[X3D-Public] important questions regarding Units proposal

Don Brutzman brutzman at nps.edu
Sun Jun 19 14:50:32 PDT 2011

cc: working group

On 6/19/2011 2:02 PM, npolys at vt.edu wrote:
> It appears the units proposal is now in 3.3

Original proposal and slides:


Specification changes are in the Concepts section and also Core Component

4.3.6 Standard units and coordinate systems

Standard units are modifiable from the following defaults

	angle 	radian
	force 	newton
	length 	metre
	mass 	kilogram

which in turn lead to the following derived units:

	acceleration 	length/second2
	angular_rate 	angle/second
	area 	length2
	speed 	length/second
	volume 	length3

====================== UNIT statement

X3D applications may explicitly alter the initial base units within an X3D world by inserting UNIT statements defining the characteristics of the new default base units. At most one UNIT statement shall be provided for each base unit type. Only the UNIT statements in the root file apply to an X3D world. If no UNIT statements are provided, the initial base units as specified in 4.3.6 Standard units and coordinate system shall apply.

UNIT statements contained in X3D files referenced by Inline nodes or contained in X3D files consisting of EXTERNPROTO bodies shall be used to align effected units to the base units of the root file before the referenced X3D file content is incorporated in the X3D world.

UNIT statements may only be contained in X3D worlds created for X3D version 3.3 or later (as specified in the Header statement). If a version of 3.2 or earlier is specified in conjunction with UNIT statements, the browser shall fail.

A change in a base unit is specified by UNIT statements at the top of the file preceding any element content but in the statement order specified in Organization. The form of the UNIT statement is:

    UNIT <category> <name> <conversion_factor>

where <category> is a string specifying one of the categories in Table 4.2, <name> is a string that does not contain whitespace that provides a name for the new default base unit, and <conversion_factor> is a positive double precision value that converts the new default base unit to the initial base unit specified in Table 4.2.

Dick:  shouldn't we be listing other units available in our specification?
Or at least pointing to the relevant ISO specification for these enumerations?
i couldn't find either in the proposed change.

all the best, Don
Don Brutzman  Naval Postgraduate School, Code USW/Br      brutzman at nps.edu
Watkins 270   MOVES Institute, Monterey CA 93943-5000 USA  +1.831.656.2149
X3D, virtual worlds, underwater robots     http://faculty.nps.edu/brutzman

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