A question regarding XPlane 10

[MatthewS 761]

maybe I'm missing a point here, but why care so much about the flight characteristics of the AI aircraft around me? I could care less!!!!! As long as the AI world is there around me and I can see them, my TCAS can see them, ATC directs them, and they follow the ATC commands and SID/STAR rules,

I think its Austin that's missing the point. Seem's like he couldn't care less about having AI like in FSX and hence the 20 aircraft limit. Big mistake IMHO. If he added the ability for 100's of aircraft with simple flight models and then a sliding scale of max 20 full flight model AI/MP aircraft (the 20 nearest your aircraft) then we could have the best of both worlds!With regard to SID/STARS and complex ATC I think that's going to be the realm of 3rd party developers using the plugin SDK. Think of RADAR CONTACT but for XP10 where by it completely replaces the default XP10 ATC with a sophisticated ATC simulation including directing AI aircraft to use SIDs/STARs. Amazing!If XP10 has a flexible enough plugin SDK then this should be possible, assuming the ridiculous 20 aircraft limit is complimented with a "simple flight model" system for 100's of AI aircraft as described above.

[bsupnik 23]

Hi Guys,I will have to write a blog post to go into this in more detail later, but I think a lot of what has been written here is wrong. Y'all started under the assumptions that:1. The flight model is going to be too expensive to run on AI planes and2. A table based flight model would be faster.Those are both questionable assumptions at best...pretty much everything you can conclude from that is, IMO, dubious.(I should mention at this point that I am unaware of _any_ "dumbing down" features in the FM right now. My understanding is that we will pre-process control inputs in a number of ways, and the frequency of the FM can be set to multiples of the framerate, but even at the lowest setting, we do a full physics integration and the plane is the sum of the physics that are applied to it. I mention this now because I am about to speculate on some optimizations that _could_ dumb down the physics model, and I want to make clear that shipping X-Plane 9 does not do this!!)Here's the short version:The most expensive part of the flight model is ground interaction - that is, the flight model doing collision checking with the ground and various parts of the airplane. When an airplane is "clearly in the air" (e.g. an initial test shows it has high altitude) the FM isn't very expensive; when it is near the ground, CPU time cranks up as we make sure to get the touch-down characteristics just right; same with taxiing.So if we want to make the FM faster, there's really only one place to attack: ground interactions - it's the lions share of CPU time. There are a number of simple things we could do to improve ground interaction. For example, we could stop checking for body scrapes - since X-Plane has to handle physics correctly even if the user lands gear up and scrapes an engine, the sim normally tests the full geometry of the plane against the ground (which is not flat, even at an airport) - that adds up. If we are willing to trust that the AI planes don't screw up a landing* we could cut down ground check to only real landing gear, which would improve performance.Now what if we did some kind of 'lo-fi' AI, whether it's table based or it simply says "move the plane forward by this much" (E.g. a sort of track-based system)? If we want the airplanes to 'sit' properly on the non-flat airport surfaces, we _still_ need to do the most expensive part of the FM - the wheel-ground collision checks. So the total savings of a 'lo-fi' AI flight model would be very small, because at best we might partly improve the performance of code that doesn't have much impact on the sim.(To understand why you can only boost performance by attacking the biggest pigs, see here: http://hacksoflife.blogspot.com/2010/11/is-1-lot.html for gory details.)However, there would be a pretty huge cost to a lo-fi flight model: we would have to code a SECOND implementation of pretty much everything we already do in the real flight model! We would have to have new flight model files to support this new alternate flight model. The opportunity cost here is in developer time...the time spent building a separate flight model could have been spent performance-tuning the real flight model...even if we had a second flight model, performance tuning time would now be divided between the two flight models, and neither would reach its optimal performance.Besides my explanation above of why a lo-fi flight model wouldn't really be a win, two more comments:In software development, it often pays to try the simplest thing first, see how it works, and go from there, rather than _speculate_ how a system may perform and write a ton of code up front before you have real data. This is what we are doing...the simplest thing we can do is to run the real FM on the AI planes, and so far it looks like it's going to work reasonably. IF we hit data that says "no we have to do something radical", then we will...when the data says so, and no sooner. So far indications are that the real FM is going to be fine, and this makes sense from what we know about its performance characteristics. We also know that we have a lot of tricks we could pull to make the real FM faster for AI planes (e.g. removing engine scrape-checks, per above) before we have to go and write a whole new FM.And finally, dude, the real FM _looks good_. With the real FM, the AI planes move the way big heavy airplanes should move. They track the ground perfectly. If the ground has a bump and the airplane's suspension is loose, it sways like it should. The control surfaces deploy with their real time. When you're at an airport performing ground ops, you can get really close to the AI planes, and at that point these things matter! I speculate: once you take follow an AI plane running the real FM on the ground, it'll be hard to go back to a 'synthetic' FM.cheersBen* This may not be a safe assumption...what if a microburst hits an AI plane?

