I have a marine navigation app which displays GPS quality information when receiving NMEA message from an external GPS. These include the number of satellites and Horizontal Dilution of Precision (HDOP).
As far as I can see, the only additional information available through location services (for devices with built in GPS) is horizontal and vertical accuracy.
Am I missing anything? Also does anyone know how horizontal accuracy is derived from HDOP?
@Baylward, you are correct. Locations we output may be a blend of multiple sources of information, so we use horizontal and vertical accuracy rather than HDOP or satellite count to represent estimated location errors.
The horizontalAccuracy field contains the estimated horizontal error statistics of the corresponding location. It should be interpreted as an estimated two-dimensional root mean square error, calculated from a scaled Chi distribution with two degrees of freedom. In other words, if sigma_e and sigma_n are the one-dimensional standard deviations of location errors in the east and north directions at the associated location, then horizontalAccuracy for that location will be reported as sqrt(sigma_e^2 + sigma_n^2). Valid values of horizontalAccuracy are 0 < horizontalAccuracy <= Inf. horizontalAccuracy == 0 specifies a perfectly-known location and is unexpected. Negative values indicate the associated location is invalid.