Immersive Virtual Heritage applications: Conceptual bases
Lesson 5
Virtual Reality Properties
The mental feeling of being in a virtual space (not necessarily synthetic – can be experimented also in books and movies). It is related to the user involvement.
1
Presence
The user capacity to modify the environment and to receive from the environment feedbacks to his/her action. It is related to the realism of the simulation.
The physical feeling of being in a virtual space, at a sensorial level, by means of interfaces. It is related to the perception of the virtual world as actually existing.
Immersion
Interaction
Oversimplifying, interaction and immersion can be considered as variables, placed on a two perpendicular axes, which concur to create the sense of user presence.
The stronger emotional involvement triggered by immersion helps the establishment of perceptual mechanisms that, by increasing the user’s ability of interfacing with information, facilitate an effective conveying of contents.
There are also numerous subjective factors involved in user presence perception.
Presence in Virtual Environments
2
Presence in Virtual Environments
Place illusion
The strong illusione of “being in a place” in spite of the consciousness of being not actually there.
Immersion represents the boundaries within which the place illusion can take place.
For this to be possible, it is necessary that a set of coherent sensorymotor events exist so that the user actions can significantly and consistently introduce changes in the environment.
3
Presence in Virtual Environments
Plausibility
Is related to what is perceived: the illusion that what is happening in the Virtual Environment is actually happening, together with the awareness that it is not.
“Public speaking”
People anxious for public speaking are anxious (as retrieved from physiological measurementes and evaluation questionnaires) also in front of a public of virtual humans. If the public shows boredom or intolerance, anxiety grows noticeably.
An immersive Virtual Environment requires a strong presence feeling, in order to make the interaction natural and to improve user’s perception of it. This feeling is determined by 3 factors:
Quality of sensorial information (modeling and rendering)
Sensors mobility and control
Environment control
4
Presence in Virtual Environments
Lo-quality sensorial info
Low comfort sensors
High environment control
Low environment control
High comfort sensors
Hi-quality sensorial info
5
Virtual Environment Data Flow
According to David Zeltzer, one cannot talk about presence without first addressing a discourse about the goal an application sets for itself.
What does one want to simulate?
What senses are being stimulated?
Starting with these questions, one needs to identify the sensory channels that an experience engages in order to allow the user to immerse himself in the virtual environment.
?
6
Visual channel
In order to see a virtual environment, one needs visual output peripherals such as screens, head-sets or projectors.
Monitors return a two-dimensional representation of environments (even 3D ones). This is because the screen adopts a single point of view: each eye provides a 2D perspective view of the world; combining these two perspectives forms a stereo pair that inherently contains information about the three dimensions.
So, an important first distinction is this: the screens we generally see are two-dimensional representations of three-dimensional environments. An effectively three-dimensional representation is one enabled, for example, by VR hardware (HMD) in that, by generating an image for each eye, thus two different viewpoints, it is able to return a three-dimensional visualization of the environment.
R. eye
1 point of view (monoscopic) = 2d visualization
Screen
3D object
L. eye
R. eye
L. screen
3D object
L. eye
R. screen
2 point of view (stereoscopic) = 3d visualization
7
Depth cues for 3D enviroment
Shading
Provides info about the orientation and the position of surfaces related to a light source
Perspective
An object with a known size can provide information about its depth depending on its apparent size
Occlusion
If an object occludes another object it is perceived as closer
We can perceive the three dimensions thanks to a series of information (depth cues).
To effectlively simulate a 3D environemnt, it is necessary to provide as many depth cues as possible, or at least the most significant ones.
Parallax
Objects place at different distances move with different apparent speed
Important depth-cues
8
Depth cues for 3D enviroment
Field of view
Human field of view is about 180°x120°. The presence of a border at the edges of a stereo image “destroys” the 3D illusion (monitors have FOV=35°x27°)
Dynamic perspective
When we move, even slightly, our point of view, the perspective of the world changes. We need to track position and orientation of our head to correctly update the perspective
Depth on field
Objects at different distance are focused differently
Non-visual clues
Provide additional information, like the ones coming from the vestibular apparatus or kinaesthetic data from the neck etc
Important depth-cues
9
Acoustical channel
Another essential channel for ensuring user immersion is the audio channel.
Audio can be transmitted in different modes to provide more or less opportunities for realism as needed.
Modes
Sounds are distributed over two channels. A virtual source can be created, but only on the line connecting the two speakers
Monophonic
Sound comes from only one channel; it is not possible for the user to understand its direction of origin.
Multichannel speaker arrays
Channels expands the space in which the virtual source is placed
Stereophonic
10
11
Other channels
Motion feedback
Olfactory channel
Taste rendering
Haptic interfaces
Type of interaction
Direct: the user interacts directly with the VE
Mediated: the user interacts with the VE through an avatar
First person (“Quake-like”)
Third person (“Tomb Raider – like”)
The interaction can be forced by the hardware
CAVE: direct
HMD: mediated, first person
Monitor: mediated, first/third person
12
Interaction in virtual environment
Interacting means having the ability to change the environment one is in. Especially, to interact with a virtual environment, one needs tracking and motion-capture devices so that the computer can translate user-given input into computer language.
Metaphors reproduce concepts, known by the user in a certain context, in order to transfer this knowledge in a new context related to the execution of a task.
13
Interaction metaphors
The easiest way for a human being to behave in a VE is to behave like he/she was in a real environment. This is not always possible or suitable due to technological constraints or need of more advanced options in order to allow effective performances in accomplishing tasks
Selection/manipulation
Navigation
A good metaphor must be:
Representative of the task
Compatible with the user knowledge
Compatible with the physical constraints of the interface
Thank You!
Giovanni Giuliodori
giovanni.giuliodori@santannapisa.it