Help choosing GPS for tracking velocity/location

[Joseph Ko]

Hello,

I am looking for a handheld GPS device that will log velocity and location at one second intervals (at least). This is for research purposes and measurements will be taken in a relatively dense urban area. I've looked into the Garmin etrex 20x and saw that it can track information at a log interval of 1 second, but it doesn't seem like velocity would be recorded as part of that tracking information. Any help would be appreciated. Thanks!

Joe

 

[Nuvi-Nebie]

As far as I am aware no GPS unit logs velocity, they only log time, location and altitude, however velocity can be calculated by determining how far the unit has travelled in a certain amount of time, I.e. if the unit logs a location every second and two locations are 25 metres apart, then the unit was travelling at 25 metres per second or 90 kilometres per hour

 

[Joseph Ko]

As far as I am aware no GPS unit logs velocity, they only log time, location and altitude, however velocity can be calculated by determining how far the unit has travelled in a certain amount of time, I.e. if the unit logs a location every second and two locations are 25 metres apart, then the was travelling at 25 metres per second or 90 kilometres per hour

Thanks for the response. I guess what I was wondering was whether some devices would have built-in post processors to calculate/log that "in real-time" since I noticed that the etrex does show "real-time" velocity on the main screen. I understand that the calculations are trivial and can be implemented really easily but I was just wondering if there would be any units that logged it in the first place. Seems like it's not a variable that GPS trackers log.

 

[Nuvi-Nebie]

As you say the calculations are done on the unit so that 'speed' can be displayed, however the only logging I have seen is either NMEA sentences (which don't contain velocity), or tracks in the form of GPX files, these files only contain time, location and altitude and I'm guessing are just converted from the NMEA sentences. So the calulated 'speed' doesn't get logged, if you view a GPX track file in a computer program like Garmin Basecamp, a 'speed' is displayed, but this value is calculated by the Basecamp program frim time / location data

 

[Joseph Ko]

As you say the calculations are done on the unit so that 'speed' can be displayed, however the only logging I have seen is either NMEA sentences (which don't contain velocity), or tracks in the form of GPX files, these files only contain time, location and altitude and I'm guessing are just converted from the NMEA sentences. So the calulated 'speed' doesn't get logged, if you view a GPX track file in a computer program like Garmin Basecamp, a 'speed' is displayed, but this value is calculated by the Basecamp program frim time / location data

Got it. Thanks for the further clarification. This will be my first time trying out this kind of handheld GPS device so it's useful information.

 

[Nuvi-Nebie]

I have had another look into this and although the speed data is not in a GPX 'track' data, it does look like some unit including the Etrex output some 'calulated' NMEA sentences, have a look at the GPRMC sentence, this does contain speed data here :-

http://aprs.gids.nl/nmea/#rmc

 

[Joseph Ko]

I have had another look into this and although the speed data is not in a GPX 'track' data, it does look like some unit including the Etrex output some 'calulated' NMEA sentences, have a look at the GPRMC sentence, this does contain speed data here :-

http://aprs.gids.nl/nmea/#rmc

This is interesting. And hopefully I can extract the NMEA sentences easily in a readable format. Thanks for going above and beyond on this!