On Sat, 2004-01-31 at 08:48, Mathias Fr�hlich wrote: > On Samstag, 31. Januar 2004 16:41, Tony Peden wrote: > > I certainly do agree that selectable units would be nice to have, but it > > would double the property tree memory requirements (since each property > > would then have to have a units property associated with it. In > > addition, such a system would significantly increase the amount of code > > that would execute at each property access. > Yes, this would increase memory requirements. I don't know the property tree > code well enough to judge about how much this will increase the memory and > execution time usage. > > Just for curiosity, how much memory usage does a single node in the property > tree have? > Or, do you know how much the usage of the property tree is compared to the > scene graph and the textures? > > > > This will also simplify building aerodynamic coeficient lookup talbes > > > which are sometimes given in, say 'lift per degree elevator deflection' > > > or, for an other aircraft type in 'lift per rad elevator deflection'. > > > I know, this is simple scaling, but I think that simple things should be > > > left to a computer ... > > > > > > :) > > > > All coefficients must be in consistent units (generally those of force) > > after the multipliers are applied, so I see no advantage here. There > > is no formal requirement for this since JSBSim does not attempt to > > assure unit consistency but it's there nevertheless. > The advantage would be, in my example, that I have the angle of attack/surface > deflections available in rad but the tables I have found for an f-18, I am > currently modelling, contain tables for the coeficients in something per deg. > So I have to scale this tables by hand/matlab/octave.
Yes, and I think that is appropriate for JSBSim. It would be more appropriate to put that kind of functionality into, say, an app that assists in creating a JSBSim config file. From that point of view, it is probably best to pick one consistent set of units and stick with them, which is what we have done. > > For a more general case, if one has all those aerodynamic tables given in the > SI system (are there any aircraft models in the SI system?), one will be able > to take these tables and simply use the input values in the matching units. So, for best performance, we are right back to the situation we have now. The only advantage (and being American I'm not sure it is one) is that we've switched to SI as the default. > > I, for my stuff, can work around, but it would be neat to have. > May be it is not worth the effort ... > > Greetings > > Mathias -- Tony Peden <[EMAIL PROTECTED]> _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
