Jon S Berndt wrote: > On Wed, 15 Dec 2004 18:22:30 -0000 > "Vivian Meazza" <[EMAIL PROTECTED]> wrote: > > > There are several points here. > > > > 1. The fact is that most 3d (I think all, but I haven't checked) > > rightly or wrongly already use normalized values. It would be a > > significant task to change. > > Agreed. This is a consideration. If the FDMs can divest themselves of > the need to provide normalized values, I don't care what is done on > the other side of FGInterface. > > > 2. I don't think we tell YASim the correct angles to use. Therefore > > the normalized output, factored to produce the correct visual angles, > > is the way to do it right now. > > How does YASim know how far an aileron can deflect? How does > FlightGear know how far to deflect the aileron? The FDM needs to know > and use control surface deflection in degrees (or radians) - > normalized values won't cut it for flight modeling. Since the FDM > knows "truth", it can be the one-stop supplier for this angle - rather > than normalizing it (based on what?) and shipping that to > FlightGear/SimGear where it must be told how to de-normalize the > normalized value for display.
Andy Ross will be able to explain this better than I, but my understanding is that YASim applies a proportion of the appropriate force. > > 3. For consistency, and remember that some 3d models are used with > > both YASim and other FDMs, we need normalized values. > > This is just plain wrong. If an aircraft can deflect the elevator +/- > 30 degrees that's the way it is. Regardless of FDM. We are talking > about absolutes, here, not some arbitrary limit decided upon by the > FDM. Even if the FDMs use different values for elevator deflection > limits, the aircraft would fly based on the deflection actually made, > and the 3D model will show what the FDM says it is flying to. Item #3 > here is a non-issue. I don't think so. YASim can only output a normalized value, since we don't tell it what the input angle is, although I'm not clear if we _can_. I don't think we want different interpretations for different FDMs, otherwise we will have to have different animations for different FDMs. My instinct tells me that YASim has it right here, because it is intended for aircraft > > 4. It doesn't matter where the conversion is done. If FG is the only > > user of normalized values, it makes sense to do it there. > > Yes, and that's my point. But there is a little more to it than that - > it's about accuracy. If the FDMs abandon the provision of normalized > values, what will FlightGear do with what is provided? If JSBSim sends > FlightGear a 20 degree elevator deflection, what does it normalize > that value based on? FlightGear will need to be provided with the > maximum travel for aerosurfaces. Since teh FDM will also work with > these maximums, this could introduce another "point of failure". If you don't want to do the conversion in the FDM, then you will need to pass max deflection to FG, otherwise leave it where it is. What about landing gear, arrester hooks etc. etc? It makes sense to me to use a single standard for all moving items which can be animated, but we can work around it. > > I have no doubt that this point was vigorously debated at some point > > in the past, and for good reasons we are where we are. We need to > > revisit those discussions and revalidate the decisions before making > > any change. > > I would think we would have discussed this in the past, but I don't > remember having done so. Normalized values were introduced in JSBSim > about 2 years and 9 months ago, according to our CVS logs. Perhaps some of our longer standing developers can shed some light on the background to this important decision. Regards, Vivian _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel 2f585eeea02e2c79d7b1d8c4963bae2d
