EPE is Estimated Positional Error (horizontal)


EPE = HDOP * URA (1-sigma) would give a measure of the 68% confidence circle, i.e., 68% of your position fixes would fall within and 32% would fall outside.

EPE = HDOP * URA (1-sigma) * 2 gives a measure of the 95% confidence circle, i.e., 95% of your position fixes would fall within and 5% would fall outside.

EPE = HDOP * URA (1-sigma) * 0.73 gives a measure of the 50% confidence circle, i.e., 50% of your position fixes would fall within and 50% would fall outside. This is also known in the literature as CEP (Circular Error Probable).




Definitions:

• HDOP - Horizontal Dilution of Precision
• URA - User Range Accuracy is a quantity that is transmitted in the navigation message that is the predicted (not measured) statistical ranging accuracy. Since it is defined for SPS (Standard Positioning Service), it includes SA.