Multi-Target Tracking

WebAR Image Tracker can track several images simultaneously - each printed target gets its own content, and each is stabilised by the same proven pose pipeline as a single target.

How it works

You compile multiple source images into one marker file. Each image is assigned a Target Index (0, 1, 2, …) in the order it was added. In the scene, you place one WebARImageTracker per index, each anchoring its own content. When the camera sees a target, that tracker's content appears; when multiple targets are visible, multiple content sets appear at once.

Setup

1. Compile a multi-image marker

In Tools ▸ WebAR Image Tracker for Unity ▸ Create Marker, drop all the source images you want to track. They compile into a single WebARImageTarget with one index per image, in the order you added them. See Creating Markers.

2. Raise Max Targets on the WebAR Controller

Select the WebAR Controller GameObject and, on its WebARTrackedRoot component, set Max Targets to the number of targets you want tracked at once (for example, 4). This tells the underlying tracker to match more than one image per frame.

3. Add one image tracker per index

Click Add Image Tracker on the WebAR Controller's Inspector once per target, then configure each:

• The first (primary) tracker holds the compiled marker in its Target File slot, with Target Index 0.
• Each additional tracker sets its Target Index to 1, 2, … matching the compile order (a named dropdown when the marker carries names), and leaves Target File blank (they share the primary's marker).
• Set each target's printed Width and Height (in centimetres) on the marker asset, per index - so a business card and a poster in the same marker each render at their own scale. (Sizes live on the asset, not the tracker.)

4. Parent content under each tracker

Put each target's content under its own WebARImageTracker GameObject. Each tracker activates its own children when its target is visible and hides them when it isn't - independently of the others.

One shared content instance on any of several markers

Sometimes you want the opposite of simultaneous tracking: several different printed images that each bring up the same content, one at a time. A product that ships in three box designs, or one exhibit label printed in three languages.

Leave Max Targets at 1 and put one WebARImageTracker per Target Index on the same GameObject, with your content parented under that GameObject. Every target in the marker stays valid at Max Targets = 1, so pointing at any one of them activates its tracker and shows the shared content. The tracker holds whichever target it locked onto until that target leaves the view, then re-acquires, so exactly one is ever active.

This costs no extra matcher work, because the tracker is still matching a single image per frame.

Performance

Tracking more than one target at a time adds matcher work per frame, which lowers the tracker rate for every target. Set Max Targets to the smallest number the experience needs. The live rate is visible as upd (Hz) on the diagnostics overlay and via WebARBridge.Instance.TrackerRateHz; per-device rates are in Browser & Device Support.

Tips

• Keep targets visually distinct. Two similar images raise the chance of a mismatch. Distinct artwork per target tracks more reliably.
• Order is the contract. Target indices follow the order images were added in the compiler. If you recompile with images in a different order, update the Target Index on each tracker to match.
• Set realistic physical sizes per target. Printed sizes live on the marker asset, one per target index, so a business card and a poster compiled into the same marker each render their content at the right scale.