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

• From: "Dennis E. Hamilton" <dennis.hamilton@acm.org>
• To: "'Andreas J. Guelzow'" <andreas.guelzow@concordia.ab.ca>, <office-comment@lists.oasis-open.org>
• Date: Sat, 4 Aug 2012 20:07:26 -0700

```Are you not assuming the orientation of the +X and +Y axis directions and the placement of the origin from the perspective of the viewer in making that statement?

- Dennis

-----Original Message-----
From: Andreas J. Guelzow [mailto:andreas.guelzow@concordia.ab.ca]
Sent: Saturday, August 04, 2012 17:27
To: office-comment@lists.oasis-open.org
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
counterclockwise.

>
> 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

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

```

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