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NMEA GPGGA GPVTG (Steered Point) - 15


 Driver for NMEA-0183 $GPGGA and $GPVTG output strings.

Driver to be used to generate output strings containing position and solution results from the Qinsy system.

The NMEA output driver has three different types of output modes:

  1. Skewed Position:  position at update time with update time; age is 0 seconds by definition
  2. Steered Point: position for currently active steered point, determined by the Controller
  3. Sounding Datum: output height above sounding datum instead of WGS84

Driver Information

Driver NMEA GPGGA GPVTG  Interface Type
Driver Class Type
UTC Driver (question) No Input / Output Output  Executable DrvOutNMEA.exe 17 
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Encoding Notes

Qinsy does not encode the geoidal separation and reference station id fields. Latitude and longitude are always given in 4 decimals. The antenna altitude is given with respect to the WGS84 ellipsoid.

The age of the differential data will be the age value of the most recent differential correction observation, since each correction observation can have its own age (especially in case of a Sercel HF link).


Controller Setup

Except when the "Steered Point" option of this driver has been selected, the appropriate output node must be selected before the driver starts cycling. After going online with the Controller for the first time, select an output node in the Computation Setup.

In case of outputting the Steered Node position, the user has to set up also one or more Steered Points.

Steered point output

If the computation fails for the current steered point, its position will be predicted for the number of seconds set in the Filter option in the Controller (default 10 seconds) and then changed automatically to the next steered point. If there is no more steered point left, the last known position will be outputted.

With DGPS, the quality indicator Q will be 2 in case everything is OK. Q stays 2 during prediction. If the prediction is caused by No Diff (Stale Corrections), then the number of satellites in use stays the number of satellite observations. If the prediction is caused by e.g. No SVs, then the number of satellites drops to 0.

If the prediction time exceeds 10 seconds, Q will change to 1. This 10 seconds is hard-coded in the driver.

If the filter prediction time is passed, the Controller will swap to the next steered node. If there is no next steered node defined, output will be the last known position, and Q = 0.

If the steered node position comes from an computation that does not contain differential corrections, e.g. with standalone GPS, Q is always 1, also during prediction, and swaps to 0 when prediction time is over. During prediction, the number of satellites will drop to 0. The age of the differential data will always be 0.