Decode your T3 NMEA GPS Data

A great feature when using the T3 is the use of a Windows Laptop PC app (in this case, Visual GPS) that can save all the NMEA data sentences to a file throughout the launch until the rocket drops below your line-of-sight data link.

Once these sentences are captured, you can read the sentence data to confirm the altitude being reported from your RRC2 or RRC3.  In addition, one can also calculate the rocket’s velocity at any number of points during the launch, the arc distance from the pad for  apogee and popped the drogue, the descent velocity, and the exact distance from the launch rail to the last recorded coordinate.

For the this exercise you only need to look at the $GPGGA data sentence. That gives you the time (UTC), latitude, longitude and altitude (above sea level).  The first two pages of the this excellent document give you everything you need to know for reading all the GPS sentence data fields. The rest of the document takes a deeper dive into the geographic coordinate system (GCS) trigonometry that would assist someone that wants to learn more about the underlying math it takes to calculate the GPS location (such as university students or anyone else wanting to write their own code for post-flight analytics).

Below we've captured an example of an NMEA Sentence as a brief preview into what you'll see in the data set.