[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:
http://www.web3d.org/membership/login/memberwiki/index.php/X3D_Physical_Units_Proposal
http://web3d.org/membership/login/groups/Korea%20Web3D%20Forum/1%28myeong%29Unit_VR.pdf
Specification changes are in the Concepts section and also Core Component
http://www.igraphics.com/Standards/ISO_IEC_19775_1_2_PDAM1_Candidate_2011_05_12/Part01/concepts.html
http://www.igraphics.com/Standards/ISO_IEC_19775_1_2_PDAM1_Candidate_2011_05_12/Part01/components/core.html
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
======================
7.2.5.5 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 7.2.5.1 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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