Jittery motion when writing Lat/Lon/Height to FS2004

[DrFrankencopter]

I've managed to build FSUIPC into a function that executes inside a Matlab/Simulink model to send real flight test data (specifically, differential GPS lat/lon/height plus attitude and heading) to FS2004. But, the motion that I see in FS2004 is very jittery. I have tried this in slew mode, and in normal mode, and the result is the same.

My guess is that FS2004 is attempting to run it's flight dynamics model in-between sample updates. Is there any way to turn off the flight model, and just directly drive the aircraft position?

Also, does FS2004 use the WGS-84 elipsoid for lon/lat data. I am sending very precisice positions (in WGS-84 coordinates), but the aircraft isn't drawn in exactly the right spot (could be innacuracies in the airport scenery model).

Thanks,

Kris

[Pete Dowson]

My guess is that FS2004 is attempting to run it's flight dynamics model in-between sample updates. Is there any way to turn off the flight model, and just directly drive the aircraft position?

That's exactly what slew mode is -- yet you say you've tried that with no difference. The other ways include pause mode and setting the simulation rate to zero.

I think the only way you will get it relatively smooth is to try to synchronize FS and your update rate. For instance, if your updates are regulated to 20 per second, set the frame rate limiter in FS to the same.

Also, does FS2004 use the WGS-84 elipsoid for lon/lat data. I am sending very precisice positions (in WGS-84 coordinates), but the aircraft isn't drawn in exactly the right spot (could be innacuracies in the airport scenery model).

No idea what coordinate system is used, but the best scenery uses satellite data to position things, so I guess the system is the same as whatever the satellite data is using. If you are talking about specific sceneries, then whose are you comparing it to? Most good add-on scenery is a lot more accurate than the defaults.

Regards,

Pete

[vdkeybus]

Also, does FS2004 use the WGS-84 elipsoid for lon/lat data

I think the scenery is based on it indeed. You could check this with the authors of NAV3, Courseplanner, FSNavigator, etc. I think some of them use other WGS-84 databases (than the FS2000 scenery, which is quite hard to decode) and still get quite accurate positionings.

I have tried this in slew mode, and in normal mode, and the result is the same.

I also noticed that, when slewing, the plane sort of 'flies' to the new location. Maybe you could try a totally different approach:

For large displacements, slew it. For small ones, write an 'autopilot' in Simulink which actually flies the aircraft through your LLA coordinates using FSUIPC. Frame rates and smoothness will be uncompromised. The additional benefit is that you get the pitch, bank and attitude (PBH) for free, something you didn't mention of having. And you will need a lot less updates because the plane will interpolate the track perfectly for you.

And you get sound as well :-).

It might require a modified flight model with increased 'engine power' and drag to allow the 'autopilot' to better follow the track.

Just a thought for those wanting to bypass the FS flight model.

J.

[DrFrankencopter]

Sounds like a little too much trouble....I'm going back to FlightGear, where I've already had good success in driving it with real flight data. Dealing with the FS format is a little too much overhead, and the performance is poor compared to FlightGear (where I'm getting as high as 100 frames/sec).

I was hoping that the user built airports in MS Flightsim would be sufficiently accurate for my needs, but that doesn't appear to be the case.

Oh well, thanks anyways.

Cheers,

Kris