I put your suggestion to my gerber-speaking colleague and he says that it 
would be easy to hook up the RS-274X in the manner that you prescribe. His 
only negative comments were : 1) that the definition files might be 
different eg one user's definition of "complex-teardrop1" might conflict 
with another user's defintion and these shapes would have to be defined for 
each and every library component. 2) The "simple" shapes of round and 
rectangular are not good enough for many of the shapes that he has defined 
which are mixtures of polygons, lines and arcs as well as round and 
rectangular. 3) The DRC speed would inevitably suffer since pads become 
complex objects - when comparing two ordinary pads there is 1 calculation 
but comparing two complex objects would be n x m calculations where n and m 
are the number of primitives in the two pads. There would be equal 
implications in screen refresh time and some implications in file size.

There are tools which seem to offer all the required functionality while 
maintaining speed, so it's definitely not impossible to achieve...


>There is a certain simplicity to Protel's restriction of pad shapes to
>ovals and rectangles. Yes, I know there are also octagons, but octagons
>don't presently work correctly (due to incorrect Gerber definition, rotated
>22.5 degrees) and I advise avoiding their use unless you are prepared to
>deal with the complications.
>I would suggest the addition of a third "shape." This shape would actually
>be a set of user-definable shapes called "complex-n$", where n$ is an ASCII
>name limited to legal filename characters. It would be defined in an
>RS-274X gerber file, perhaps complex-n$.pad. For simplicity, the file might
>be limited to positive flashes and draws using only round or square
>apertures. The "center" of the aperture would be the gerber origin, which
>would also be the hole location, if any. When a PCB file is loaded, the
>complex apertures would be converted to marked primitives (pads and lines),
>as if these had been present in the footprint or as free primitives.
>Ideally, the complex "files" would become part of the database, so a full
>implementation would require deeper changes in database structure, but the
>only change required for a first-level implementation of this feature would
>be the addition of a legal pad name(s) -- according to the existence in a
>defined location of the corresponding definition files -- and an addition
>of conversion and deconversion routines in the load and save processes. A
>naming convention would distinguish, for deconversion, pads which are part
>of complex pads with a character or character combination prefix or suffix;
>the complex subpad primitives would have a name associating them with the
>base complex pad. These pads would not be written to the PCB file, only the
>base pad with the shapename "complex-n$" would be written, with its normal
>pad name which associates with the net list.
>Footprint primitives in contact with a pad carrying a net would be presumed
>to be part of a complex padshape if that pad has the shape name
>"complex-n$". These would be assigned, at load time, with the net of the
>pad with which they are in contact. If a conflict arises due to contact
>with two pad nets, this would cause a net assignment failure and would
>create a DRC error as at present.
>Of course, the change suggested in the above paragraph would accomplish
>much. Nevertheless, complex pad shapes could be flashed in RS-274X by using
>the macro process, so the gerber file would contain full padshape
>information and such padshapes could be reconstructed as complex pads upon
>gerber import.
>Abdulrahman Lomax
>Easthampton, Massachusetts USA

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