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Re: Interpreting the ARC command


On 11/14/19 5:20 PM, Kevin Cozens wrote:
It is always possible to draw with four contraints if you were to use center point, radius, start angle, end angle.

There are different sets of constraints from which to pick.  The set of four you described are indeed immune from self-inconsistency problems, but as such they don't answer the question of >180 or <180 sweep (unless again one uses an implicit constraint, e.g. always draw counterclockwise).

As I think about it, your suggested set is the minimal set, if one treats cartesian start/endpoints as two constraints each (i.e. start X, start Y, etc.).  I don't think there's a way to get away with fewer than five numbers, regardless of what those numbers represent.  I do remain convinced that no more than five are required to be unambiguous, alongside the "always travel CCW" rule (which one could call an externally-applied, or implicit, constraint).

As I was typing this, Avishay added:

> Kicad does not adhere to direction

Ah, I missed that nuance.  In that case yes, definitely there is ambiguity.  But I've never seen a symbol get drawn with a wrong arc, so how does it resolve the ambiguity?  Is it just dumb luck that I've never seen it happen?


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