From: Tanguy Ortolo <tanguy+svg@ortolo.eu>

Date: Fri, 2 Mar 2012 20:21:19 +0100

To: www-svg@w3.org

Message-ID: <20120302192119.GA3901@ortolo.eu>

Date: Fri, 2 Mar 2012 20:21:19 +0100

To: www-svg@w3.org

Message-ID: <20120302192119.GA3901@ortolo.eu>

Hello, According to the current recommentation, transformations can only be defined with numbers. While this can seem a logical constraint since transformations are matrices, which are multiplicated with lenghts, the reality is a bit more subtle: [ x'] [ a c e ] [ x ] [ y'] = [ b d f ] ⋅ [ y ] [ 1 ] [ 0 0 1 ] [ 1 ] Here, x, y, x' and y' are homogeous to lengths, but because 1 is adimensional, not all coefficients of the transformation matrix are. Indeed, e and f are multiplicated with the adimensional number 1 to make lengths. Thus, e and f are homogeneous to lengths. These coefficients appear only in one simple transformation, the translation. This is quite intuitive since a translation is basically defined by a length vector. Now, when drawing lengths in a natural unit distinct from the pixel, it is very inconvenient to translate these units to pixels just for translations. So, do you think not that it would be appropriate to modify the recommendation to indicate that coefficients e and f for matrices, and tx and ty for translations, are lengths and not numbers? Regards, -- Tanguy OrtoloReceived on Friday, 2 March 2012 22:13:37 GMT

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