12 satélites es el límite que tiene el protocolo NMEA.
Para ver más información:
- View > Messages View, click con el botón derecho en NMEA y selecciona Disable Child Messages
- Click con el botón derecho en UBX y selecciona Enable Child Messages
Ahora deberías ver bastante más información.
Respecto al tipo de Fix que obtienes, estás usando correcciones NTRIP o correcciones en configuración base-rover?
You can even get FIX with less than 7 satellites. But critical factors affecting RTK accuracy that need to know are :
Environmental factors that impact GPS measurement quality include:
Base station coordinate accuracy.
Incorrect or inaccurate base station coordinates degrade the rover position solution.
Number of visible satellites.
A GNSS position fix is similar to a distance resection. Satellite geometry directly impacts on the quality of the position solution estimated by the receiver. The Global Positioning System is designed so that at least 5 satellites are above the local horizon at all times. For many times throughout the day, as many as 8 or more satellites might be above the horizon. Because the satellites are orbiting, satellite geometry changes during the day, but repeats from day-to-day.
A minimum of 4 satellites are required to estimate user location and time. If more than 4 satellites are tracked, then an over-determined solution is performed and the solution reliability can be measured. The more satellites used, the greater the solution quality and integrity.
The Position Dilution Of Precision (PDOP) provides a measure of the prevailing satellite geometry. Low PDOP values, in the range of 4.0 or less, indicate good satellite geometry, whereas a PDOP greater than 7.0 indicates that satellite geometry is weak.
Even though only 4 satellites are needed to form a three-dimensional position fix, RTK initialization demands that at least 5 common satellites must be tracked at base and rover sites. Furthermore, L1 and L2 carrier phase data must be tracked on the 5 common satellites for successful RTK initialization. Once initialization has been gained, a minimum of 4 continuously tracked satellites must be maintained to produce an RTK solution.
When additional constellations such as GLONASS are tracked, one of the satellites will be used to resolve the timing offsets between that constellation and the GPS constellation. Tracking additional satellites will aid in the RTK solution.