NMEA Manual based on MediaTek chipset - Manual
FTX-HW-13002-A
Preliminary
Page 32 of 39
5
FIX Valid Flag
This chapter concerns only the UP500 antenna module.
It is important to note that the current UP500 receiver firmware output position coordinates in RMC and GGA
messages even if the position is flagged as invalid in the NMEA RMC message.
This is contrary to most other GPS receivers, and the consequence is that a trace displayed on a map might look
inaccurate. The advantage for some applications is that you do get some kind of position even if you know the
output is not validated.
This is a feature that can very easily be filtered by monitoring Valid "A" flag and invalid "V" flag in the RMC
message.
Here is an example of a NOT VALID output fix:
$GPRMC,000040.026,V,6016.3376,N,02458.3604,E,0.00,0.00,060180,,,N*73
$GPVTG,0.00,T,,M,0.00,N,0.00,K,N*32
$GPGGA,000041.026,6016.3376,N,02458.3604,E,0,0,,130.5,M,19.5,M,,*42
$GPGSA,A,1,,,,,,,,,,,,,,,*1E
$GPGSV,1,1,00*79
And here is an example of a VALID output fix:
$GPRMC,065343.000,A,6016.3204,N,02458.3279,E,0.02,0.00,190309,,,A*69
$GPVTG,0.00,T,,M,0.02,N,0.03,K,A*3C
$GPGGA,065344.000,6016.3206,N,02458.3278,E,1,7,1.06,29.3,M,19.5,M,,*6A
$GPGSA,A,3,03,22,16,21,27,06,08,,,,,,1.33,1.06,0.81*01
$GPGSV,3,1,12,06,66,201,48,03,65,236,48,22,56,163,48,21,30,090,42*7E
$GPGSV,3,2,12,37,21,183,,08,14,331,34,16,13,204,33,27,09,026,33*76
$GPGSV,3,3,12,07,03,296,30,19,,,45,18,,,48,15,,,37*4C
