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

[joe tarantino <joeft@xxxxxxxxxxxxx>]

   ...and pcb is the only CAD program I know of, that does like this
   I've run across other PC layout tools which do this.  Mechanical CAD
   tools usually have (by default) Y+ pointing up, but for some reason PC
   design tools occasionally have Y+ facing down.  I don't remember any of
   these tools justifying their (less common) choice of convention
   however. :)
   Joe T

   On Wed, Oct 13, 2010 at 3:35 AM, Armin Faltl <[1]armin.faltl@xxxxxx>
   wrote:

   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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References

   1. mailto:armin.faltl@xxxxxx
   2. mailto:geda-user@xxxxxxxxxxxxxx
   3. http://www.seul.org/cgi-bin/mailman/listinfo/geda-user


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