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

Date: Sun, 22 Mar 2009 20:40:59 +0100

To: www-svg@w3.org

Message-Id: <200903222040.59339.Dr.O.Hoffmann@gmx.de>

Date: Sun, 22 Mar 2009 20:40:59 +0100

To: www-svg@w3.org

Message-Id: <200903222040.59339.Dr.O.Hoffmann@gmx.de>

Hello SVG WG, just minor notes about http://www.w3.org/TR/2009/WD-SVG-Transforms-20090320/#_4x4-to-3x3-conversion It starts with: "A rectangle ABCD is given on plane X-Y. When a 3D affine transform and perspective projection are applied, a quadrangle A'B'C'D' will appear on the X-Y plane. Note the X-Y plane is the projection plane. Generally, this mapping is expressed as a 4x4 matrix." As far as I understand this, this rectangle ABCD in not used in the later part of the section. What is the purpose of 'ABCD'? For authors it should be sufficient, to explain, how a vector transforms and is projected, what is done with the point K. For an implementor it is maybe interesting to know, whether planes are projected to planes, lines or points; straight line are projected to straight lines or points and cubic curves are projected to other cubic curves, that only the points and control points have to be recalculated - or whether these are more complex computations. There are some expressions like "M = P.T" If '.' is meant here to be an operator for multiplication (Just guessing, I have never seen this before, typically something like * or · or something is used), this should be defined ;o) In PHP the '.' is used to join/jam strings together for example... Typos (?): "An affine 3D Transform Matrix T is given as M = ..." -> "An affine 3D Transform Matrix T is given as T = ..." ? "The combined matrix Mcan be expressed as ..." -> "The combined matrix M can be expressed as ..." ? "If matrix F can be used to map point K to point K' as shown below ..." I'm missing the 'then' case here or is it a typo? 'If' instead of 'The' or 'A'? "Therefore, the combination of An affine 3D Transform Matrix and a Perspective Projection Matrix" -> "Therefore, the combination of an affine 3D Transform Matrix and a Perspective Projection Matrix"? Best wishes OlafReceived on Sunday, 22 March 2009 19:43:52 UTC

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