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

["Dennis E. Hamilton" <dennis.hamilton@acm.org>]

I believe I can safely say that all vector characterizations on a Cartesian plane are relative to a frame of reference.  Directions of translation and rotation are relative to that frame of reference.  (Clockwise is anti-clockwise when viewed from "behind", when viewed in a mirror, etc.)

Asking for identification of the axes and their directions for the frame of reference is another way of nailing down what that frame of reference is.  Then how that is projected onto the surface of the document as presented to a viewer can be made precise.  Up, down, left, right, front, back, clockwise, etc., have no meaning until there is agreement on what the frame of reference is.  (There is a similar problem in ODF when certain characteristics are dependent on the assumed writing direction and the relationship is underspecified or ambiguously described.)

 - Dennis

PS: In one of the early, famous anthologies of English-language science fiction stories, there is a short story about a robot craft that is landed on Venus.  A Venusian manages to enter the craft and that activates a self-destruct mechanism.  The remote operators need to find a way to tell the Venusian how to press the button on the left of the console that disables the countdown and *not* press the button on the right of the console, which activates the destruction immediately.  I forget how they managed it.  

-----Original Message-----
From: robert_weir@us.ibm.com [mailto:robert_weir@us.ibm.com] 
Sent: Tuesday, August 07, 2012 07:13
To: office-comment@lists.oasis-open.org
Subject: Re: FW: [office-comment] Orientation problems with angles

For relative rotations (relative to current placement) all you need to do is specify the amount of rotation and direction (clockwise versus counter-counterclockwise).  The coordinate system is irrelevant. 

For absolute positioning, e.g., "place the arrow so it is pointed at +45 degrees" then you need more context. 

In any case, I've added this issue to JIRA (OFFICE-3775) so we can track any proposed resolution there. 

-Rob 

"Dennis E. Hamilton" <dennis.hamilton@acm.org> wrote on 08/05/2012 11:46:03 AM:

> From: "Dennis E. Hamilton" <dennis.hamilton@acm.org> 
> To: <office-comment@lists.oasis-open.org>, 
> Date: 08/05/2012 11:47 AM 
> Subject: FW: [office-comment] Orientation problems with angles 
> 
> [Sorry, sent from an unrecognized address before.]
> 
> -----Original Message-----
> From: Dennis E. Hamilton [mailto:himself@orcmid.com <mailto:himself@orcmid.com> ] 
> Sent: Saturday, August 04, 2012 23:36
> To: 'Andreas J. Guelzow'; 'office-comment@lists.oasis-open.org'
> Subject: RE: [office-comment] Orientation problems with angles
> 
> Help me understand this better,
> 
> From the perspective of the observer that you refer to,
> 
> Where is the origin, and in which directions are +X and +Y from that
> origin?  And from which axis (+X, +Y, -X, -Y) extending from the 
> origin does this clockwise motion originate that opens the angle 
> with respect to which the gradient vector is oriented?
> 
>  - Dennis
> 
> -----Original Message-----
> From: Andreas J. Guelzow [mailto:andreas.guelzow@concordia.ab.ca <mailto:andreas.guelzow@concordia.ab.ca> ] 
> Sent: Saturday, August 04, 2012 22:30
> To: office-comment@lists.oasis-open.org
> Subject: RE: [office-comment] Orientation problems with angles
> 
> On Sat, 2012-08-04 at 21:07 -0600, Dennis E. Hamilton wrote:
> > 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?
> 
> I don't see how the coordinate system has anything to do with
> "clockwise" nor how the placement of the origin is involved in a
> clockwise rotation. The clocks I know have no coordinate system nor an
> origin (just a centre of rotation). The meaning of "clockwise" is
> uniquely determined once we know on which side of the plane the viewer
> is. And in the case of office documents this is always clear. 
> 
> Andreas
> 
> > 
> > -----Original Message-----
> > From: Andreas J. Guelzow [mailto:andreas.guelzow@concordia.ab.ca <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 <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
> > 
> > 
> 
> -- 
> Andreas J. Guelzow, PhD, FTICA
> Concordia University College of Alberta
> 
> 
> -- 
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