On 2/6/2011 10:24 AM, Peter Clifton wrote:
On Sun, 2011-02-06 at 10:55 +0100, Bert Timmerman wrote:One of Tom's "issues" that is to be kept in pcb are most of the mil grids because of the bazillion perf board and mil based parts on the market, to be bought for cheap by hobby-ists, or for "Quick-and-Neat" proto boards (we don't play or do dirty ;-). Just my opinion on the subject.Imperial parts are not a problem for a sufficiently fine metric grid. I don't think we should remove the option of working on a Mil grid though. I do it most of the time, even though I realise it is a habit best got out of.
I don't think you understand the intent. I don't think anyone is suggesting any changes to what a user sees. The issue is what base units are used internally and in libraries. By using metric values, imperial (is that really the right term?) measures (aka inches and mils) can be represented and calculated with no loss of precision. However, when inch type units are used as the fundamental measurement, it can be harder to get adequate precision to represent metric units.
1 inch = 25.4 mm... exactly 100 mm = 3.937007874016... sort of.In reality if you use enough precision in the base units you can always get "close enough" which is what engineering is about. But some folks have an issue with not working in the "best" possible manner.
I'm not sure this is really an issue. There would be significant pain making the change now. If the change is to be made at a later time, will it really be any more painful? So if there is no significant reason to switch and the pain does not increase if delayed... why bother with it now...?
Way forward: Metric "nm" grid internally, parts defined in whatever units the vendor's controlling dimensions are in. This might require relative origins to be used between the part design coordinate and the board's snap-grid, but that seems to be mandated by various IPC standards anyway.
Parts should match the rest of a system I think. The dimensions of a part can be stored in the units that best suit the system. It seems silly to store a part as metric and let the system round it off to inches on the fly rather than to do the round off when the part is created. But that's just my opinion.
Rick _______________________________________________ geda-user mailing list geda-user@xxxxxxxxxxxxxx http://www.seul.org/cgi-bin/mailman/listinfo/geda-user