Active and passive versions available
Active markers are infrared light emitting elements, mostly LEDs. All active markers provided by ART are just emitting radiation when the tracking cameras are sensitive, thus have to be synchronised with the cameras. Synchronization can be done by a wired connection between the tracking system and the electronics controlling the active markers, but can also be done in a wireless way: For wireless synchronization a coded IR flash is sent out by a tracking camera. The active markers’ electronics recognize the coded flash and activate the LEDs.
Passive markers are retroreflective, i.e. they reflect the incoming IR radiation into the direction of the incoming light.
Both active and passive markers will give the 3DOF (3 degrees of freedom).
In ART tracking systems different types of LED-based active markers are used, depending on the application.
All active markers provided by ART are controlled by special electronics that ensure snychronization with the tracking cameras and require a power supply.
- Simple and robust markers providing visibility up to long distances within a ca. +/- 60° angular range of visibility
- Applied to mini circuit board (dimensions: 6 x 6 mm)
- Electronics required for synchronization: AMC (see below)
- Cable length between marker and electronics max. 30 cm
- Range up to 20 m possible
Big active flat markers
- Several single LEDs per marker, covered with light scattering surface
- Allows tracking at very long distances
- Visibility angle up to 180°
- Suitable for tracking in sunlight
- Special feature: Magnetic base for easy positioning on metal surfaces
- Diameter 30 mm
AMC (Active Marker Controller) for active markers
The active target for active markers consists of the active marker controller (AMC) and the single active markers. The AMC receives an optical or wired synchronization signal from the tracking system and activates the LED markers. Up to 6 active markers can be connected to the AMC.
A power supply of 3-5 V is required.
The passive markers most commonly used in tracking systems, including ART’s, are retroreflectors (see picture below). These markers reflect incoming IR radiation back in the direction of the incoming light.
More precisely the IR radiation is back-reflected into a narrow range of angles around the source of the incoming light. These markers are mostly spheres covered with retroreflecting foils, but can also be stickers made from retroreflecting material.
Retroreflecting sheets or foils available on the market can be based on two different optical principles:
- Three mirrors, arranged in 90° angles to each other, reflect light in the described way. Mostly foils with arrangements of lots of very small mirrors in a plane are used.
- Glass balls (with appropriate refraction index) focus incoming light onto the opposite surface of the ball. A layer of microscopic glass balls, carried by a reflecting material, acts as a retro reflector. These foils can be fabricated on a flexible carrier material, thus they are widely used for equipping spherical markers with retroreflecting surfaces.
Spherical markers are plastic spheres with a centric M3 threaded insert, which are coated with a highly retro-reflective film.
They are also available as a protected version with a robust surface. We provide these robust markers in the following sizes: 14 mm and 16 mm.
Available sizes (mm/inch): 12 (0.47), 14 (0.55), 16 (0.63), 20 (0.79), 30 (1.18).
Flat markers are pre-cut circular pieces of self-adhesive retro-reflective film.
Available sizes (mm/inch): 10 (0.39), 12.5 (0.49), 15 (0.59), 20 (0.79).
Ring Markers (Cylindrical Markers)
Ring markers allow 5DOF tracking of cylindrical objects. They can be used, for example, for tracking of 3D glasses or of VR input and drawing pens, as well as for more precise detection of the working points of tools with extensions. For more information regarding these applications, simply contact us here.