# Re: [Flightgear-devel] Re: Real Flight PLayback ?

```Sorry for joining this thread lately...

As suggested by serveral people if only GPS data are available (ie:
Lat/Long, Ground Speed,  Ground Track and rough altitdue.)```
```
For pitch restitution :
With two dated altitude data, we can compute vertical speed.
>From vertical speed and ground speed, we can compute the Flight Path Angle.
For playback purpose we can assume the AOA is 0° and then have the pitch
angle equal to the
FPA (or estimate it as a linear function of ground speed - ie assuming the
wind is null... - )

For roll restitution :
With two dated track data, we can compute the track "time" derivate.
>From the track derivate and the ground speed, we can compute the bank angle
(assuming symetric flight)

It could be approximated to the ground track. (ie: assuming a null wind)

A couple years ago, I ran some simulations and it gave very nice results
even vith 1Hz GPS output data (and software smoothed to 25Hz for display
confort).

Acceleros and gyros MEMs are good short term, and for quick attitude
changes.
The here above Pitch, Roll and Heading attitude estimation stabilizes long
term the cheap MEMs IMU.

An other way to stabilize cheap MEMs gyros and acceleros for attitude
determination is to use 3D magnetic sensors : it's fully independant of the
vehicule acceleration *but* dependant of the magnetic field environement...

Olivier

PS : Mat, if you still need it, I have some C code which reads GPS data from
a RS232 - MNEA format, with a very low CPU usage; which let plenty of CPU to
run FGFS in parallel if you see where I'm heading ;-)

From: "Alex Perry" <[EMAIL PROTECTED]>
> While not strictly true, the assumption is close enough for playback.
> You can infer AOA from airspeed and add this to the flight path angle.
> Similarly, you can use airspeed and radius to infer roll angle.

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