kicad-developers team mailing list archive

[Avishay Orpaz <avishorp@xxxxxxxxx>]

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 ‏<lotharyx@xxxxxxxxx>:

>
>
> On Nov 14, 2019, at 3:15 PM, Avishay Orpaz <avishorp@xxxxxxxxx> 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 <‪
> evan.shultz@xxxxxxxxx‬‏>:‬
>
>> 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 <stambaughw@xxxxxxxxx>
>> 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.
>>> >
>>> >
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>>> >
>>>
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>