> On Aug 29, 2016, at 7:27 AM, Loui Chang <louipc....@gmail.com> wrote: > > On Sun 28 Aug 2016 12:17 -0700, Nathan McCorkle wrote: >> "BRL-CAD users can accurately model objects on scales ranging from the >> subatomic through the galactic and get "all the details, all the >> time." > > Sounds like hyperbole to me.
There certainly is a bit there, and the statement should be caveated as being “within the limits of floating point". That said, it should be possible to accurately model through those scales but it doesn’t mean it will by default — tolerances have to be adjusted and some features become unavailable below certain thresholds without recompilation. >> In the freenode #brlcad IRC chatroom, recently the user 'brlcad' >> mentioned to me not to use a dimension of less than 0.005 mm, for >> reasons of 'computational stability' or some similar verbiage. >> >> I am working on MEMS devices which have nanoscale through macroscale >> features... 5 microns is HUGE for some of the things I will be doing. > > I would trust user brlcad's advice here, but am a bit surprised. In precision > machining .0001 of an inch or .001 millimeter are used as a 'general' level of > precision and can easily become more precise. I would have hoped brlcad could > handle nanoscale without issue! BRL-CAD's distance tolerance is adjustable and is 0.0005 by default, which is normally applied as a millimeter distance or default calculation tolerance. That’s 500 nm, so I would expect needing to adjust that down to at least 0.0000005 to get effective nm modeling (tol abs 0.0000005). That is nominally below single-precision floating point, so that begs for 64-bit too. That all said, another practical approach that would probably work even better would be to simply scale everything up by a factor. Modeling with a factor of 1000000 would make the default mm == nm. If I wanted to make something 1m long, I’d specify 1e^9 instead of 1000. If I wanted something a half-nm, it’d be 0.5, etc. Doing this would avoid needing to adjust tolerances. Cheers! Sean ------------------------------------------------------------------------------ _______________________________________________ BRL-CAD Users mailing list brlcad-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/brlcad-users
