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Re: Definition SVG Coordinate Space?

From: Rick <graham.rick@gmail.com>
Date: Thu, 16 Sep 2010 11:27:35 -0400
Message-ID: <AANLkTi=DGa16nN9dJe3NSYpB8ZexL6pmZJNBTD9VfMyA@mail.gmail.com>
To: www-svg <www-svg@w3.org>
On Thu, Sep 16, 2010 at 10:45 AM, Rick <graham.rick@gmail.com> wrote:

> 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.

I've discovered that the inverted Y behaviour is explained in chapter 7:


There is no mention there of an angle direction.

> 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

Eeny, Meeny, Jelly Beanie, the spirits are about to speak!
        -- Bullwinkle Moose
Received on Thursday, 16 September 2010 15:28:08 UTC

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