Merge multiple GPS and IMU to get more accurate position and attitude

I have multiple GPS and IMU that are located at known positions of an aircraft. Is there a ready to use implementation to merge the data with for example a Kalman filter? Or any good hints to papers/tutorials? Thanks

[Rik]

I would be interested to copy your solution (from the FEX? hint, hint). I expect a standard Kalman implementation would require quite some editing to implement multiple sources and sorting them.

You could also approach this as a 4D curve fitting problem (lat,long,alt,time) and let Matlab do the heavy lifting instead of implementing a Kalman filter.