gps - Calculate vehicle velocity from NMEA sentences -

gps - Calculate vehicle velocity from NMEA sentences -

i wanted position(latitude , longitude) , velocity of vehicle using sim908 gps/gprs module. module kept in vehicle.

i'm able position(latitude , longitude) of vehicle nmea sentences, velocity, i'm not sure it.

i found in nmea sentence, there $gpvtg contains "speed on ground in km/h".

my question is, "speed on ground in km/h" means vehicle velocity on road? or need calculations actual velocity of vehicle?

if "speed on ground in km/h" doesn't mean vehicle velocity on road, can vehicle's velocity?

what kind of vehicle have? in car, speed ofer ground speed on road. in ship, speed on ground can differ speed through water (as water can have currents). same in air.

the gps can know speed on ground, is real physical motion satellite receiver measures. not currents.

typically value need. water/air speed need special measuring device log.

gps nmea