On Fri, Oct 8, 2010 at 5:46 PM, Armin Faltl <[email protected]> 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 >
No floating point, all integer to avoid rounding errors. DJ, are the pcb units still wrapped in the accessor macros for converting between internal representation and real world values? If so... Guys change the converters and have at your hearts content. It should be a 2 hour patch. Now for conversion errors, are you really seeing errors in your metric PCBs? As far as I am concirned the internal unit is meaningless provided it is fine enough. I know no fab house that is going to have a tolerance as good as 254nm or .01mil So as far as it matters in the real world, getting other things done in pcb is much more important, than a conversion to metric base units. meaning proposing that we make PCB 64 bit and nanometers is redicolus. We will double our ram usage and not gain ANY benifits. And to think this started out cause I suggested to use a really corse grid to start layouts, and keep things pretty. Use metric if your primarally using metric parts and use mils if your using inch defined parts. Chances are that people arn't placing their parts by snapping to pin one to move it on grid when placing anyhow. BTW, I'd vote for 1 unit, and a scale value. That is if you are making a 10 meter antenna, Then you set the PCB's scale to 0.1mm. Steve _______________________________________________ geda-user mailing list [email protected] http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
