# ISSUE-2241 (More explanations about the used coordinate system): 1. Introduction - More explanations about the used coordinate system [Module: Transforms]

From: SVG Working Group Issue Tracker <sysbot+tracker@w3.org>
Date: Sun, 22 Mar 2009 19:46:47 -0400 (EDT)

Message-Id: <20090322234647.BB9684DD60@crusher.w3.org>
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ISSUE-2241 (More explanations about the used coordinate system): 1. Introduction - More explanations about the used coordinate system [Module: Transforms]

http://www.w3.org/Graphics/SVG/WG/track/issues/2241

Raised by: Anthony Grasso
On product: Module: Transforms

I assume x, y, d in [x y d] are scalars (coordinates)
representing a vector (what is an object with direction and
length (euclidian) - is this correct?

How are the matrix elements in the projection matrix related
to the vector and the user coordinate system?

I assume, that the <px>, <py> and <pd> of 2.2 property
are related to the vector [x y d] - correct?
If so, what happens with pd = d = 0 with the matrix element
noted to be '1/-d'?

Similar question, how is the matrix related to user coordinate,
respectively how transforms a vector in the user coordinate system
with this matrix? (could be similar explained as done in the
SVG specifications)

It is noted, that [a b c d e f g h i j k m] is a vector -
what is the meaning of direction and the length (euclidian)
for this vector? If it has no meaning, it is maybe more a list
of scalars?

Is the d matrix element here related to that with the same
name in the projection matrix? I assume not, if this is true,
maybe the name for the scalar in the projection matrix should
be changed to another unused letter to avoid confusion.

I think, it would be simpler to reuse the 'a b c d e f g h i j k m'
from 1.2 in the matrices provided here, if it is a simple scalar.
If these are more complex terms write something like cos(alpha) is ok,
but it should be noted, what alpha is (an angle in degree I assume as
usual in SVG).
Note that the 'a' symbol appears with different meanings in section
1.2 - first as a matrix element, then as an (undefined) angle, as
I assume from the position within the cos - to avoid confusion the
angle should be replaced with another symbol, for example a greek
letter.

In 1.2.3. it is not obvious, what nx, ny, nz or something like
't.nx.nx' might be - is '.' here a symbol for multiplication or some
DOM/ecma-script-style notation separator or something else?
I assume multiplication, because I know those formulars already,
but I think this is not obvious for every reader.
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Received on Sunday, 22 March 2009 23:46:57 UTC

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