You are right about the fact that when a specific direction is assumed, the arc is fully defined. However, as i demonstrated at the beginning of this thread, Kicad does bot adhere to direction.
Avishay בתאריך יום ה׳, 14 בנוב׳ 2019, 11:10 אחה״צ, מאת Brian <[email protected]>: > > > On Nov 14, 2019, at 3:15 PM, Avishay Orpaz <[email protected]> wrote: > > The problem is that the definition of an arc in the legacy file format is > ambiguous. > > > Note of geometric pedantry: > Defining an arc by center, start, end is not ambiguous. If you always > draw the arc according to increasing angle, the ambiguity is resolved by > the order in which the endpoints (or angles) are specified. E.g., > (center), 0°, 90° unambiguously defines a 90-degree arc through quadrant 1, > while (center), 90°, 0° defines a 270-degree arc through quadrants 2,3,4. > > Whether the legacy file format uses that rule or makes it clear in any > way, I don’t know. But if it were truly ambiguous, the format wouldn’t > work. > > A midpoint makes the arc over-constrained and introduces the potential for > a case where the arc descriptor is not self-consistent (e.g. one constraint > is not on the same arc). An arc specified by three constraints is always > possible to draw; one with four might be impossible. > > That said, it’s an academic argument since the new format is already > defined. > > -B > > A center point and two additional points (or angles) define two possible > arcs - one smaller than 180 degrees and one larger (or two equal, 180 > degree arcs). In order to distinguish between the two, additional > constraint is required. If I understand correctly, the constraint here is > that the arc is strictly smaller than 180 degrees. In the new file format, > a midpoint is specified, solving this ambiguity. > > Avishay > > בתאריך יום ג׳, 12 בנוב׳ 2019 ב-23:28 מאת Evan Shultz < > [email protected]>: > >> I've also found >> https://www.compuphase.com/electronics/LibraryFileFormats.pdf to be >> useful. >> >> On Mon, Nov 11, 2019 at 4:14 AM Wayne Stambaugh <[email protected]> >> wrote: >> >>> Take a look at the legacy footprint library file format documentation[1] >>> for help. You really should be supporting the new s-expression file >>> format. The legacy file format is deprecated and is read only. >>> >>> [1]: >>> http://bazaar.launchpad.net/~stambaughw/kicad/doc-read-only/download/head:/1115%4016bec504-3128-0410-b3e8-8e38c2123bca:trunk%252Fkicad-doc%252Fdoc%252Fhelp%252Ffile_formats%252Ffile_formats.pdf/file_formats.pdf >>> >>> On 11/11/2019 4:42 AM, Avishay Orpaz wrote: >>> > I'm writing a program the reads schematic library symbols, and I'm >>> > having hard time understanding how arcs are drawn. >>> > Taking, for example, the Antenna_Shield symbol from device.lib. This >>> > symbol contains two arcs: >>> > >>> > A -1 -73 32 -882 1242 0 1 0 N 0 -105 -20 -45 >>> > A 1 -73 32 -918 558 0 1 0 N 0 -105 20 -45 >>> > >>> > Both arcs start at approximately the same angle (-90 = 270 degrees) and >>> > end at two different angles - the first at 124 degrees, the second at >>> 56 >>> > degrees. When the symbol is drawn, the first arc is drone clockwise >>> > while the latter is drawn anti-clockwise. So, how is it possible to >>> > determine the direction of the arc? >>> > >>> > Avishay. >>> > >>> > >>> > _______________________________________________ >>> > Mailing list: https://launchpad.net/~kicad-developers >>> > Post to : [email protected] >>> > Unsubscribe : https://launchpad.net/~kicad-developers >>> > More help : https://help.launchpad.net/ListHelp >>> > >>> >>> _______________________________________________ >>> Mailing list: https://launchpad.net/~kicad-developers >>> Post to : [email protected] >>> Unsubscribe : https://launchpad.net/~kicad-developers >>> More help : https://help.launchpad.net/ListHelp >>> >> _______________________________________________ >> Mailing list: https://launchpad.net/~kicad-developers >> Post to : [email protected] >> Unsubscribe : https://launchpad.net/~kicad-developers >> More help : https://help.launchpad.net/ListHelp >> > _______________________________________________ > Mailing list: https://launchpad.net/~kicad-developers > Post to : [email protected] > Unsubscribe : https://launchpad.net/~kicad-developers > More help : https://help.launchpad.net/ListHelp > >
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