GPS is a position finding system, an IMU is a position keeping system. The
IMU adds pitch, roll, & heading. Attitude data can also be obtained from a
multi-antenna GPS carrier phase system but not with the same accuracy or
data rate.

GPS and inertial systems complement each other as the inertial system can
continue providing data during a GPS dropout while the GPS system keeps the
IMU accurate over long time periods. Inertial systems provide acurate
high-rate data over shorter time spans. The IMU effectively "smooths" the
GPS data. A GPS positioning plus an AHRS system makes it possible to use a
less accurate MEMS IMU.

It's the accurate high-rate vertical acceleration data that is useful for an
inertial variometer. Accurate heading data when combined with ground track,
ground speed and ture airspeed provides real time vector winds. These
systems are now being used in UAV's and as performance increases and prices
decreases, there is no doubt they will find their way into gliders.

Bill Daniels

"Paul Repacholi" wrote in message
...
"Bill Daniels" bildan@comcast-dot-net writes:

Yep, it's possible. Total energy variometry can be done entirely in
the inertial domain. It's rapidly becoming affordable with MEMS
Inertial Measurement Units. I-FOG gyros are better but more
expensive. The enormous demand for UAV autopilots is driving the
development of low cost ADAHRS units that would be suitable for the
purpose.

How does that compare with a full x,y,z,dx,dy,dz,t GPS solution?
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