At 06:09 PM 10/3/2010, you wrote:
Rick Collins wrote:Yes, what I see is what I get. And to see it, I have to read the source code of the CADAt 08:24 AM 10/3/2010, you wrote:Rick Collins wrote:I really have no idea how things work in the gEDA/PCB world. With FreePCB the library has a default orientation for parts and there is a centroid vector to allow the pin 1 orientation to be set compatibly with the Gerber files. If you use someone else's design you need to verify that their library parts were done correctly or you need to use the same footprints which are a part of the layout and so are available. There is no reason to screw up something as simple as this.How the Gerber file looks depends on the footprint definition. Once one knows *exactly*a) how the transformations workb) that all libraries/generators(/custom made footprints) conform to a sensible standard checking is as superfluous as with screw diameters and pitches and before that pointI don't believe it's simple enough.I really don't know what you are talking about. The footprint will show up on your layout in some orientation. That is the orientation it will have on the board in the Gerber files. How will the "transformations" affect that? What you see is what you get.system, unless it's stated somewhere more accessible - like in a standard ;-)
That's what you don't get. You don't need to know diddly about the CAD system. The CAD system will produce output files that match your layout as you have prepared it. If it does anything else, it is very broken. At most you might want to verify that the data in the XYRS file matches the Gerber files for a small number of representative parts. Why do you think you need to verify the results by reverse engineering the code??? That is the stuff I am talking about "over thinking the problem". All you need to do is look at the output.
E.g., where is the centroid of a 3-leged part? Is it: a) the center of the bounding box of the pads b) the center of the bounding box of the pad centers c) the center of gravity of the pad centers (each weight 1) d) the center of gravity of the pad areas e) (0, 0) in the footprint definition file (or a designated vector inthere) ... That's what I need to know, before I can trust libraries and an XYRS files. Tbh, I'm not particularely happy, that this seems to be handled by some black magic withing 'pcb' instead of the library definitions.
When you find out what PCB does, a through e, what will that tell you? If you don't know what the standard is, how will you know if your design is correct?
Rick
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