Hello,

I'm trying to make sense of covariance data I have in many files recorded using the GlobalSat BU353-S4 SiRF Star IV USB GPS Receiver mounted on a robot.

All of the covariance type values are 1, so I'm assuming that the covariance values were calculated from DOP values read from the receiver. I have covariance values in the covariance 0, 4, and 8 columns. Am I correct in assuming that these represent the +/- in the lat, long, and altitude values, respectively?

Are these values in metres or m^2?

If this is the case, where can I find/reference the algorithm used to get the covariance values?

If this is not the case, how are the covariance values generated? Is there a way to obtain more accurate lat/long using these covariance values, or will they only provide me with the error?

Thanks in advance.

# Position covariance [m^2] defined relative to a tangential plane
# through the reported position. The components are East, North, and
# Up (ENU), in row-major order.

# If the covariance of the fix is known, fill it in completely. If the
# GPS receiver provides the variance of each measurement, put them
# along the diagonal. If only Dilution of Precision is available,
# estimate an approximate covariance from that.