From: good@baviki.enet.dec.com (Michael Good)
Subject: Re: Position judgement at distance
Date: Thu, 27 Jun 1991 14:16:02 GMT
Organization: Digital Equipment Corp. Presence Laboratory



In article <1991Jun27.010103.10247@milton.u.washington.edu> Mike Moore 
<mike@x.co.uk> writes:

>My armchair virtual world program has a problem....
>
>I've picked up an object (a pyramid) and now I want to put it down so that
>it rests on top of another object (a cube).  I don't want point-of-view of
>the user to change as the operation is done.  The visual 3d feedback given
>by the system can confuse the user as they have no idea of scale (i.e.
>unless the user has actually walked up to each object and examined it,
>s/he has no idea if the cube is large and far away or small and close by*).
>
>I was thinking of using a shadow which appeared underneath the pyramid and
>deformation of the shadow as it travelled over the cube would inform the
>user of the pyramids position relative to the cube.  This implies that the
>light source generating the shadow must always be at a defined point,
>preferably immediately above each object#.
>
>Does anybody have any ideas about how to further progress this?  Or good
>books which discuss various methods of giving distance and relative
>position feedback to the user?
>
>[Stuff deleted]
>
>* I know that I can get away from this problem by having some kind of
>checker-board floor, but I don't *want* a checker-board floor!


You may not want to use a checkerboard floor, but some type of textured
ground (it can be more subtle than a checkerboard if your system has
the graphics capability to display it quickly) is perhaps the most
straightforward and ecological approach to solving this problem.
Distance perceived along the ground is visible; distance perceived
through space is not.  See James Gibson's "The Ecological Approach
to Visual Perception", pp. 117 and 160-164.

Michael Good
good@baviki.enet.dec.com