Tracking is a special technology that lays the foundation for interacting with the virtual world. This technology is used for defining the position and orientation of a real object in a virtual environment.
Three spatial coordinates (x, y, z) and three angles (α, β, λ) define the position and orientation in space. Position and orientation of a real object in space are traced using special sensors and markers. The sensors receive the signal from the moving real object and transmit the information to the computer.
Virtual reality (VR) tracking system is a kind of a copy of existing natural positioning and orientation methods. «Natural» tracking systems in the real world are human sensory organs. E.g. eyesight helps a human being find its position in relation to other objects and people.
No system can be treated as a full-fledged VR system unless it knows the position and orientation of the user and user’s actions at any moment of time. Tracking arranges submission of this information to the system «brain».
Tracking can be compared to eyes and ears of a VR system.
Optical tracking systems are based on the same philosophy as the stereoscopic vision of a human being.
When a person views something with two eyes, he or she can define the distance to an object, its orientation and its movement in three dimensions.
How does it work
Optical tracking is based on tracing special optical markers located on the VR interfacing device.
The tracking system transmits information to the computer where the information is processed. After that the system reacts to changes in position and orientation of the interactive device. When this happens, it modifies the virtual environment in accordance with the pre-set interaction scenario.
One of the tasks of the optical tracking system is calibration in the real-time coordinates. This allows establishing one-to-one link between real-time and virtual coordinates. Thus, a person in the real world can «take» an object with his or her hand or using a special device, while the system duplicates this action in the virtual environment.
EligoVision solutions based on optical tracking
- augmented reality technology based on «living 3D markers»: marker and markerless technologies (6 DOF).
- interactive augmented reality studio — AR Studio (6 DOF).
- virtual reality 3D Pointer device (5 DOF).
Downsides of standard optical tracking based on 2 or more cameras
The main drawback of optical tracking system is the need to calibrate optical receivers (cameras) precisely. Such a system would usually require 2 or more cameras. The scanning area is the crossing region of the cameras' fields of vision. Larger interface areas need more cameras, thus complicating the procedure of the cameras' intercalibration. However, optical tracking system are commonly used since they are more reliable and affordable.
Professional optical tracking systems by the leading international vendors presently use from 2 to 4 cameras in each tracking system. Systems with two or more cameras need internal calibration, i.e. setting up the relationship between the external dimensions of the mask pattern and its image in the camera sensor. After that the external calibration should be performed to link the coordinates (physical location) of cameras in relation to each other and then in relation to the virtual coordinates (as a rule, these are the coordinates of the screen serving as the «window» to virtual reality world).
The tracked point or object pertains to three-dimensional space. One projection is not enough to define its coordinates and angles. Cameras have flat sensors. Thus, two cameras are required for 3D spaces — one flat projection per each camera. That is why cameras are configured for paired operation in standard optical tracking systems.
When you know the spatial position of the cameras you can reproduce the position of the optical signal source using the epipolar geometry methods.
When 2, 3, 4 or more cameras are used, they should be calibrated in pairs. This used to be a manual work, but now it’s semi-automatic. The price of such systems starts from 10 000 USD.
One-camera professional optical tracking by EligoVision
We developed the optical tracking technology based on one camera only. This innovative and highly convenient solution allows cutting the overall cost of system installation and operation significantly.
In the professional tracking technology by EligoVision one camera reads spatial coordinates of an object and its orientation (2 angles and 3 coordinates) at the same time.
Specially for this system we developed an innovative interactive device called 3D Pointer by EligoVision.
Standard optical tracking systems use only the crossing region of both cameras’ fields of vision. In 3D Pointer system only one camera is required for this purpose. Additional cameras can also be used in our tracking systems, while their purpose would be to expand the system coverage area up to several hundred square meters. Besides, paired calibration of cameras is not required.
- easier system calibration;
- good scalability of the system;
- use of the standard FireWire (IEEE 1394) interface;
- standard lighting conditions;
- the system can be both fixed and mobile;
- the system cost is reduced at least twice (in most cases there’s a three-times reduction)!