On Tue, 13 Jul 2004 09:49:19 -0500, Curtis wrote in message <[EMAIL PROTECTED]>:
> Mat Churchill wrote: > > I'm also assuming that there is currently no way of inputing pitch, > > roll& yaw data while playing back NMEA data ? if so would this be > > easy to implement? ..do keep these _separately_ from the gps data, say off a gyro platform. Accellerometers are optional, accelleration can be both measured and calculated off the gyro platform. Also, consider recording total and static pressures, AoA, and a compass, these are fairly easy to read and process. You'll need to pool your data anyway. ;-) > The NMEA format doesn't account for pitch/roll/yaw. I'm not sure we'd > want to start modifying the format either. Probably the nicest > solution (but would involve some effort) would be to write some > offline tool that would take the saved NMEA data (probably at 1hz?) > and do all the roll/pitch/yaw calculations and interpolate for 30 or > 60 hz. Then you could feed this back to FG as FGNativeFDM structures > and get nice smooth playback. (You could even feed FGNativeCtrls > structures back too and animate the control surfaces if you want to > estimate their positions.) ..by now we have gyro and IMU etc data format ideas? > > I found this paper on the web regarding generating accurate pitch, > > roll, yaw, altitude, position & velocity data. > > > > http://www.cmt-gmbh.de/crossbow_gpsdmu_german_gyrotech_paper.doc > > > > I think the end product derived from the above was this: > > > > http://www.xbow.com/Products/productsdetails.aspx?sid=104 > > > > There are other papers out there from people such as creators of > > robot football teams all tackling similar issues. > > > > I spent the weekend digging around on the web and made some calls on > > Monday and it appears the component cost could be as low as �300 - � > > 400 to make a flight logger. One particular solid state gyro is > > mentioned as cheap but good by everyone from amateur rocket clubs to > > R/C helicopter builders. ..how much can such ready-to-go flight loggers be sold for? ;-) > > However if you read the above document the real deal breaker re > > making a homemade flight logger is not the component cost, but the > > processing of the signal from the gyros into accurate attitude / > > position data. > > Yes that's hard ... I won't mention any names, but I've seen phd and > master's level people struggle significantly with implimenting kalman > filtering in a real world task. The theory itself is difficult > enough, but getting a correct implimentation in your own code seems to > be an order of magnitude harder. (Other's may disagree, I've never > attempted to understand/impliment kahlman filtering myself, so I'm not > speaking with much authority here ...) :-) > > > Someone more than at home with extended kalman filter formulae > > amongst other things needs to write an algorithm to process the turn > > rate & gps data into accurate attitude / position data. From what > > the paper says substantial testing would be required. This actually > > is rocket science ! and is way above my head ( at least 60 miles > > above my head ) > > > > I did think that at least with a flight logger rather than a real > > time device you could record raw turn rate / gps data in flight and > > do all the processing on your PC when you got home, not that that > > diminishes the complexity of maths that would need doing. > > If you want to just approximate roll/pitch/yaw based on gps data then > you could always start simple, use a simple smoothing function, and at > least get something working before you tackle more complex approaches. ..and all this will only be guesswork, as you _guess_ it from your gps data, rather than measure and record it. Adding heading data will help you get averaged wind, but not immediate stuff like turbulence jolts. > If you need to process raw gyro output (accelerations) and translate > those into accurate positions and orientations, then you probably need > to dig into Kahlman filtering. ..doing both _can_ give you the wind around your plane, _if_ you get Kalman etc right. ;-) > > From what I've observed on this list it would be no surprise if some > > of the readers do understand the principles of Kalman filters. Maybe > > some of the information is already being shared by amateur rocketry, > > R/C helicopter enthusiasts etc ? > > Aaron Kahn (I don't know if that is quite the right name) was a guy on > the autopilot.sf.net list. He is the only person I've ever seen > personally who's produced a successful kahlman filter implimentation > in real computer code to run in real time on a real embeded computer. > > I've seen a lot of people that can talk your ear off with the high > level theory, or who know some of the basics of what Kahlman filtering > does and what it's good for. But I've only seen one person who's > managed to pull off a real world successful implimentation ... :-) > > > It will take a while, but I am building a simple GPS logger at the > > moment. If anyone is interested in taking part in getting the gyro > > part to work I could have it built here and post it out to others > > for testing. > > I'm interested ... along with 100 million other things ... but please > keep us up to date on your ideas, questions, and progress. ..amen! ;-) Gps on serial wire into laptop, FG and Atlas or Kflog, gyro platform into usb hub or next serial wire, and paralell port or usb hub reading pressures? Plane can supply laptop power on those long hops, eh? -- ..med vennlig hilsen = with Kind Regards from Arnt... ;-) ...with a number of polar bear hunters in his ancestry... Scenarios always come in sets of three: best case, worst case, and just in case. _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
