MOVING OBJECTS IN SPACE :
EXPLOITING PROPRIOCEPTION IN VIRTUAL ENVIRONMENT INTERACTION

What is Proprioception ?

A Person's sense of the position and orientation of his body and its parts.

Problems in Interaction in Virtual Environment

• Difficult to make precise movements and applications
• No Haptic Feedbacks - no physical constraints , no work surfaces to rest or align at.
• Input information much less than in real world .
• Modifications
• Audio.
• Measuring
• Annotation.
• Limited Precision- Not exact but approximate coarse manipulations, due to lack of haptic/audio feedback.
• No unifying framework for Interaction.

Using Proprioception.

• Direct Manipulations
• Physical Mnemonics.
• Gestural Actions.

Interaction Techniques

1. Direct Manipulations

Scaled World Grab.



World automatically scaled down about user's head every time he grabs an object and scaled back up when he releases it.





Advantages :

• Direct mapping between hand and object motion.
• Provides finer angular precision of motion.
• Takes advantage prorioceptive information.
• Doesnt have to fly , walk to reach objects .





Other features :

• User Unaware of Changes.
• Enables viewing big objects from sides.
• More convenient than laser beams , which are good only for radial rotations or translations along the beam.





Scaled world grab for locomotion

• User can reach any visible destination in a single grab operation.

2. Physical Mnemonics

Storing of Virtual Objects and Control relative to the User's body.

(a) Pull Down Menus

Menus stored somewhere relative to the Users' body, in a position that aids the user in recalling it's position eg.


Viewing Properties -- stored by the head.

Manipulating Objects -- can be stored by user's hands.

(b) Hand held Widgets

Having a set of widgets to manipulate the object remotely rather than having them on the object(Object Bound Widget)

Hand Held Widgets are preferred over the Object bound widgets due to :

• The object bound widgets have to be located visually , as opposed to hand held widgets which use Proprioceptive method.
• User does not have to walk up to the object.
• Reduces visual clutter . A common widget for all objects , instead of each having its own set of widgets.
• Eliminates obscuration of an Object by its own widget.

(c) FOV - Relative mode switching

One knows when user's body is in FOV.

Can be used to switch mode between occlusion selection and Ray Casting.



---

---

(3) Gestural Actions

(1) Head Butt Zoom -

Enables a user to switch from global view to local close up view, by moving in and out of a window formed between the two hands of the user.
The position of the window is infront of the user, at the position of his hands.
The zoom factor is dependant on the size of the window made.

The advantages this method provides :

• Users do not need to interrupt any other process, in order to set or change a Zoom factor.
• A good use of screen space is made, as the screen is not be divided for different scale scenes.

(2) Look-at menus

Besides being intuitive ,gives the user the abilty to use the input device for other things , while making a selection in this menu.

---

(3) Two-handed flying

• Direction of the flight is specified by the vector between the users' hands.
• Speed Proportional to the distance between them.

(4) Over the shoulder deletion

• Throwing at the back as a normal action.
• Retrieving the last object deleted by simply reaching over the shoulder and grabbing it.

Its utility could be explained in terms of ease of remembering the metaphor, and not using any menu space or buttons .

(1) Virtual Object Docking

Goal :

Study differences and find out User Preferences between manipulating objects that are co-located with user's hands and objects at a distance.

Similar exercise was carried for 3 different cases, for Object located at the user.s hand position ( scaled grab), then located at a fixed distance ( laser beam interaction) and located at a variable distance (extender grab ).

Task :

Target shapes transparent and red in color were to be aligned with opaque blue colored cubes. These blue cubes were either located at User's hand position or at a distance, and then the time taken by the user to align the two cubes was noted.

Each user did 216 trials , ie 36 docking trials /test X 3 tests/block X 2 Blocks

Results

Experiment Results

• Shows that it took the least amount of time to align in the case of the scaled grab position.

Questionaire Results

Note : The points are given on the scale of -3 of 3

• The Questionaire results also indicate a clear preference for the colocated mode of manipulation .

(2) Virtual Widget Interaction

Goal :

Find out the difference between using a hand held widget using Proprioception techniques and using a widget system floating in Space. One of the goals was to see to what extent can the user take advantage of this technique.

Task :

The Users were expected to carry out a 3 step procedure , once for the hand held widget and then for the widget which was floating in the air , at a fixed distance.

In the case of the hand held widget , the widget moves along with the users hands. In the other case they remain fixed irrespective of the users movements. For both the cases , the Users were supposed to first align a 3D Cursor to one of the 6 spheres on the widget , then align it to an arbitrary object in the space , and finally bring it back to align it with the widget , without any visual feedback.

The positional accuracy of the user , in aligning the cursor was noted , and evaluated.

Results:

Experimental Results :

The following table shows the mean positional accuracies in the 2 cases , and the results clearly show , that the hand held widget gave more accuracy in alignment.

Questionaire Results:

These results also indicate the relative preference for Hand Held widget System rather than a widget system away from the body.