Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!dali.cs.montana.edu!milton!hlab
From: mike@x.co.uk (Mike Moore)
Newsgroups: sci.virtual-worlds
Subject: Position judgement at distance
Message-ID: <1991Jun27.010103.10247@milton.u.washington.edu>
Date: 26 Jun 91 11:14:43 GMT
Sender: hlab@milton.u.washington.edu (Human Int. Technology Lab)
Organization: IXI Limited
Lines: 53
Approved: cyberoid@milton.u.washington.edu



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?

Another point of interest in relation to perspective:

                        Infinity
                          /\<----/_e
                         /  \
                        / a  \
                       /~~~~~~\            -
                      /        \           |
                     /          \          |d
                    /     b      \         |
                   /~~~~~~~~~~~~~~\        -
                  /                \       |c
                 /                  \      -

                        Observer

 o If an object has an actual width of 10 units then the apparent widths
   a and b at distances c and d depend on the angle e.  What is angle e?
   Note: This is a genuine question, not an exercise.

 o Do the same rules apply for the height of an object?

Mike Moore

* 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!

# Something else I don't want.
-- 
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