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Subject: Re: [office-comment] Orientation problems with angles

On Sat, 2012-08-04 at 15:04 -0600, Regina Henschel wrote:
> Hi members,
> a lot of places, which use angles, are not exact enough about the 
> direction of the angle. The reason for this problem is, that the spec 
> does not define a coordinate system and therefor terms like "clockwise"

If we are talking about angles in a plane document with respect to
rotations, what is ambiguous about "clockwise"?

> or "start at 12 o'clock" are ambiguous. Sometimes a direction is totally 
> missing or even a leg of the angle is missing. To get an angle with 
> directions you need an ordered pair of rays.

A rotation in the plane is uniquely determined by its centre, the
measure of the angle and whether angles are measured clockwise or

> How to improve the situation?
> (1) Do not define own elements or attributes, when well defined one 
> exists in SVG.
> (2) Illustrate the definitions, for example as it is done in SVG for the 
> coordinate system 
> [http://www.w3.org/TR/SVG/coords.html#InitialCoordinateSystem]
> (3) Be careful to define the legs of the angle as ordered pair of rays 
> for every angle.

> (4) Deprecate an attribute, when it has often been implemented with 
> wrong direction, and define an unambiguous solution.

If implementations have bugs, those bugs should be fixed rather than the
standard changed.


Andreas J. Guelzow, PhD, FTICA
Concordia University College of Alberta

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