[MatthewS 761]

Yes real FM sounds great BUT... in practice how many AI planes is that going to allow?Lets assume that the plug-in SDK is flexible enough to allow a 3rd party dev to create a realistic ATC/AI simulation comprising:-1) Turn off the default XP10 ATC2) Implement realistic ground, clearance, departure, arrival, enroute ATC (think RADAR CONTACT for FS9)3) Implement real world flight schedules using the World Of AI (WOAI) schedules (controlled by the plug-in) and AI models (converted to XP format)4) Implement SID/STARs (ie AI aircraft actually follow correct departure/arrival procedures)Now imagine your at any big international airport, EGLL, YSSS, KJFK, WSSS etc. You going to see dozens of aircraft on the ground waiting at gates, about 10 aircraft taxiing in or out, maybe 1 or 2 actually on their takeoff or landing rolls, and probably another 30 aircraft within a 50nm radius flying the appropriate SID or STAR based on active runway.All this activity is being tracked/controlled by the 3rd party plug-in. It's setting way-points (lat/lon/alt/spd/rate of climb/decent) for the AI planes and letting XP10 actually 'fly' the aircraft appropriately using the flight model. BUT if XP10 only lets a max of 20 aircraft then the whole scenario described above wont work, instead every international airport will be almost dead!You've probably never seen or used FSX loaded fully with WOAI at a big airport, the immersion created by all the activity is outstanding. For XP10 to never be able to accomplish the same thing due to the 20 aircraft limit is a great loss of potential.Isn't there someway you can up the limit to say 200 aircraft whilst still maintaining high fps? Giving nearby aircraft a "hi-fi" flight model (ie this is what the user will see) and aircraft that are further away a very low-fps flight model. With aircraft far away its basically only the nav lights (especially at dusk/night) and TCAS "shadow" that are visible, so no ones going to actually notice the "lo-fi" flight model.edit: Of course you could let the user specify the ratio of 'hi-fi' to 'lo-fi' FM for AI aircraft, so they can scale as hardware permits.edit2: Understand what you say about not wanting 2 implementations of the FM but for XP to support say 200 aircraft then something has to give? But I guess what you're saying is NO there will never be any more than 20 AI aircraft, which is why you insist that a "lo-fi" model is not needed. Hypothetically if XP10 was to support 200 AI aircraft then surely you would have to consider some "lo-fi" model. When I say "lo-fi" maybe its still the same FM code as the "hi-fi" model but with various compute expensive bits turned off. Maybe you only do ground collision detection every 10 frames instead of every single frame? Tweaks like that to make it "lo-fi" and thus support 200 AI aircraft.edit3: Also, surely AI aircraft sitting stationary at the gate would have their FM turned off? So a busy airport populated with 100 parked aircraft is not consuming any FPS due to FM calcs. Can't you entertain the idea of more than 20 aircraft? You guys are really smart/experienced and surely you can work out a solution that lets XP10 have hi-fi flight model where it counts and still have 200 AI aircraft... IMHO you should be trying to make XP10 raise the bar and far exceed whats possible in FSX/Flight.

[bsupnik 23]

edit2: Understand what you say about not wanting 2 implementations of the FM but for XP to support say 200 aircraft then something has to give? But I guess what you're saying is NO there will never be any more than 20 AI aircraft, which is why you insist that a "lo-fi" model is not needed. Hypothetically if XP10 was to support 200 AI aircraft then surely you would have to consider some "lo-fi" model. When I say "lo-fi" maybe its still the same FM code as the "hi-fi" model but with various compute expensive bits turned off. Maybe you only do ground collision detection every 10 frames instead of every single frame? Tweaks like that to make it "lo-fi" and thus support 200 AI aircraft.

That is not at all what I am saying. I will comment on 20 airplanes tomorrow in a blog post, I don't have time to write it up right now.My point was only that:- we don't need to invent a second flight model.- using the real flight model doesn't mean we can't optimize./ben

[Guest veeray]

Ben: Also I don't think MS uses tables to begin with for ATC/AI aircraft... like you mentioned it seems to be tracked/rails and I believe that's because the ATC system only has control over the 6 variables plus groundspeed.

[Kesomir 0]

Personally I'd rather have the full flight model system with optimisations and grow the number of aircraft over time than something like MSFS handling.That said, It's probably better to actually see it implemented instead of guessing what it will look like.

[boshar 6]

I never understood the fascination some people have with AI planes. For me it's the thing I immediately turn of to get a better frame rate in FS9 and FS-X.As some have commented the FS AI looks like its on rials and on close inspection the AI planes do strange things. For the few times I need a crowded sky I would like an AI system that hooks into the real world flight tracking flight radar systems like this site http://www.flightradar24.com Maybe its even better to have a dedicated service log all that info so you can pick a date and time and have perfect AI traffic all the time. (some generated GA traffic would be needed but most AI fans seem to like the heavies anyway)