From: Pablo Figueroa [pfiguero@cs.ualberta.ca]
Sent: Wednesday, December 13, 2000 2:11 PM
To: Doug Bowman
Cc: 3dui List
Subject: Re: description of an IT

Hi all,

Two comments:  
- Doug, great you are brave enough to talk about this topic that I really
like! ;->

- From your example I've got that the requirements you propose for a
language for ITs are that it should be precise and human-understandable.
if these are the requirements, I think the pseudocode is maybe not precise
enough neither easy to understand. It is not easy to find what are the
unknown details in the pseudocode, despite there are some, and it was
easier for me to read the textual description than the pseudocode.

It is difficult to find one language with these two characteristics.
Ideally, it might be nice to have more than one way to understand an IT,
maybe several formats. For example, it might be nice to have for any IT
the following:
- A textual description in a nice format (latex?), similar to what you
find in a paper. 
- A program-readable interface (IDL?, XML?) that can be implemented in
several languages and frameworks.
- A source-free implementation in a well known framework (Java3D?) that
shows how it works, it is precise enough, and it is related to the
program-readable interface.

So, in the case of GoGo, the description can be the following:

Text:
(A short description from Poupyrev's paper)
Program-readable Interface:
(Something like what I wrote in a previous email, without the formal
invariance.)
Source-free implementation
(It is possible define a framework in java3D that allows any author to
add a new IT)

Despite this description means more work, it fulfills your
requirements (and I like it... ;->)

From your pseudocode I have just one concern... you describe at the end
the feedback for selection highlighting... I wonder if this constrains too
much the selection IT... It is possible to have other types of feedback,
with the same selection mechanism...

Best Regards,

-------------------------------------------
Pablo Figueroa              pfiguero@cs.ualberta.ca
PhD Student                 http://www.cs.ualberta.ca/~pfiguero
University of Alberta

Relax ... God is in charge  
-------------------------------------------

> Greetings!
> 
> I see that no one was brave enough to accept my challenge to
> describe your favorite interaction technique. So, I thought
> I would give it a shot. Here's a description of the Go-Go technique
> (only the selection part, not manipulation).
> 
> Remember that my goal here is for this to be understandable,
> yet precise.
> 
> ---------------------------------------------------------------------
> // declarations and definitions
> constant GOGOTHRESHOLD = 0.3 meters;
> 
> object headTracker;
> object handTracker;
> object virtualHand;
> object selectableObjects[N];
> 
> 3Dpoint headPosition;
> 3Dpoint handPosition;
> 3Dpoint virtualHandPosition;
> 3Dpoint torsoPoint;
> 
> float virtualHandDistance;
> vector virtualHandVector;
> 
> // all of this should happen before every frame is rendered
> headPosition = world coord. position of headTracker;
> handPosition = world coord. position of handTracker;
> 
> // assuming y is the vertical axis
> torsoPoint = (headPosition.x, headPosition.y - 0.5, headPosition.z)
> 
> if(distance(torsoPoint, handPosition) <= GOGOTHRESHOLD)
> 	then virtualHandPosition = handPosition;
> 	move(virtualHand, virtualHandPosition);
> 
> else
> 	virtualHandDistance = GoGoFunction(distance(torsoPoint, handPosition));
> 	virtualHandVector = handPosition - torsoPoint;
> 	normalize(virtualHandVector);
> 	virtualHandPosition = torsoPoint + (virtualHandVector *
> virtualHandDistance);
> 	move(virtualHand, virtualHandPosition);
> 
> for i from 0 to N
> 	if(highlighted(selectableObjects[i])
> 		unhighlight(selectableObjects[i]);
> 	if(intersects(boundingBox(virtualHand), boundingBox(selectableObjects[i]))
> 		highlight(selectableObjects[i]);
> ---------------------------------------------------------------------
> Thoughts and comments are welcome. Is this a good level of description?
> What's missing? What details are irrelevant? I didn't include many
> comments on purpose so that you could see if the description itself is
> understandable.
> 
> Best,
> Doug
> 
> --
> Doug A. Bowman, Ph.D.          (540) 231-7537
> Assistant Professor             bowman@vt.edu
> Computer Science        www.cs.vt.edu/~bowman/
> Virginia Tech
>