Coordinate systems have much more variation but at least follow RHR.
Most common is
thumb east positive x
index finger north positive y
middle finger up positive z
Origin is typically an object's center of gravity in relative (body)
coordinates, or a local point at the surface of the earth in world
coordinates. After that there are a number of world coordinate
reference systems possible. Some are round and some are flat and some
are geoids and some are none of the above.
May I suggest that we make physically-based world models correspond to
a flat local earth's surface, and agree on a convention for a
comment field or Info { } node that includes latitude and longitude
(and perhaps altitude/depth). Since comment fields are not persistent
(browsers can dump them) an Info node seems appropriate. Example:
Info { "Latitude 35.0 North, Longitude 122.0 East" } # seconds:minutes ?
Flat local earth is not so bad. When you are at the beach and look at the
horizon, that is how far you can see before the Earth's curvature has
an effect. On land this is hardly noticeable at all since tall objects can
be seen a long way and occlusion/level of detail are more predominant
effects. (If your scene is the globe you might want to stay spherical.. :)
As we get into behaviors I expect we will need to agree on a convention to
put Euler angle or quaternion rotations at the "top" of a scene to properly
orient it with respect to world coordinates. The same type of convention will
be needed for rotatable/translatable subgraphs within the scene, if
those rotations/translations are to be capable of receiving externally
generated values as inputs. Suggestion: pick label name conventions.
Precaution: this is not the same as (and not necessarily independent of)
camera original location. Using "Origin" as an example name convention:
DEF Origin Separator {
# scene graph here ...
}
For even more detail see http://vrml.wired.com/arch/0500.html
Usual bottom line: we need to keep things as simple as possible, and
meanwhile remember reality so that we can later link everything together.
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