On Sat, 2004-01-31 at 04:46, Mathias Fr�hlich wrote: > On Samstag, 31. Januar 2004 12:46, Christian Mayer wrote: > > Jon Berndt schrieb: > > > I just discovered that our property "metrics/eyepoint-x-ft" shows that it > > > is expected to be in units of feet. However, it is specified in inches in > > > our config file (in structural frame), and the property is bound to the > > > GetXYZep() function, which reports the eyepoint in the same way it is > > > specified: units of inches, in structural frame. I suppose this ought to > > > be changed. > > > > If we'd use SI units everywhere we wouldn't have that prolem... > > (and if NASA would have consitently used SI they wouldn't have lost one > > Mars probe...) > I am also used to the SI system. > But all I have seen up to now in the area of physical aircraft models is given > in units of feet and such. So I think the FDM should be able to work using > this values. > > What I can think of is an extension to the property tree, either private to > JSBSim or better in Flightgear in general. > I would like to be able to tie a value with a given unit into the property > tree. Then there should automaticaly appear a set of values in the property > tree which represent this value in different units. > > There are many possible scenarios how this can happen. The most compatible one > will be to tie a value with unit into the property tree without the unit > extension in the name. Then there are automatically the usual unit values in > the tree. For example the angle of attack will be tied to the variable > 'alpha' with an angular unit originaly given in rad, but that alpha will not > appear as 'alpha' in the tree, but instead two variables appear. One > 'alpha-rad' and one 'alpha-deg'. The same can of course be done for unit > conversion from and to the SI system. > The other possibility, which is not that backward compatible, will be that > each value is represented by a whole directory. Inside this directory there > are then only unit names. For example the angle of attack will then be > accessible through alpha/deg or alpha/rad.
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. > > 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. > > If someone has spare time to work on such a automatic unit system ... > Also, I have not looked into the property tree implementation if this could be > done easily. > > Greetings > > Mathias -- Tony Peden <[EMAIL PROTECTED]> _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
