TAU / ENGINEERING GUIDE
Optical mocap markers:
sizes, mounts and compatibility.
Choose a retroreflective marker for the task and validate a replacement before ordering. Includes a size table, compatibility checklist and parameter-based selector.
Select a marker by task, working distance, mount and the requirements of the specific system. Small spheres generally suit the face, fingers and small objects; larger ones are commonly used for body and props. A similar diameter alone does not prove compatibility: coating, spectrum, shape, base and recognition stability must be checked in an actual recording.
How it works
A passive marker returns light to the camera.
Camera IR illumination lights the retroreflective sphere. Several cameras observe it from different angles and the system reconstructs its 3D position. A passive marker emits no signal of its own, unlike an active LED marker. A 3D-scanning target serves a different purpose and is not an automatic substitute.
Choosing a size
Diameter is a starting point, not the whole answer.
A larger marker is easier to see at longer distances but is less convenient for dense layouts and fine detail. A small marker supports detailed work but needs closer attention to visibility and occlusion.
| Diameter | Typical use | What to check |
|---|---|---|
| 3.0 / 4.0 / 6.4 / 9.5 mm | Face, fingers, small objects and props | Distance, layout density, attachment and occlusion |
| 14 / 19.0 / 25.4 mm | Body, objects and props | Visibility along the route, mass, base and separation of neighbouring markers |
softSoft basethreadM3 / M4 threadsnapSnap-onunknownUnknown / other
The base matters as much as the sphere.
Check fit, mass, flexibility and attachment. Soft, X-shaped and leather bases support different mounting layouts. OptiTrack M3/M4 threads and Snap-on are separate mechanical interfaces: a soft-base marker does not replace them without an adapter or a different mount.
Compatibility
Seven checks before replacement.
- Passive or active operating principle
- Illumination spectrum and camera sensitivity
- Retroreflective coating and its condition
- Diameter, sphericity and projected size
- Base, fit, mass and attachment
- Software thresholds, identification and marker layout
- A reference recording at working distances and routes
Size candidate → mechanics and optics → test recording → confirmed configuration.
TAU range
Planned TAU Lumen markers.
An in-house series is being prepared. Delivery terms and package contents are confirmed in the commercial proposal.
| Product | Description | Status |
|---|---|---|
| Marker15 | 60 × 15 mm spheres on soft bases | Series in preparation |
| Marker16X | 60 × 16 mm spheres on soft X-shaped bases | Sample and price to be agreed |
| Marker20L | 60 × 20 mm spheres on soft leather bases | Series in preparation |
Candidate selector
Check the original part.
The tool finds the closest parameter-based candidate and lists the remaining checks. It does not grant automatic compatibility.
Maintenance
Protect the coating and check the mount.
Dirt, scratches and a loose base change marker visibility. Do not rub the retroreflective surface: Vicon explicitly advises against this for the relevant markers. For TAU products, follow the cleaning procedure supplied with the specific batch.
Frequently asked questions
Replacement and selection, briefly.
Can a 15 mm marker replace a 14 mm marker?+
It is a nearest-size candidate, not a proven replacement. Check the base, recognition at working distance and behaviour in your software version.
How does a mocap marker differ from a 3D-scanning target?+
A mocap marker returns IR light to motion-capture cameras. Scanning targets help align frames and may use different materials, shapes and designs.
Can a soft-base marker replace a threaded marker?+
Only after the mounting question is resolved. Optical similarity does not remove differences in fit, mass and mechanical attachment.
Why is a marker visible nearby but lost at distance?+
Projected size, coating, viewing angle, camera settings and occlusion all matter. Compare old and new markers on the same route with unchanged settings.
Can one size be used across the whole body?+
Sometimes, but not as a universal rule. The layout depends on movement, marker density, capture volume and required detail.
What should I send for SKU verification?+
Manufacturer, system and camera model, software version, marker and base photos, diameter and working distance. Add a BOM, invoice or packaging photo if available.