# ISSUE-2241: 1. Introduction - More explanations about the used coordinate system

## 1. Introduction - More explanations about the used coordinate system

State:
RAISED
Product:
Module: Transforms
Raised by:
Anthony Grasso
Opened on:
2009-03-22
Description:
http://lists.w3.org/Archives/Public/www-svg/2009Mar/0178.html

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.
Related Actions Items:
No related actions
Related emails:
1. minutes, 22 March 2012 SVG WG telcon (from cam@mcc.id.au on 2012-03-23)
2. ISSUE-2241 (More explanations about the used coordinate system): 1. Introduction - More explanations about the used coordinate system [Module: Transforms] (from sysbot+tracker@w3.org on 2009-03-22)