# Re: Circular paths

From: Dirk Schulze <vbs85@gmx.de>
Date: Tue, 4 Jan 2011 13:51:25 +0100
Cc: <www-svg@w3.org>
Message-Id: <1CFE93D4-6877-46CA-BC01-F0D60BE636F3@gmx.de>
To: "ddailey" <ddailey@zoominternet.net>
```
Am 03.01.2011 um 23:42 schrieb ddailey:

> In the following:
>
> <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
```
Received on Tuesday, 4 January 2011 13:13:53 UTC

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