# Re: standard coordinate systems & units of measure

Kevin Goldsmith (kevin@unitcircle.org)
Thu, 25 Aug 1994 06:44:21 -0700

>
>Each object has slots for one or more "interfacing views", which are simply
>4x4 matrices that convert to commonly-used coordinate systems.
>
That's just over-complicating things I think. There should only be
need for one coordinate system. If you would like to use your own
coordinate system, you could put one transform before your scene that would
transform your coordinate system to the standard one.

>I can think of at least two interfacing views that would be very useful:
>
>1. A "furniture view", where 1 unit = 1 meter, one axis points up, one
>coincides with the line where the back wall of the room meets the floor,
>and the other points away from the wall. This would be useful for quickly
>placing furniture-like objects in a room so they're on the floor and next
>to the wall. (Or hanging pictures, for that matter.)
>
This would correspond to what I would call a standard coordinate
system (X-Y-Z)

>2. An "icon view", where the object must fit in a 1x1 box, one axis is up,
>one faces right, and one faces out of the screen. This would be useful
>when we have libraries containing objects of vastly different sizes, and we
>want to display a bunch of them on the screen for the use to choose from,
>in rows and columns.
>
This could be done with a simple scale by the viewing program on
the fly without too much overhead (get bounding box, scale by 1/box).

>Other interfacing views can be defined as the need arises for different
>domains, e.g. "chemistry view," using angstroms, "galactic view", using
>light-years, "Sim City view," where 3 units = 1 city block, etc.
>
again, too complicated. Also, how am I supposed to know where all
of my models will end up and all the possible views that will be needed?

>The idea is that the interfacing views encapsulate whatever native
>coordinate system the designer has chosen to use for implementing the
>object; the native coordinate system should be inaccessable outside the
>object's definition. So, an object designer can use whatever coordinate
>system is convenient.
>
see again what I said above. this could be taken care of by one
transform at the beginning of the model's definition.

>Also, support for any particular interfacing view is optional. For
>example, someone designing a starship object would want to leave the
>furniture view out, which would immediately indicate to users who
>accidentally try to put a starship in a living room that they're doing
>something silly. (Of course, you can always use another view and scale it,
>if you want to put a starship in a living room anyway - a model starship,
>perhaps.)
>
That sort of makes the interfacing view unnecessary anyway.

Kevin

kevin@unitcircle.org zine@unitcircle.org