Engineering Raw data from GPS receiver

[wacki]

Homework Statement

Calculation of my own position from GPS raw data

Relevant Equations

Just raw data required

I have a school project about GPS and would like to get some GPS “raw data” and then determine my position. There are nice and very detailed descriptions in the net how to perform the calculations, but I have a problem to get some real “raw data”. Ideally, I would collect my own “raw data” e.g. read out some data from my iPhone (I haven't found any appropriate app for that).

It might be naïve, but I’m dreaming of some “raw data” in human readable form like a table with an entry for each received satellite signal e.g.

Satellite No, Signal Arrival Time, x , y , z (where x,y,z are the current Cartesian coordinates of the satellite)

I can live with other human readable formats as long as the conventions are clear as well

So far I haven’t even found some “real life” example data (observed from an arbitrary point on earth), but my own “real life raw data” would make the project really more tangible and personal.

All help greatly appreciated!!

 

[Baluncore]

The problem is that you need correlators and multiple channel receivers to get the raw data. That is built into the GPS receiver module.
The GPS receivers produce a string of serial data every one second.
There are many different strings you can use to communicate with the GPS receiver, to obtain additional data, or to change the mode of operation.
That contains all the processed data you need in human-readable form.
The formatting of the data follows a NEMA standard.
https://www.gpsworld.com/what-exactly-is-gps-nmea-data/
https://www.academia.edu/37808562/GPS_Data_formats_An_Introduction_NMEA_format

 

[pbuk]

Ideally, I would collect my own “raw data” e.g. read out some data from my iPhone (I haven't found any appropriate app for that).

I am pretty sure iOS does not make raw GPS data available to applications so that is not possible.

In theory this is possible in Android but I am not aware of any application that is available.

There are GPS modules available for Arduino/Raspberry Pi etc. and this is the only practical way to access the data you are looking for. Note that raw signal data is not part of the NMEA standard and not all modules support it: those that do use vendor-specific protocols such as ublox's UBX.

I have a school project

When you say "school", what level is this (I notice you were asking questions about QM and GR 10 years ago)?

 

[wacki]

The problem is that you need correlators and multiple channel receivers to get the raw data. That is built into the GPS receiver module.
The GPS receivers produce a string of serial data every one second.
There are many different strings you can use to communicate with the GPS receiver, to obtain additional data, or to change the mode of operation.
That contains all the processed data you need in human-readable form.
The formatting of the data follows a NEMA standard.
https://www.gpsworld.com/what-exactly-is-gps-nmea-data/
https://www.academia.edu/37808562/GPS_Data_formats_An_Introduction_NMEA_format

Thanks a lot for your comment and the 2 links for the NEMA standard!
When I said "raw data" of course I was thinking of pre processed data. Something like the the communication string (in NEMA standard) you mention.
If the The GPS receivers would produce such a string that would be wonderful, but my iPhone doesn't seem to expose this data.

 

[Baluncore]

GPS modules are low cost, less than $10, and can be connected through a microcontroller, that can be programmed to read (and write) the NEMA strings, to display, or to send that data to a personal computer.

Search 'Raspberry Pi GPS' or 'Arduino GPS' to see ways of reading the NEMA strings or making your own navigation system.

https://discussions.apple.com/thread/252823306?sortBy=rank

 

[wacki]

I am pretty sure iOS does not make raw GPS data available to applications so that is not possible.

In theory this is possible in Android but I am not aware of any application that is available.

There are GPS modules available for Arduino/Raspberry Pi etc. and this is the only practical way to access the data you are looking for. Note that raw signal data is not part of the NMEA standard and not all modules support it: those that do use vendor-specific protocols such as ublox's UBX.


When you say "school", what level is this (I notice you were asking questions about QM and GR 10 years ago)?

Thanks for your hint. I might try it with the Samsung of a friend of mine.

You are very observant, indeed my school days are over . I'm supposed to supervise a GPS project at my daughter's school. But I wanted to make it fun (real life data not data from years ago, data of our own position not a random place on earth, using "kind of raw data" but without boring data pre processing). With GPS there is a lot to learn about geometry and iterative solutions of simultaneous equations.
I'm totally baffled by the fact that there are so many useless apps on the iPhone but none that let's you explore the GPS data in a sensible way.

 

[wacki]

GPS modules are low cost, less than $10, and can be connected through a microcontroller, that can be programmed to read (and write) the NEMA strings, to display, or to send that data to a personal computer.

Search 'Raspberry Pi GPS' or 'Arduino GPS' to see ways of reading the NEMA strings or making your own navigation system.

https://discussions.apple.com/thread/252823306?sortBy=rank

Wow, just 10 bugs sounds affordable. Thanks a lot for this hint!!
I'm now convinced that I'll never get the data I want from the iPhone (with so many useless apps from the app store)

 

[CrysPhys]

I'm totally baffled by the fact that there are so many useless apps on the iPhone but none that let's you explore the GPS data in a sensible way.

I'm now convinced that I'll never get the data I want from the iPhone (with so many useless apps from the app store)

Why are you so surprised? Most end-users are only interested in the location coordinates processed from the GPS data. Just as most end-users are only interested in the texts, voice transmissions, and webpages processed by the phone, not the raw digital streams. You're expecting way too much from a consumer end-user device.

 

[pbuk]

GPS modules are low cost, less than $10, and can be connected through a microcontroller, that can be programmed to read (and write) the NEMA strings, to display, or to send that data to a personal computer.

Search 'Raspberry Pi GPS' or 'Arduino GPS' to see ways of reading the NEMA strings or making your own navigation system.

https://discussions.apple.com/thread/252823306?sortBy=rank

For clarification, the $10 GPS modules only produce NMEA sentences, not the raw GPS data (unless anyone knows different - there may be stuff available direct from Chinese markets that does more).

These cheap GPS units are fantastic, I use them instead of real time clocks as they are cheaper and more accurate and can particularly recommend those based on the Grove Air530 module (although the documentation is in Chinese it can easily be translated via an online translation service, or pre-translated versions are available on the interweb). But for a school project this wouldn't be very useful as all you can do is echo the position data NMEA sentences.

If you want raw GPS data (and this would make an excellent high school project) then you need to spend a little more: e.g. about USD 50 for something based on the ublox chip I mentioned earlier.

I'm totally baffled by the fact that there are so many useless apps on the iPhone but none that let's you explore the GPS data in a sensible way.

This is Apple's choice - the data is simply not exposed to applications.