On Fri, Oct 08, 2010 at 11:46:39AM +0200, Armin Faltl wrote: > Gabriel Paubert wrote: > >Really, the inch is by definition 2540µm, not the other way around > >since over 50 years ago. > As far as I know, 1" = 25400um, but I see your point ;-) > > The only practical consideration I see is, that the internal unit of PCB > allows handling with integer-arithmetic (makes comparisons a lot > faster and safer than floating point). > Assuming 32-bit signed numbers with 1/100mil this gives: > 254nm resolution and +-545.46m coordinate range > 32-bit signed and 1nm gives: > 1nm resolution ;-) and +-2.147m coordinate range > > I don't know, if pcb really uses fix-point arithmetics, but even if > not a reasonable internal unit has some importance. AFAIK with > floating point, the average internal number should be around 1. > > HTH, Armin >
I don't think we could reasonably use floating-point. There is no room for rounding error when designing tight areas of a PCB. As for board limitations, I think that if you are designing boards bigger than 2m (and cannot make a small board then scale the gerbers after-the-fact), chances are you've got a 64-bit system. Of course, then we need to worry about file-format compatibility between 32- and 64- bit systems... Suppose we stored a scaling factor in the .pcb files, of x10, x100, x254, etc? Then we could use nanometer precision by default and go bigger if we need a bigger board. Andrew _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user