NMEA feeds

[+Airmapper]

I've been tinkering with this program HERE and a few others.

 

I hooked up my Garmin 72 to the Laptop, and using a feature of the above program can actually see the NMEA feed. Using another program (GPS Trackmaker) I can see there are different types of feed, as in the info carried and it's use.

 

In the visual GPS program, the satellite status and signal strength windows don't show data, so can I assume the Garmin 72 is not sending this data? I can get a survey window, and the program "sees" my GPS.

 

I don't really have a specific question, I just want to know more about NMEA feeds and what I may be able to do with it. So far some of this NMEA reading software looks cool for trying to survey, and get live on screen satellite tracking.

[+Alan2]

NMEA is the communication's protocol that's a standard in the industry. It allows manufacturers when they make products to include the standard NMEA "translation" protocol so that other products can transmit and receive between the units. For example, when I connect my Vista to my Pocker PC, I switch the GPS to NMEA comm mode so the PPC mapping program can read the GPS data stream which tells it where the GPS coordinates. Without the NMEA standard, it would be like two people trying to communicate with each other while each speaks a different language.

 

Google NMEA to get more info.

[+PDOP's]

In the visual GPS program, the satellite status and signal strength windows don't show data, so can I assume the Garmin 72 is not sending this data? I can get a survey window, and the program "sees" my GPS.

My Garmin76 is the same way but my Map76C does show satellite status and signal strength. It's curious that Garmin hasn't standardized the output between all of their units.

[+Airmapper]

I managed to hook up the AirMap, and it seems to have all the feed types. This is pretty cool, I could track and record the satellite tracks in real time.

[robertlipe]

NMEA is a large (and expensive) spec of its own. It does about a bazillion things, but most are centered around a device spitting up periodic position reports to zero or more listeners. There is a lot of information in those reports, but much of it is useless to a Streets & Trips-like substance that just wants to plonk your position on a map. To programs that want to graph the satellite constellation used to derive DOP and such, it's more interesting. In NMEA, almost every sentence is optional so you can have NMEA devices that all conform to the spec but send wildly different types of information.

 

The other competing protocol in the product space that's most interesting to this crowd is Garmin's PVT.

 

http://www.gpsinformation.org/dale/nmea.htm

http://www.werple.net.au/~gnb/gps/nmea.html

 

are sources of information on the NMEA sentences (not so much the electrical specs as I just plain don't care about those) that I refer to when I have to split hairs about such thigns.

[ossumguywill]

I believe that you can view your position on a laptop. Can anyone give an explanation on how to do this with magellan explorist and garmin units? I do not know myself.

[+Alan2]

Any Garmin, Magellan or other topographic or street type mapping program on your laptop that accepts the NMEA protocol should show your location when you connect your GPS to the laptop. The program description will say something like "connect you GPS, etc."

 

Check the programs' specs.

Edited October 21, 2006 by Alan2

[+park2]

You can usually look at the full, native, unmodified string by running HyperTerm or similar serial communications program. Every second or 2, a new set of NMEA strings will scroll up the screen. NMEA is always ASCII text, so you'll be able to read and understand them easily.

 

After a few sets go by, turn off or unplug the GPS and you'll be able to study the strings (or capture a few to a text file). Some will show time & date, others position, others movement, other routing, others give information as to your destination, etc..

 

You just have to make sure your GPS is in NMEA mode and your terminal program is set to the same baud rate & serial format (4800-N-8-1 usually) as your GPS. Your owners manual should show the serial spec in the back somewhere.

[+Airmapper]

Thanks for the added info everyone.

 

I have been using it some more, and I've noticed that I seem to get another digit of accuracy with NMEA, or it could be the software, I'm not positive. Instead of the standard DD* mm.mmm I get DD* mm.mmmm.

 

I find all this interesting. I have a text file of recorded NMEA for about 2 hours today, so I can look at that some.

 

I do plan to use the GPS to run my mapping software, I have MS MapPoint, (similar to S&T) all I need is a cable for one of my GPS units. (What I'm using now is 3 wires, wrapped around the serial pins, and to the units data port.)

[+Alan2]

I have been using it some more, and I've noticed that I seem to get another digit of accuracy with NMEA, or it could be the software, I'm not positive. Instead of the standard DD* mm.mmm I get DD* mm.mmmm.

 

That's another digit of resolution, not accuracy, something most people get confused with. Instead of thousanths of minutes or about 6 feet per digit, the fourth digit gives you about 8 inch resolution (ten thousanth of a minute)

 

Problem is the GPS system overall provides much less than 6 feet accuracy so the greater resolution doesn't mean anything or provide more accurate coordinates.

Edited October 23, 2006 by Alan2

[ossumguywill]

Unless you have a ProMark™ or something with that much accuracy. Actually, with promark, you could have DDD MMM.mmmmm and still have it be accurate....