GPS accuracy when sat on a window ledge, avg distance between fixes = 3.36m, max dist = 18m

All credit to Wouter Bulten for a light weight javascript kalman filter : https://github.com/wouterbulten/kalmanjs­

Included the library and :

var spdFilter = new KalmanFilter({R: 0.01, Q: 2});
var altFilter = new KalmanFilter({R: 0.01, Q: 2});

Use the two filters to smooth the speed and alt values of each successive fix :

// Smooth data

if ( lf.smoothed !== 1 ) {
  lf.speed = spdFilter.filter(lf.speed);
  lf.alt = altFilter.filter(lf.alt);
  lf.smoothed = 1;
}

I haven't tried it on the lat/lon position values as the app is not about position as such so would be interested in the results of that. Alt was varying by as much as 10-15 m when stationary but with this filtering is now stabilising within 1-2m of known altitude references. Good enough for what I need.