Sense

“The most overlooked advantage of owning a computer is that if they foul up there’s no law against whacking them around a bit” – Eric Porterfield

Computers have no emotional feelings, and even if they did they would hardly have any idea what we were doing to them anyway.

Making a Sensible Computer

Head Tracking

Not only does head tracking allow the computer to draw the world, it also tells the computer where we are and what we are looking at.

Gaze-based selection involves using the direction the head is pointing to select objects.
Gaze-based navigation involves using the direction the head is pointing to determine where to go next.

Where are we?

An augmented reality system uses the physical world as its environment, but a virtual world will most likely be different from the virtual world.
Current head tracking systems have limitations to their range.
Even if they had no range, projection display systems and wireless communications limit the range within which we can deliver visual input.
However, even with unlimited range, it is not practical to allocate as much space in the real world for freely moving in the virtual world.

This poses a problem for navigating to other locations within the virtual world.

Haptic Navigation Techniques

Realizing the goal of accurately reproducing the sensation of moving within an environment is a difficult goal.
While the reproduction of 3D visuals based on head motion is relatively straight forward, reproducing very complex motion of walking is much more difficult.
The very physical nature of the activity means that the device must be a mechanical device and includes all of the typical problems associated with haptic devices:

• expensive to build
• difficult to calibrate and maintain
• their inherent bulkiness limits their ability to create a truly natural experience
• any device that interfaces directly with motion and balance will have serious safety issues

Examples include:

• spinning based machines
• uni-directional treadmills
• stair step machines
• omni-drectional treadmills
• OmniTrek
• TorusTreadmill
• CyberSphere

Software Navigation Techniques

The practicalities of haptic systems force us to consider less intuitive navigation methods.
These methods are very practical and useful for navigation, but they disrupt attempts to make the interface invisible.

• walking simulation
• the user mimics the motion of walking
• because they not adequately reproduce the sensation of walking, users often are inclined to opt for a joystick instead
• legs must be tracked
• joystick based navigation
• people are familiar with this technique from video game usage
• can be combined with 3D wand tracking for more control
• “point-and-move” is the predominant CAVE navigation method
• user is navigated in the direction the wand is pointed
• moving the joystick forward navigates forward and moving the joystick backward navigates backward
• moving the joystick left or right changes the direction that the CAVE is pointed
• the amount the joystick is moved determines the speed of motion
• changing the direction of the CAVE should not be necessary in a fully surround setup - VRAC
• gaze-based navigation
• leaning forward can control motion
• often disliked by users because they are forced to keep their head pointed in the direction of travel
• gesture-based navigation
• “grabbing-air” method similar to pulling on a rope
• moving the hand in the direction of desired travel can indicate both direction and desired speed

Can you see me?

Walking simulation systems and/or gesture based systems require tracking parts of the body that may prove awkward for traditional tracking setups such as magnetic systems.

Can use computer vision techniques to estimate the motion of the legs or to follow simple gestures.

Some simple techniques can give a rough estimate of the location of the user and their limbs:

• infrared cameras are inexpensive and can give a silhouette of the body against many backgrounds - VideoPlace
• a simple algorithm based on light intensity or surface area of the body can determine depth and position
• these techniques are useful when the input from the body to the system does not need to be exact - Maya

Can you feel me?

Although truly flexible haptic systems are many years off, physical props can replace them in specific situations.

• using a tablet for selecting interface items or drawing can be useful
• projection based systems often use a transparent surface
• a tablet display can even be introduced into the environment for a higher resolution interface
• actual props with tracking devices attached to them can be used
• objects in the virtual environment such as blocks, tables, etc. can be introduced into the CAVE
• since the objects must be registered with the virtual space it is unlikely that software navigation techniques can be used in conjunction
• introducing a mixture of virtual and real objects is often called mixed reality
• the most successful immersive system ever created uses physical props to make the interface between the user and the virtual world truly invisible – Flight Simulation