GPS Ingest v1.0

Paul_H · 2007-05-23 22:54

Hello All,

It's been a while since I contributed and I've finally gotten my GPS Ingest routines together for your use, comments and review. These routines read and parse GPS NMEA strings to variable locations on the fly. Special thanks for Phil Pilgrim and MK Borri for their inspiration and code snips. So far I have copied the routines out for four common NMEA strings.

  $GPRMC  Recommended minimum data                ie: $GPRMC,081836,A,3751.65,S,14507.36,E,000.0,360.0,130998,011.3,E*62
  $GPGLL  Geographic Position, Latitude/Longitude ie: $GPGLL,4916.45,N,12311.12,W,225444*7B
  $GPGGA  GPS Fix Data                            ie: $GPGGA,170834,4124.8963,N,08151.6838,W,1,05,1.5,280.2,M,-34.0,M,,,*75
  $PGRMZ  GARMIN Barometric Pressure Altitude     ie: $PGRMZ,707,f,3*1B

The START routine calls a demo which looks for the three $GPxxx strings, parses and displays what ever is available. I've been using the free GPSSimulator program at http://www.sailsoft.nl/ for development.

I want you feedback and comments as this is a work in progress.

Roadmap:
1. Instruct the serial i/o to Not wait for each string so it won't get stuck if a string doesn't arrive.
2. Figure out how to use variables directly (rather than use @ with everything!)
3. Determine if I really need explicit variable size definition.

When this is a little cleaner, I'll post to the object exchange
Thanks for you comments!
Paul

Questions/Comments/Suggestions?
1. Do you think it is better for each PUB procedure to return all the variable when called ie GPRMC, or to assign them to preexisting global variables as I do now?

.

Paul_H · 2007-05-23 23:00

Also, feel free to play with the code and use where you'd like. This code is bulky because it assigned everything in the NMEA string. One of my goals is to make a general purpose GPS object, so you may want to pare it down to just the values you need.

Paul

Larry · 2007-05-23 23:26

Nice job.

Is the GPRMB sentence on your list of sentences to add?

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M. K. Borri · 2007-05-24 01:07

awesome!!!!!

If you want a parser for the Garmin simpletext format, feel free to grab it from my sig. Can I mess with your parser a bit and add sentences?

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http://forums.parallax.com/showthread.php?p=650217

meow, i have my own topic now? (sorta)

Paul_H · 2007-05-24 01:53

Thank Matteo,

Please use, change, add or mod the code anyway you want - change is good, and I appreciate your help as I plodded along

I downloaded your project the day you posted it, and it in mind to put the values (like Lat and Lon or Time) into a mathematically usable formats. I had done these 4 sentences to get the conversation started around what is the best general way to acquire and preserve the data.

Larry,

It is pretty easy to add new sentences - I'll put it in the next release. In the meantime, check out the code and see if it presents the data best way for you (or copy a PUB and give it a try)! Phil Pilgrim's parsing code does all the real work. My part is a pretty repetitive process that needs only 3 thing: VAR names assigned in the VAR section, the sentence grabbed in the PUB GPXXX, and a display, but the display is just to show it is working.

Have fun,
Paul

M. K. Borri · 2007-05-24 02:17

There's one major problem with latitude and longitude -- you're generally better off keeping them as integers, because if you use 32-bit floats you'll lose the final digit to imprecision, sometimes (the "sometimes" is the worst part actually, it's not very deterministic).

My next revision will try and get around it, but i'm considering 64 bit math eventually... maybe for the next chip if it has more ram.

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http://forums.parallax.com/showthread.php?p=650217

meow, i have my own topic now? (sorta)