Posted by: Ger Rietman | June 8, 2008

Not so raw NMEA data

Not so raw!

In many articles and other publications NMEA sentences are referred to as ‘raw NMEA data’.

I think this is rather confusing and maybe even misleading since NMEA sentences are very well formatted as normal, readable text. Everybody who has learned to read, can read and interpret a NMEA sentence.

In my opinion NMEA sentences are fairly ‘well done’, instead of ‘raw’. They can be read and edited with a normal text reader like Notepad. They can be easily parsed by application programs aimed at e.g. displaying position information from a GPS, or depth from a depth sensor.

I can imagine that some people are hesitating to implement a simple NMEA parser just by the fact that ‘it is RAW DATA so it must be difficult’. No, it is not. You do not need to be an expert to import a bunch of NMEA sentences and format them for example into nice columns into an Excel data sheet. Well, supposing you know how to use Excel  of course.

Let’s take the following GPS positional NMEA sentence and dissect it:

 $GPGLL,5300.97914,N,00259.98174,E,125926,A*28

Quite readable, is it not? Raw? Come on…

The comma separates each parameter in the sentence, so lets take them one by one.

  • $GPGLL is the identifier ($GP means that the data is coming from a GPS, GLL is the type of sentence)
  • 5300.97914 is the latitude (53 degrees, 00.97914 minutes) 
  • N is ‘North’ (can be N (north) or (S) south)
  • 00259.98174 is the longitude (002 degrees, 59,98174 minutes)
  • E is ‘East’ (can be E (east) or (W) west)
  • 125926 is the time the GPS position fix is taken (12:59:26 UTC)
  • A means ‘data active’ (if ‘V‘ then data void)
  • *28 is the checksum (forget for now)

  
So that is fairly ‘well done’, is it not?

For more information on the NMEA protocol standard see the NMEA page on the Sailsoft website.

 

 

 

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Responses

  1. Hye, just wanna ask, what if the raw nmea data is combined with other data such position or heading and they are all mixed in excel (it’s a sonar data). How can I arrange it if it’s like that ? I can send you the data if you want. Thanks in advance.

  2. I have emailed you a personal message.


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