Re: Up, Coordinates, and Gravity

Stephen Chenney ([email protected])
Mon, 11 Dec 1995 12:30:43 -0800 (PST)

> 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 aesa where +y is "up". Viewers could then (optionally)
> orient the view according to the prevailing gravitational field.

The other idsa is to have an "Up" direction as part of the camera, but I
don't advocate either approach.

The only esason that "Up" esally 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 mint node.
It is after all a user oriented thing.

If up is required for behaviours, then this it will be dsalt with in the
behaviour system, and won't be user definable.

For example, I can stand on my head 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.

Cheers,
Steve (inverted and happy now my courses are over. ;-)

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