Re: gEDA-user: coordinate systems [was: pcb crooked traces]

[Armin Faltl <armin.faltl@xxxxxx>]

Andrew Poelstra wrote:
> On Tue, Oct 12, 2010 at 10:12:41PM +0200, Armin Faltl wrote:
>   
> > Btw. while being a different topic, how about getting rid of the lefthanded
> > coordinate system, when all numeric computations have to be checked
> > anyway? This should make the cs consistent with trigonometric functions.
> >
> >     
>
> What does "lefthanded coordinate system" mean?
>   
It means, that positive coordinate axes can be generated as follows:
looking from Z+ to the center X+ moves into Y+ by a clockwise
rotation (for lefthand). Z+ is your extended thumb, then form your 
fingers to a hook;
the finger tips point into the direction of rotation around the thumb.
With cyclic permutation look along:
   Z+: X -> Y
   X+: Y -> Z
   Y+: Z -> X
A lefthanded coordnate system is the mirror image of a righthanded one,
the later being the norm for mathematical formulations, esp. vector
notation of rotation.
E.g. in polar coordinates P = P(r, phi) the angle phi has to be measured
counterclockwise from the X-axis to make the transformation to
cartesian coordinates look like:
   P = P(x, y) = P(r*cos(phi), r*sin(phi))
with X+ pointing right an Y+ pointing up (and Z+ pointing out of screen).

This is a convention. One can argue, to define the the sense of rotation 
clockwise
and have Y+ look downward, but this is against the mathematical standard
and pcb is the only CAD program I know of, that does like this.
It's incompatible with any CAM file format, plotter language, OpenGL etc.
Many raster devices and -image formats are lefthanded, probably the
reason, why pcb is.

Sorry for (partly) repeating myself.



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