kicad-developers team mailing list archive

[José Ignacio <jose.cyborg@xxxxxxxxx>]

Why not use start end, "bulge" as DXFs do for LWPOLYLINEs?
http://www.lee-mac.com/bulgeconversion.html Instead of the bulge number
(which is related to the included angle of the triangle formed between the
endpoints and the center) you could also write out the angle of the arc
directly. This is a very compact representation for polylines that have
arcs (like arc traces) as the center point is implied. there are also no
invalid values as a bulge of zero is a straight segment and an almost full
circle of infinite radius would be + or - infinity.

On Wed, Jul 10, 2019 at 6:57 PM Seth Hillbrand <seth@xxxxxxxxxxxxx> wrote:

> On 2019-07-10 14:08, Brian wrote:
> > On 7/10/19 2:02 PM, Seth Hillbrand wrote:
> >> Start-center-end is under constrained and requires the additional
> >> knowledge of which direction the arc is going.
> >
> > On the contrary.  Start-center-end is fully constrained.  Arc
> > direction is implied and unambiguous.
>
> Ah yes, you are right.  We can assume a CW or CCW direction and swap
> start/end to match.
>
> The only remaining concern would be robustness.  You can create a
> start-center-end combination that is invalid, so we'd need to define a
> governing parameter.
>
> The start-midpoint-end triplet can also be invalid but only if you
> assume the midpoint is exactly midway.  The three-point conversion I
> listed previously allows the third point to exist anywhere on the arc
> and avoids this issue.  We would use midpoint for convenience when
> writing the file but don't require it when reading.
>
> Is there a good solution to this issue for the center point idea?
>
> Best-
> Seth
>
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