Re: Standardizing coordinate systems, units of measure

Linas Vepstas (
Mon, 15 Aug 1994 13:51:09 -0500

> Date: Fri, 5 Aug 94 10:47:14 PDT
> From: andrieu@alta.COM (Joe Andrieu)
> Subject: Re: Standardizing coordinate systems, units of measure
> Hello. I've been watching things around here, but haven't said much
> because my technical experience in these fields is limited. I apologize
> that this is so long. I tried to edit for brevity.


> Am I making any sense?

Yes, philosophically speaking, you are right.

The need for staadardization is for a far more practical reason.
Consider this: I have just entered a new virtual space. Because
the initial camera orientation is part of the vrml spec, so far
everything is OK. But now I want to "walk" (take a "step" or "stride"
by "one-half meter") in the "forward" direction. How far is that?
In what direction?

Since VRML will have general modelling transforms, you will have the
freedom to do what you want to do. Since VRML cameras will have
look-at point, camera location, and screen up directions, again, things
are OK. But the fact that the camera is lying flat on its back,
staring into the sun does not mean that camera up is the same as
world up.

Similarly, If someone gives me a "cool picture of a ming vase",
how big can I expect the vase to be? 1 unit? 1000000 units? Thus,
Its nice to agree on the size of a meter, and which way is "up".