Understanding Position Fix in PMTK314 Command for GNSS

IoT Modules GNSS Module
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Hello Quectel Community,

I am working on a project that involves GNSS for time synchronization, and I am using the PMTK314 command to configure the NMEA sentence output frequencies. I have a specific configuration where I only enable the GPRMC sentence. Here are two variations of my configuration:

Configuration 1:

#define ONLY_GNRMC "$PMTK314,0,1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0*29\r\n"

Configuration 2:

#define ONLY_GNRMC "$PMTK314,0,4,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0*2C\r\n"

In Configuration 1, the GPRMC sentence is set to output once every one position fix. In Configuration 2, the GPRMC sentence is set to output once every four position fixes.

Could someone explain the concept of a “position fix” in this context? Specifically:

  1. What does it mean to have a sentence output “once every one position fix” versus “once every four position fixes”?
  2. How does this setting affect the data output frequency and potentially the performance or power consumption of the GNSS module?

Any detailed explanations or references to relevant resources would be greatly appreciated. Thank you!

Best regards,
M

2

Hi MArtin2020
The “$PMTK314” command sets the output interval of the positioning statement. “Once every one position fix” outputs positioning data every second.
“Output once every two position fixes” outputs positioning data every two seconds.
It can be understood as “Output once every N position fixes”, outputting a piece of positioning data every N seconds. “N” ranges from 1 to 5.

Changing the output frequency will not affect the performance of the GNSS module. Whether it affects the power consumption has not been tested internally, but even if it does, it will not affect the power consumption too much.