Re: [PEDA] Viewing gerber files

[Abd ul-Rahman Lomax]

the ability to import gerber files is extremely useful, not just for checking the gerber.

as others have suggested, using Protel for checking gerber suffers from the problem that errors in intepreting the gerber standards may be duplicated in the import routines. They could *not* be considered to have been developed independently.

the Protel octagon problem stems from an ambiguity in the original RS-274 (or RS274X, perhaps) specification. An octagon is plotted as a polygon with 8 sides. What is rotation zero? Most of us would pick the wrong answer, i.e., a different answer than the people who dreamed up the gerber spec decided was right. This is because we think of an octagon as being unrotated when the flats are aligned with the x and y axes. However, the polygon command is a generic regular polygon, and the only reasonable way to define rotation zero in that case is with a vertex on one of the axes. I think it is the y-axis, but I'm not sure. You had to read the specification very, very carefully to get this right. It was later revised to make the matter a little more clear, but by then the damage had been done. Protel then faced the problem of whether or not to change it. If they changed it, existing designs might end up incorrect.

They did not do the right thing, I think; they should have, as soon as the problem was discovered, created, at least, a warning message whenever octagonal apertures were used. Perhaps a text file could have been written to the gerber plot set explicitly stating what interpretation was being used. In that case, it would have been okay to go ahead and correct the program. Instead, they did nothing, and this problem continues to bite users from time to time. I don't know how DXP deals with this, I suspect that it does nothing, but I'd love to be wrong.

Importing gerbers has two options: batch and single file import. Batch import brings the files back in to the presumed original layers used. There can be some problems with this, but for quick gerber viewing, this would be the choice. Single file import takes the file into the current active layer. This is extremely useful for exploding, for example, a polygon to primitives. I've used it to make assembly drawings, plotting the silkscreen text and bringing that back, merged with pads, to a mech layer.

Protel gerber import was designed to import its own gerber, it does not necessarily work with gerber from other CAD systems even though they are RS-274X compatible. However, it is usually possible to massage such gerber into a form that Protel can import; this can be very useful in CAD conversion.

As to CAMtastic, it was developed completely independently from Protel, so unless they have monkeyed with it since buying it to make it more "protel-compatible" -- which I doubt -- it would be fine for checking gerber.

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