Re: Circular paths

Am 03.01.2011 um 23:42 schrieb ddailey:

> In the following:
>  
> <svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" >
> <path d=" M 200,300 a 100,100 0 1 1 .0001 0 z " fill="white" stroke="black" stroke-width="3" />
> <path d=" M 400,300 a 100,100 0 1 1 .00001 0 z " fill="white" stroke="black" stroke-width="3" />
> </svg>
>  
> Opera, Chrome, IE+ASV all show one circle. Firefox shows two. I would prefer to see two.
>  
> It would be nice if even
> <path d=" M 400,300 a 100,100 0 1 1 epsilon 0 z " fill="white" stroke="black" stroke-width="3" />
> for the limiting case when epsilon=0.
>  
> cheers
> David

The specification wants us to omit the elliptical arc segment, if the endpoints are identical: http://www.w3.org/TR/SVG/implnote.html#ArcOutOfRangeParameters.
 I guess the reason is the algorithm at F.6.5 Conversion from endpoint to center parameterization. If both endpoints are identical, (x1' y1')^T and (cx' cy')^T are both (0 0)^T, the null vector. So teta1 is the angle between (1 0)^T and (0 0)^T (per definition 90 degree). And theoretically delta teta is 90 degree as well (angle between null vector and any other vector is 90 degree). So you won't end up on a circle at all.
Please correct me if I'm wrong at a certain place.

Greetings
Dirk