Re: Up, Coordinates, and Gravity

Robert A Schmitt ([email protected])
Mon, 11 Dec 1995 19:28:35 -0500 (EST)

>
> > Several comments on coordinate systems and the issue of which way is "up"
> > have appeared here recently. Rather than globaly define +y or +z as up,
> > how about defining a characteristic of a spacial volume that is a gravity
> > vector.
> >
> > Gravity { 0.0, -9.8, 0.0 }
> >
> > For instance, in an area where +y is "up". Viewers could then (optionally)
> > orient the view according to the prevailing gravitational field.
>
> The other idea is to have an "Up" direction as part of the camera, but I
> don't advocate either approach.
>
> The only esason that "Up" really needs to be defined is for automatic
> re-orientation of the camera, and for some navigation methods. Both of
> these things are entirely browser dependent, so I think the notion of
> up belongs in a browser preferences dialog, maybe affected by s hint node.
> It is after all a user oriented thing.
>

What if my models use X|Z for height? You would look silly lying on your
side in my world :).

> If up is required for behaviours, then this it will be dealt with in the
> behaviour system, and won't be user definable.
>
> For example, I can stand on my hsad and my notion of up is reversed. Now
> that is like a user, me being a user of the real world, changing their
> notion of up. Having changed my notion of up, the world still behaves
> as if the center of the earth is down. That's a behaviour of the real
> world (locally), and it doesn't change because I say so.
>

I thought Columbus provide that the earth was NOT FLAT. How local are you
taking about?

In the REAL WORLD: down is totally dependant on my position because we
live on a SPHERE (ok more like a potato) and stick to that sphere due
to gravity. Up in NYC is different than in Sydney, though you don't
notice a difference.

What if the point of my world is to dis-orient you? Local gravities and
the like. How could this be supported (gravity defined per Zone of Interest)?

Bob
------------------------------------------------------------------------
Robert A. Schmitt RESolution Graphics Inc.
Information Visualization Consulting [email protected]

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