Re: Standardizing coordinate systems, units of measure

Linas Vepstas (
Thu, 4 Aug 1994 11:26:37 -0500

> From: "Gavin Bell" <>
> Date: Tue, 2 Aug 1994 18:27:35 -0700
> Subject: Re: Standardizing coordinate systems, units of measure
> So, imagine a user visits your galactic "page" (we do need jargon for
> this...).

Haw about "group"? (I'm thinking ala phigs edit group). Its not
an object, its not a collection, its not a composite (what inventor
calls "SoGroup", I'd like vrml to call a "composite" -- since thats
closer to what the rest of the world calls them).

> I tend to think of this as the "size of observer" problem-- if I'm
> looking at a galaxy, I'd better have legs that are light years long to
> move me around fast enough to see anything interesting. So, I'd be
> inclined to encode the size of the observer into the camera's
> information (side note: if using Inventor, I'd wedge this into the
> focalDistance field of the camera, reasoning that when walking around I
> tend to focus farther ahead than an ant).

The point of this is lost on me --- if the observer wants to grow or shrink,
can't they simply scale the world ??

The real problem is gestural one -- if I sweep the mouse, (or press on a
FakeLabs Boom button), how far do I advance? I assume that most well
designed viewers will move you by a meter or two -- and also provide controls
to modify that speed. (and to change camera height off the floor, or change
overall observer size, etc.) Flyby viewers would have correspondingly greater
velocities -- all measured in meters per second, or meters per gesture.
I don't see that this calls for any sort of standardization.

The only limitation/caveat/directive is for all "group" designers to
understand that the dimensions of thier "group" will be measured in
meters, and that they should set up scale matrices appropriately if they
wish to work in another unit of measure.