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Definition SVG Coordinate Space?

From: Rick <graham.rick@gmail.com>
Date: Thu, 16 Sep 2010 10:45:52 -0400
Message-ID: <AANLkTinqwru+q4nH_SxngF526j8NHnE24Vvyu6Sfm_+f@mail.gmail.com>
To: www-svg <www-svg@w3.org>
Hello SVG Working group

In writing a document regarding coordinate spaces for some server software,
I find that I cannot locate the definition of what constitutes an angle in
SVG.

Also, the only place that I see it stated that vertical for a Y coordinate
is negative is in the magic flip definition for glyphs, and it seems likely
that that most excellent and useful aspect of SVG is under threat due to the
persistence of a vocal minority.

http://www.w3.org/TR/SVG/fonts.html#SVGFontsOverview

My thoughts are this information should be stated in the definitions for the
angle and coordinate data types in chapter 4.

http://www.w3.org/TR/SVG/types.html#DataTypeAngle
http://www.w3.org/TR/SVG/types.html#DataTypeCoordinate

I'm not certain that there are any concepts that require the notion of a
zero angle direction.  Unrotated simple text runs left to right, but not all
text does.  I can't think of a concept in SVG where an angle is not
relative.

Nevertheless it might be useful to define what direction zero is.  In GIS it
is up, in Cartesian space it is to the right.

The following concepts are true for SVG, conflict with Cartesian concepts
(so they are not intuitive), and should be stated in the data definitions:

 - Angles are measured in a clockwise direction.
 - Y ordinates increase from top to bottom.

Please clarify this in the data type definitions.

-- 
Cheers!
Rick
Received on Thursday, 16 September 2010 14:46:24 GMT

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