On mercredi 17 décembre 2008, John Denker wrote: > On 12/17/2008 12:33 AM, James Turner wrote: > > On 17 Dec 2008, at 01:03, Melchior Franz wrote: > >> + var KT2MPS = 0.5144444444; # knots to m/s > >> + var MPS2KT = 1 / KT2MPS; > >> + > >> var LB2KG = 0.45359237; # pounds to kilogram > >> var KG2LB = 1 / LB2KG; > > > > Personally I think all these constants would be easier to read if they > > were written the same way as the Simgear ones, i.e MPS_TO_KT, NM_TO_M > > and so on. I understand the logic behind using '2' but it makes the > > identifiers rather dense. > > The tradition in the scientific community in recent decades > has been to do neither of the above. The best current > practice is called "unit analysis" or the "factor label > method". > > The essential idea is to consider _units_ as first-class > algebraically-meaningful objects. > > Here are some examples: Given any self-consistent set of > base units (usually SI but not necessarily) we can write: > inch = .0245 * meter; > foot = 12 * inch; > mile = 5280 * foot; > furlong = (1/8) * mile; > minute = 60 * second; > hour = 60 * minute; > day = 24 * hour; > fortnight = 14 * day; > > Then, given that set of units, if you want to express (say) a > velocity that was measured in units of furlongs per fortnight, > you just say so: > v = 1.2345 * furlong / fortnight; [1] > > Equation [1] converts _from_ arbitrary units _to_ base units. > If you want to convert the other way around, you use the > reciprocals of the units. > > The advantages in terms of concision, precision, and clarity > are rather dramatic. > > In this system, you don't need a conversion factor such as > furlong_per_fortnight_2_meter_per_second ... the question > just never comes up, because there are easier ways to do > what needs to be done.
BTW: there is a nice stand alone tool that i am using. http://convertall.bellz.org/ You may notice the units.dat file which is using that "scientific" notation Cheers -- Gérard http://pagesperso-orange.fr/GRTux/ J'ai décidé d'être heureux parce que c'est bon pour la santé. Voltaire ------------------------------------------------------------------------------ SF.Net email is Sponsored by MIX09, March 18-20, 2009 in Las Vegas, Nevada. The future of the web can't happen without you. Join us at MIX09 to help pave the way to the Next Web now. Learn more and register at http://ad.doubleclick.net/clk;208669438;13503038;i?http://2009.visitmix.com/ _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
