kicad-developers team mailing list archive

[Larry Doolittle <ldoolitt@xxxxxxxxxxxxxxx>]

Jon -

On Wed, Jul 10, 2019 at 01:29:11PM -0400, Jon Evans wrote:
> I am curious why start-midpoint-end is better than start-center-end, though.
> I think the latter is used more often in mcad tools, although I could be
> wrong.

start-center-end is mathematically over-constrained, so it sounds
worth avoiding.

start-midpoint-end encodes a useless -- but not over-constrining --
degree of freedom, in the position along the arc of the "midpoint".

The mathematically correct number of parameters is five, and Seth makes
a good case that four of them should be the start and end coordinates.
One non-pathological definition of the fifth parameter is curvature,
in units of inverse-distance.  Zero is no curvature -- converts back to
a straight line.  The sign of the curvature tells whether the arc bends
left or right.  I _don't_ assert that this is any better in real life than
start-midpoint-end.

  - Larry