge, and it accepts values from 0.001 up to 0.5 (0.01 by default). A large object seen from far away needs a few centimeters, because curved surfaces such as cylinders then produce edges that the image does not show. A smaller value finds more subtle depth changes, and a larger value keeps only sharp ones.

The tracker reads the edge settings when a body registers, and the console states them in one line (for example "registered with depth edge threshold 0.1 m"). While the scene plays, a new Depth Edge Threshold, Search Radius, Min Gradient, Sample Step or Enable Crease Edges value reaches the tracker at its next step, and the Edge Tracking section shows the values the tracker holds. Every other edge setting takes effect when the body registers again, which is after you disable and enable the component or play the scene again.

Edge vs. Silhouette

Aspect	Silhouette	Edge
What it tracks	Object outline vs. background	Surface edges + outline
Setup	Requires pre-generated tracking model	Works directly from mesh — no model generation
Background sensitivity	High — needs contrast	Low — works in cluttered scenes
Object requirements	Visible outline	Geometric features (edges, creases)
Motion tolerance	Very resilient	More sensitive to fast motion
Best for	General objects, fast motion	Large machinery, partial views, low contrast

Quality Metrics

The quality of an edge body depends on whether AR pose fusion is in play:

• Without AR pose fusion — The quality is the share of sites that find a matching edge, divided by 0.70 and clipped to 1. A quality of 1 means that 70 percent of the sites agree. It drops when edges leave the frame or become occluded.
• Under AR pose fusion — TrackingQuality is the registration margin, which measures how closely the matched edges align with the model. It is mapped to 0 to 1, which makes the number read like the one without pose fusion, and the inspector calls it the Hold Confidence. The start of the body reads the coverage score, which the inspector calls the Start Score.

Compare the quality with the bars of the body (QualityToStartTracking and QualityToStopTracking) and never with a fixed number. See Quality Metrics for the defaults.

Tips

• Model accuracy is critical — edge tracking matches the model's geometric edges against the real object. If the 3D model doesn't closely match the real object's shape, tracking will struggle. CAD models work best because their edge structure matches the manufactured part precisely.
• For objects with both smooth areas and sharp edges, consider combining edge + depth modalities
• Smooth, curved objects with no sharp edges (spheres, organic shapes) are better suited for Silhouette Tracking — edge tracking has nothing to match on featureless surfaces