Real-time virtual reality technology theory (Classroom Notes 6)

Output device of virtual reality system

When the user interacts with the virtual reality system, whether he can obtain the same or similar perception as the real world and produce the feeling of being "immersive" will directly affect the realism of the system.
In order to achieve the immersive characteristics of the virtual reality system, the output device must be able to transform various perception signals in the virtual world into multi-channel stimulus signals such as vision, hearing, touch, taste, etc. that humans can receive

1. Related concepts of visual perception

1. Field of view: The area that can be seen by the eye is called the field
   of view.

2. Perspective: visual perception on the size of the visual object measured
   perspective normal lighting conditions should not be less than 15 °, under conditions of low light viewing angle should not be less than 21 °
   viewing angle can be calculated by the following formula
   

3. Visual generation: the external scene emits or reflects light to stimulate the photoreceptor cells of the retina to make the visual nerve feel

4. Stereovision: The human eyes are separated by 58 ~ 72mm. When observing an object, there are certain differences in the positions and angles observed by the two eyes, so the image observed by each eye is different.

5. Diopter: The role of the eye in refracting light is called diopter, and the ability to express dioptric power with optical power is called diopter.

6. Pupil: How it works: The pupil is the hole in front of the lens. Its adaptation to light intensity is done automatically. Through the adjustment of the pupil, always keep an appropriate amount of light into the eye, so that the image of the object falling on the retina is clear, and there is no excessive light to burn the retina. Although the pupil is not a refractive element in the eyeball optical system, it plays an important role in the eyeball optical system. The pupil can not only respond to light and dark, adjust the light entering the eye, but also affect the depth of focus and spherical aberration of the eyeball optical system.

7. Resolution: Resolution is the ability of the human eye to distinguish between two points. When the two black spots on the space plane are close to each other to a certain degree, the observer at a certain distance from the black spots cannot distinguish them, which means that the human eye's ability to distinguish the details of the scene is limited. This limit is the resolution

8. Persistence of vision: also known as the "afterglow effect", example: ancient Chinese walking lights

Visual perception equipment

1. Helmet display
2. Boom display
3. Cave display
4. Responsive workbench display device
5. Wall projection display equipment
6. Stereo eye display system
7. Three-dimensional display

2. Hearing perception equipment

Knowledge related to auditory perception

1. Sound: It is a sound wave generated by the vibration of an object. It is a wave phenomenon that is transmitted through a medium (air or solid, liquid) and can be perceived by human or animal hearing organs. The object that initially vibrated is called the sound source. Sound vibrates in the form of waves. Sound waves can propagate through all matter (except vacuum). Its propagation speed is determined by certain physical properties of the sound transmission medium, mainly mechanical properties. For example, the speed of sound is related to the density and elastic properties of the medium, so it also changes with the state parameters such as the temperature and pressure of the medium. The speed of sound in the gas is about several hundred meters per second, which increases with increasing temperature. Generally, the speed of sound in solid media is the largest, the speed of sound in liquid media is smaller, and the speed of sound in gas media is the smallest.
2. Frequency range: The frequency range that human ear can perceive is about 20Hz ~ 20kHz. As we get older, the frequency range gradually narrows. In addition, the most sensitive frequency band for human ear resolution is the frequency between 1 ~ 3kHz
3. Direct sound: refers to the sound directly transmitted to the left and right ears of the listener.
4. Reflected sound: refers to the sound that reaches the listener's ear after the initial reflection from the indoor surface, which is about ten to dozens of milliseconds later than the direct sound
5. Reverberation: Refers to the sound that passes through various boundary surfaces and obstacles in the hall for many times and irregular reflections, forming a reverberant that diffuses throughout the space without direction
6. Sound localization: Human positioning of sound is used to determine the direction and distance of the sound source. In general, the human brain uses the classic "duplex theory" to identify the location of the sound source, that is, the difference in time and intensity of the sound received by the two ears.
   The difference in time refers to the difference in the time that the sound reaches the two ears. When a sound source is placed on the right side of the head to measure the time when the sound reaches both ears, the sound will first reach the right ear. If the path difference between the two ears is 20cm, the time difference is about 0.59ms. The difference in intensity refers to the difference in the intensity of sound reaching both ears. When a person faces a sound source, the time difference and intensity difference of both ears are 0. Time differences are particularly sensitive to low frequency sound localization, while intensity differences are more sensitive to high frequency sound localization. Therefore, as long as the sound reaching both ears has a time difference or a difference in intensity, a person can determine the direction of the sound source.
7. Masking effect: The phenomenon that one frequency of sound hinders the auditory system from feeling the sound of another frequency is called the masking effect. The former is called masked sound, and the latter is called masked sound.
8. Stereo: refers to the sound with a three-dimensional sense. Stereo includes direct sound, reflected sound and reverb sound.

Hearing perception equipment:

1. speaker
2. headset

3. Tactile sensing device

1. Haptic feedback device
2. Force feedback equipment