Real-time virtual reality technology (class notes 5)

Input device of virtual reality system

The input device is used to input the user's actions so that the user can control a virtual scene. When interacting with the virtual scene, a large number of sensors are used to manage the user's behavior, and the state of the objects in the scene is fed back to the user.
In order to realize the interaction between human and computer, it is necessary to use a special interface to input user commands to the computer, and at the same time provide feedback information in the simulation process to the user. According to different functions and purposes, there are currently many kinds of virtual reality interfaces for realizing the interaction of different sensory channels.

Tracking equipment

The function of the tracking and positioning device is to obtain the dynamic position and direction information of people in time and accurately, and send the position and direction information to the computer control system for realizing virtual reality.

Way of working:

1. The signal is transmitted by a fixed transmitter
2. The signal will be intercepted by a sensor attached to the user's head or body
3. After receiving these signals, the sensor decodes them and sends them to computer components for processing
4. Finally determine the relative position and orientation between the transmitter and the receiver
5. The data is finally transferred to the 3D graphics environment processing system
6. Then it is recognized by the system and sends the corresponding execution command

1. Related performance parameters

• Accuracy and resolution
• Corresponding time
• Robustness
• Integration
• Multilateralism
• Gregariousness
• Some other performance indicators

Electromagnetic wave tracker

It is a common non-contact space tracker locator, consisting of a control part, several transmitters and several receivers.

working principle:

• The transmitter generates a low-frequency spatially stable electromagnetic field
• Tracking subject wears several receivers to move in the electromagnetic field
• The receiver cuts the magnetic induction line to complete the conversion from analog signal to electrical signal
• Then pass it to the processor
• The processor calculates the spatial orientation of each receiver based on the received signal

advantage:

• The sensitive part depends on the tracking position and is not restricted by the line of sight
• small volume
• cheap price
• Robust

Disadvantages:

• Long delay, easily affected by metal objects or other magnetic fields, causing signal distortion
• Tracking accuracy is reduced, it can only be used for a small range of tracking work

Ultrasonic tracker

Is a non-contact position measuring device

working principle:

• High-frequency ultrasonic pulse (frequency above 20kHz) is emitted by the transmitter
• The receiver calculates the time difference, phase difference or sound pressure difference of the received signal to determine the distance and azimuth of the tracking object

Transmitter: composed of three speakers, mounted on a fixed tripod
Receiver: composed of three microphones, mounted on a small tripod
Tripod: can be placed on the helmet display, the receiving microphone can also be installed on a three -dimensional mouse Stereo eyes and other input devices

advantage:

• Not affected by ring mirror magnetic field and ferromagnetic objects
• No electromagnetic radiation
• cheap price

Disadvantages:

• Slow update rate
• The propagation of ultrasonic signals in the air decays quickly, which affects the working range of the tracker
• No block is required between the transmitter and receiver
• Background noise and other ultrasound sources can also interfere with the tracker's signal

Optical tracker

It is a non-contact position measuring device that uses optical perception to determine the real-time position and orientation of an object. The optical tracker mainly includes a photosensitive device (receiver), a light source (transmitter), and a controller for signal processing.
Working principle: Based on triangulation

advantage:

• high speed
• With higher update rate and lower delay, suitable for occasions with high real-time requirements

Disadvantages:

• Can't block sight
• It works well in a small area, and as the distance increases, the performance will gradually deteriorate

Other types of trackers

Inertial tracker

The position information is obtained through the internal calculation of the motion system, without involving the external environment

Human-computer interaction equipment

1. 3D mouse
2. Data gloves
3. Data suit
4. 3D camera
5. 3D scanner