Re: ARCH: Virtual spaces and nets

John W. Barrus (
Mon, 13 Jun 1994 14:35:57 -0400

>One project that some people will undoubtedly work on is building
>virtual copies of real places (cf. Gelerntner, _Mirror Worlds_). For
>this purpose, and for the advantage of familiarity, I recommend we begin
>with Earth as a shared space and allow multiple coordinate systems,
>such as lat/long/elev, geocentric Cartesian/polar/spherical, according
>to usefulness to the given problem.
>Of course coordinate transformations will be straightforward as long
>as Cyberspace is kept connected, which it need not be.

I don't think that the coordinate systems need to be decided in advance or
enforced. One of the advantages of bits over molecules is that they can be
arranged anyway we want to link them. If I want to build a world where
rooms are adjacent and don't overlap, that should be fine. I should also
be allowed to build spaces that do overlap in space and yet I can be in one
and not the other.

One of the problems of building a very large space is floating point
precision (ask one of the engineers at Boeing who builds very large
airplanes with very small parts that must be placed precisely). Anytime we
have an environment with a large dynamic range, we are going to run into
problems. With 32 bit floats, I believe that there are about 6 digits of
precision (help me out on this one if you know exactly). That means that
objects that are 1,000,000 units apart can only be specified with accuracy
of 1 unit with respect to each other. In other words, if the UNIVERSE is
100,000,000 units across, the local coordinate system of each VRML room
will center on a 100 x 100 unit grid.

Since we can only see one page at a time in a viewer it might make sense to
allow people to build up whatever they see fit and each page only deals
with it's local coordinate system. Teleporting through a link would read
in the new page and place you at a particular place with a particular view
(specified in the link).

One persons page might eventually have a map to a bunch of other pages.
This map will define it's own local coordinate system and will bunch other
pages in a way that seems appropriate. Someone elses map will bunch them
up a different way (by creation date instead of by topic, for instance).
We shouldn't prescribe the right way to organize the data in advance.

John B.


John Barrus

Mitsubishi Electric Research Laboratories 617.621.7535 (VOICE)
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