What is the "NavSpeed" or "Nav Speed" mode?

[Horsa]

Q: What is the NavSpeed or Nav Speed mode?


The NavSpeed or Nav Speed mode is a default firmware option designed for most navigation applications.

As of firmware checklist v101119, it is no longer enabled by default on the latest GlobalTop GPS receivers and modules. It performs only non-linear filtering with a default threshold speed of 1.0 m/s. The value of the threshold speed can be adjusted or disabled completely depending on customer's preferences. GlobalTop has determined though that 1.0 m/s is a good value to work with, because it reduces GPS drift without having any sensible impact on usage.

The basic idea is that the GPS engine will be more likely to ignore (or reject) data if the speed between two data points is lower than the threshold. But not all data are reject because there are some other factors that will effect this decision. So what the user will typically see is a reduction in the GPS drift phenomenon.

Nav Speed Threshold was enabled by default because GlobalTop wanted the customers to test its modules with this feature on. GlobalTop received many requests from customers to reduce the GPS drifting problem, so they chose to have this turned on with no other options.

Now the NavSpeed or Nav Speed mode can be dynamically turned on/off and adjusted by GlobalTop PMTK proprietary commands in a volatile way.

Packet Type:397 PMTK_SET_Nav Speed threshold
Packet Meaning: If the speed is slower than the specified threshold, the output position will stay freezed.
Packet type: command (sent to the receiver)
Data Field: PMTK397,Nav Speed threshold
Nav Speed threshold: 0.0/ 0.2/ 0.4/ 0.6/ 0.8/ 1.0/1.5/2.0 (m/s)
Disable: Nav Speed threshold is set to 0 m/sec

Example:
$PMTK397,0.2*3F<CR><LF>
$PMTK397,2.0*3F<CR><LF>



Packet Type: 447 PMTK_Q_Nav_Threshold
Packet Meaning: Query current Nav Speed threshold setting.
Packet type: command (sent to the receiver)
DataField: NONE
Return: PMTK_DT_Nav_Threshold

Example:
$PMTK447*35<CR><LF>



Packet Type: 527 PMTK_DT_Nav_Threshold
Packet Meaning: Current Nav Speed threshold setting (response packet)
Packet type: response (sent by the receiver)
DataField: PMTK527,Current Nav_Threshold
Current Nav_Threshold: The range is 0/ 0.2/ 0.4/ 0.6/ 0.8/ 1.0/1.5/2.0 (m/s)

Example:
$PMTK527,0.20*02<CR><LF>
$PMTK527,2.00*02<CR><LF>
$PMTK527,0.00*00<CR><LF>

More info here:
  http://docs.trenz-electronic.de/GlobalTop_Technology/firmware/