Mail Archives: geda-user/2016/01/09/14:45:36
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On Jan 9, 2016, at 2:29 PM, DJ Delorie <dj AT delorie DOT com> wrote:
>=20
>>> I cannot make sense of a board cutout as a layer. It=E2=80=99s an
>>> operation that applies to a set of layers.
>=20
> You're confusing drawing layers with physical layers. PCB's drawing
> layers are just collections of shapes, much like gschem's "schematics"
> are just pages of lines. How each layer is interpreted depends on
> what the people at the fab house are expecting. If you tell them "the
> shape in this gerber is for internal cutouts", that drawing layer then
> means "shapes for internal cutouts=E2=80=9D.
That seems to me to be a misuse of the word =E2=80=9Clayer=E2=80=9D.
layer |=CB=88l=C4=81=C9=99r|
noun
1 a sheet, quantity, or thickness of material, typically one of several, =
covering a surface or body.
You=E2=80=99re talking about operations applied to one or more layers.
>=20
>> Neither do I. The drawn shape is either a positive image or a cutout.
>=20
> It's just a shape. Interpreting it is up to the humans who talk to
> each other about what the shapes mean. It would be nice if there were
> automatic ways of conveying this information (perhaps STEP) but at the
> moment we're relying on good old "talking" to solve that problem.
>=20
>> Gerber file format have the concept of dark and clear polarity.
>=20
> Irrelevent here, though. And I've seen way too many fabs get this
> wrong; pcb never takes advantage of this.
>=20
John Doty Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd AT noqsi DOT com
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