Yes I think that coordinate system definition needs to be in the
specification too. Great idea. Right-hand rule is of course essential.
> Another thought is what orientation should the coordinate
> system be in. I realize why people like the X-right, Y-up,
> with Z perpendicular to the screen, mostly because they are
> used to seeing this on graph paper and it extends very nicely
> to the screen. I think that we need to make a paradigm
> shift when we go into 3-d, and rather than making the global
> cartesian system conform to the 2-d stuff we have been using,
> something intuitive to the 3-d world would be appropriate.
> My feeling on what may be more explainable to the average
> person coming into 3-d is X-forward, Z-up, now using the
> right hand rule we can say Y is to the left. The reason
> this makes sense to me is I can look at the ground I am
> travelling over in the 2-d sense of x-y and add the height
> with z. Just some thoughts.
This matches what I've been saying and is very clearly expressed.
An additional note here: the description of forward/up/left is from
a default perspective of a camera looking along the positive X axis, level
to the X-Y plane. The other essential is that X and Y axes define the
ground plane, not Z. Anything you care to say about camera direction is fine
after (a) right-hand rule, and (b) X-Y plane level is agreed upon.
The corresponding scene graph has X-Y grid coordinates for location over the
ground and Z coordinate for height/altitude. This matches (or is directly
compatible with) all of the major physically based conventions for defining
location.
I recommend we put (a), (b) and (c)=predefined camera viewpoints
(a la the Palladium) in VRML 1.1 or 2.0. In order to provide easy
compatibility with other coordinate system definitions, a handful of
different transformation nodes which convert from one coordinate system to
another might be useful to have in the FAQ (or as selectable browser options).
all the best, Don
--
Don Brutzman Naval Postgraduate School, Code UW/Br work 408.656.2149
Monterey California 93943-5000 USA fax 408.656.3679
AUV Underwater Virtual World ftp://taurus.cs.nps.navy.mil/pub/auv/auv.html