From: Dr. Olaf Hoffmann <Dr.O.Hoffmann@gmx.de>

Date: Sun, 11 Jun 2006 19:24:46 +0200

To: www-svg@w3.org

Message-Id: <200606111924.46245.Dr.O.Hoffmann@gmx.de>

Date: Sun, 11 Jun 2006 19:24:46 +0200

To: www-svg@w3.org

Message-Id: <200606111924.46245.Dr.O.Hoffmann@gmx.de>

Hello, as mentioned correctly in '8.4 Distance along a path' it requires some special formula to determine a distance along a path, especially if one needs this to perform a paced animation with animateMotion to get the absolute value of velocity constant. keypoints of animateMotion need a correct path length to produce something useful, too. Correct formulas are available for example at wikipedia (keyword: arc length). This requires a simple integration, not an even simpler summation. The formula given in the table in '16.2.6 Paced animation and complex types' is simpler and will not give a useful result in general if applied to a paced animateMotion or to keyPoints. For example if bezier curves are used, it requires an integration to get the correct distance along a path. If the path consists of subpaths, there should be one integration for each subpath. The distance between special points of the path or even outside the path is not very interesting for a paced animation or for keyPoints. Normally the distance along the path is longer than the shortest distance between two path points. Another problem is, that according to '8.3 Path data' only cubic and quadratic beziers can contain 'control points'. Therefore the table in '16.2.6 Paced animation and complex types' does not define any distance for other path definitions. For subpath definitions possible with SVG, formulas as mentioned by wikipedia should be alway applicable, because the arc length of SVG-paths will be always finite (this is often not the case for example for fractal arcs or ifs). Best wishesReceived on Sunday, 11 June 2006 17:25:19 GMT

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