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Re: Arc Segment Implementation Notes ...

From: Helder Magalh„es <helder.magalhaes@gmail.com>
Date: Thu, 26 Jun 2008 12:17:43 +0100
Message-ID: <2a1ddf8a0806260417i456599beo24bd5684d1de3757@mail.gmail.com>
To: "Dr. Olaf Hoffmann" <Dr.O.Hoffmann@gmx.de>
Cc: www-svg@w3.org

> I think, the missing arc commands are more related to a tiny profile than to
> version 1.2, because they are not available in SVG tiny 1.1 too:
> http://www.w3.org/TR/SVGMobile/#sec-shapes

Agreed. :-)

> As many other shapes elliptical arcs cannot be exactly expressed with
> cubic curves.
> Depending on the accuracy requirements, an author can compute
> a set of cubic curve fragments to replace an elliptical arc approximately.
> Typically a good approach is to demand that position and derivates fit
> together at the end of cubic curve fragments joined together to an
> approximation of an elliptical arc.
> How many curve fragments are needed to get the desired
> accuracy obviously depends on the requirements of the author,
> therefore there cannot be a general rule to do this approximation.
> However, the rule described above is an even more general
> rule how to approximate any continuously differentiable  curve
> with a cubic curve, but this needs some calculations, either analytical
> or numerical.

Sounds well. I'd challenge you to marsh up these suggestions into a
cleaner writing (possibly with already referred arc implementation
notes [1] look) and posting them here (or in a separate thread),
potentially accompanied by relevant illustrations. This would allow
the WG to more easily pick this up and (possibly) add to a (new?)
specification annex, labeled "SVG Full to Tiny content migration" or
equivalent. :-)

> I needed for some reasons already a cubic curve replacement
> for an ellipse, circle and some other shapes like spirals, atomic
> transition dipole moment shapes, therefore I already did this with
> a small PHP script analytically or numerically and it is not really
> a big issue if one is familiar with basic analytics.

Could you share it? Reinventing the wheel is not one of those tasks
anyone wants to deal with - if this would be publicly made available,
it would probably help many to prepare for SVG Tiny content. ;-)

As a side note: how about creating a "SVG Full to SVG Tiny path data
converter" tool? It would parse the path data and replace the arc
commands with your PHP script output. Of course a general "SVG Full to
SVG Tiny" content converter would be even more interesting, which
could then warned about possible content conversion limitations. I
wonder if I'm also proposing a wheel reinvention and such tool is
already available...? :-D

Best regards,

 Helder Magalh„es

[1] http://www.w3.org/TR/SVG11/implnote.html#ArcImplementationNotes
Received on Thursday, 26 June 2008 11:18:19 UTC

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