Calculating Horizontal Accuracy from NMEA strings

All-

Is it possible to calculate in realtime the horizontal accuracy (+/-
meters) of GPS positions from the NMEA strings? If so, it there a
formula or any guidance online that will help me calculate this?

I'm helping to write an application that would require the horizontal
accuracy from a GPS reciever to be display on a GUI.

Thanks in advance.

 

Some Garmin receivers transmit the error estimate in a proprietary
NMEA sentence.

Estimated Error Information (PGRME):

$PGRME,<1>,M,<2>,M,<3>,M*hh<CR><LF>
<1> Estimated horizontal position error (HPE), 0.0 to 999.9 meters
<2> Estimated vertical position error (VPE), 0.0 to 999.9 meters
<3> Estimated position error (EPE), 0.0 to 999.9 meters

I've seen reference other NMEA sentences that might be helpful but I
have never seen them on consumer grade receivers.

--- CHAS

 

See: http://edu-observatory.org/gps/gps_accuracy.html