Androiders, I need your data
The attached pfd article explains the meanings of DTM, GGA, and GNS NMEA sentence types.
Have you ever looked at your smartphone??s displayed ground elevation, often referred to as Alt MSL, and wondered if something wasn??t quite correct? Well, trying to get to the bottom of it will take a little effort, but thanks to the growing list of Android apps capable of capturing NMEA sentences, most of the work is in deciphering the terse NMEA messages.
There are 2 primary sentence types to look for, GGA and GNS as they contain the geoidal separation values(1) from which the orthometric (H) values are derived. To discover the correct geoidal separation (N) value for your location, search online for interactive calculation tools(2), and then compare it to the value in the NMEA sentence. The DTM message is also worth looking at as it can play a role in determination of heights(3).
Most apps will give you your ellipsoid height (h), often referred to as Alt, and some apps may only display this value.
There are many Android apps capable of logging NMEA messages. You will need only one for this request: 2 to 3 minutes worth of static data on any station under open view of the sky. If you’re undecided, these 3 apps offer NMEA logging, and much more.
- GPSTest (barbeauDev) – can also log raw obs!
- GnssLogger (Google) – can also log raw obs!
- Ultra GPS Logger (FlashLight)
My Ask of You
Email your results with any screenshots, and please include the name of the manufacturer, make and model of your android device to kellybellis at gwi.net with the subject: NMEA data for you!, and thank you very much for your participation!
(1) Geoid models that are used by chipset manufacturers and OEMs may vary
(2) E.g., xGEOID20 Interactive Computation Page; Computation of GEOID18 Geoid Height; GeoidEval; Geoid Height Calculator (EGM96); any my personal free stand alone fav, VDatum.
(3) Local geodetic datums and datum offsets from the reference datum used by chipset manufacturers and OEMs may vary
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