Phone with GPS and barometer - I want a Kalman filter

My personal elevation, and air pressure corrected for elevation both change rather slowly.

With a suitable Kalman filter, my phone should be able to use the barometer to cancel some of the GPS elevation noise. I don't know how much noise the barometer has, but it seems low, compared with pressure change when I walk up a hill.

Most important, I want the corrected elevation estimate used to compute my local sea level pressure.

The pressure curve doesn't tell much about the weather, when I suddenly walk home from the office.

Screenshot from Barometer Monitor.