On Fri, 2002-03-15 at 13:03, Andy Ross wrote: > Jon S. Berndt wrote: > > Andy Ross wrote: > > > Ski jumps are an immediate counter example. > > > > Modeling ski jumps are the one example I can think of - the single > > special case - where this is important. [How many terrain polygons > > will it take to accurately model a ski jump, anyhow?] I'm not sure I > > want to do a complicated gear model with fidelity solely for this > > case. > > I think you misunderstand. The FDM's gear model is simpler in this > case. You give the scenery the position of the gear min/max > comprssion points, and it tells you where the tip really is. There's > less work to do in the gear model, not more.
That is, IMO, precisely the job of the gear model. Only the gear model can and should "know" the path that the wheel follows as it compresses. I'll certainly agree that right now it's not necessary to model anything more than compression along a straight line, but we know that's not real in alot of cases and should allow for it in the design of the FG-FDM interface. > > And think carefully about the simplification you propose. Yes, it > works in most case. But the existing code already works in most cases > -- all of the situations where we can get away with a simplified > per-gear model are *also* fine with the existing code. There's no > point to doing the per-gear stuff if we're not going to see any > benefit. A significant benefit will be had immediately -- the aircraft will follow the terrain while taxiing and the 3D model will look better. > > > Among the problems we run into with any proposed "right" approach, is > > that the aircraft may straddle polygons and the movement from one > > polygon to the next may result in discontinuous jumps with the surface > > normal. I think there needs to be some smoothing there. > > No need; that's what the integration algorithm is for. Even if the > underlying implementation was smooth (a spline, say), you're only > sampling it at discreet points anyway. You couldn't tell the > difference, so long as the difference across two samples was small. > > For the specific case of a ski jump: the speed of an aircraft when it > hits the jump is about 30 m/s. At a 120 Hz integration rate, that's a > per-sample change of 25cm, so our geometry needs to be 25cm long. A > ski jump is about 10m long, and is axially symmetric, so that comes > out by my reconning to 40 quads (or 80 triangles) for the deck. Not > bad at all; and the non-deck parts can of course be done at much lower > resolution. > > Andy > > -- > Andrew J. Ross NextBus Information Systems > Senior Software Engineer Emeryville, CA > [EMAIL PROTECTED] http://www.nextbus.com > "Men go crazy in conflagrations. They only get better one by one." > - Sting (misquoted) > > > _______________________________________________ > Flightgear-devel mailing list > [EMAIL PROTECTED] > http://mail.flightgear.org/mailman/listinfo/flightgear-devel -- Tony Peden [EMAIL PROTECTED] We all know Linux is great ... it does infinite loops in 5 seconds. -- attributed to Linus Torvalds _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
