How to find reasonable values for NavSatFix position covariance?
I have a GPS sensor whose driver doesn't report any info on positioning accuracy. Basically, what we have is lon, lat, alt only.
Is there a way to make up reasonable values for the position covariance in order to feed the data into a Kalman filter? (I assume that robot_localization's EKF/UKF doesn't insert useful default values in case the covariance is reported all zero...)
I'd be interested in any insights, from ballpark estimates to calibration methods or anything else.