On Mon, Oct 22, 2012 at 12:44 PM, László Monda <[email protected]> wrote: > Hi List, > > http://www.cadsoftusa.com/eagle-pcb-design-software/new-in-v6/ states > that "Work with flawless conversions between mm and inches through > increased internal resolution (allows grids of 1/4, 1/8, 1/16,1/32 and > 1/64 mil)". > > Doing a little math it turns out that: > > 1/4 mil = 0.006 35 mm > 1/8 mil = 0.003 175 mm > (1 nm = 0.000 001 mm) > 1/16 mil = 0.001 587 5 mm > 1/32 mil = 0.000 793 75 mm > 1/64 mil = 0.000 396 875 mm > (1 pm = 0.000 000 001 mm) > > This worries me because given the vast hobbyist userbase of Eagle it'd > be tremendously useful for KiCad to be able to import Eagle files > eventually *without* loosing any accuracy. According to the above > values KiCad will retain precision up to 1/8 mil but not below. > > I assume that nanometre resolution has been choosen because whoever > was in charge thought that it should be precise enough. It's surely > accurate enough to manufacture anything but conversion problems can > arise. I for one used KiCad from the pre-nanometre era and specified > values like 8.645 mm which got rounded to the closest available value. > You may say that it's not a big deal but it is very disturbing and > it's certainly not something that one expects from a CAD software. > > As absurd as it might seem only picometres would be small enough to > provide the needed resolution to not loose accuracy. > > Please let me know what you think. > > PS: By the way, just for historical reasons what was the resolution of > KiCad before the nanometre era? > > Thanks. >
I think the problem is not there in the real world. http://en.wikipedia.org/wiki/Gerber_format#RS-274X_extended_Gerber The output for production is at most accurate to a micro-meter or a micro-inch. Photo plotters and CNC drill machines are not as accurate in practice. Furthermore, footprints are mostly defined on a grid, which is of a known size (not in pico-meters accuracy but in milli-inch or micro-meter) >From the help-page of eagle ; real u2mic(int n); real u2mil(int n); EAGLE stores all coordinate and size values as int values with a resolution of 1/10000mm (0.1µ). The above unit conversion functions can be used to convert these internal units to the desired measurement units. For me personally the nano-meter is overkill already, more zero digits behind the comma than before, we now limit the total board size because of integer overflows. Hope this is useful for you. Have a good day, Edwin van den Oetelaar _______________________________________________ Mailing list: https://launchpad.net/~kicad-developers Post to : [email protected] Unsubscribe : https://launchpad.net/~kicad-developers More help : https://help.launchpad.net/ListHelp
