Computers & Mobile Technology
MAKE Forums – Garmin GPS -> PC?

Img413 71
Super_J_dynamite writes “I have a Garmin eTrex Legend. It has a PC Cable which looks to be nothing more than a DB9 serial cable. I believe the intended purpose of the cable is to upload the ~$99 Garmin proprietary map packs into the GPS. Is it possible to go the other way — to get my coordinates from the GPS into my PC? Has anybody done this? Is there a published protcol or, better yet, a library for talking to the GPS? The idea here is that if I can get my coordinates, I can use 3rd party maps on the PC.” See all the suggestions and applications in the MAKE forums (be sure to join and post too!) Link.

20 thoughts on “MAKE Forums – Garmin GPS -> PC?

  1. There are lots of tools to work with the data coming out of your Garmin. As other comments have stated, the data is “NMEA” protocol, which is plain text. Its a set of feilds (comma delimited), and terminated with a CR. Each record type gives different status on various positional datum (number of satelites in view, current time/date, current lat/lon, etc). There are various websites showing you how to wire up your own serial cable for the unit, but, I bought mine off ebay for $15. [You will need to set the garmin unit to xmit NMEA under the System Settings menu]

    With the cable, you can open up any serial-communications app and see the data streaming out of the unit (i used the nasty old HyperTerminal) – 4800,N,8,1.

    Many apps will accept this data stream and display a moving map (I happen to really like MS’s ‘MapPoint’). The OEM one that comes with the unit sucks.

    To get the “waypoints” in/out of the unit, you can use the OEM product (the sucky one mentioned above), or use one of many shareware apps. I really recommend “GPX Exchange” for this. It connects to the device, pulls all the points out, allows you to upload points, and will even give you a satelite view of your waypoints (via web connection).

    Pretty soon you will get tired of watching NMEA data, and would rather create maps. This is serious fun. A group of dedicated ‘hackers’ figured out how to generate their own Garmin compatible maps and figured out how to upload them into the Garmin. [Good starting point:, or Conceptually, you take a road-map, scan it in via regular scanner. Then set some calibration points to give a starting latitude/longitude. Then you simply “trace” over the jpeg using symbols like “roads”, “rivers”,”cities”.

    I’ve been able to make my own Garmin GPS maps, zap them into the Garmin and use them. I recently went to Thailand and there were no available GPS maps – so I made my own. Great fun.


    USA Photomaps is INCREDIBLE. I searched until my face turned blue for decent software that was free and had an actual use to them. One of the best things about this program is that you can download high res sat data from the net of the area you will be going, then when on the road, it draws from the cache, so you don’t need a connection on the road.

    Geocaching is one of my favorite past times, and USA Photomaps is SO useful when trying to locate a cache. You can also download tracks you have saved in your unit, and it allows you to click on your tracks and see altitude, speed and coords (if your unit has an altimeter).

  3. I got mine with the serial cable and have used it with NetStumbler for mapping WiFi access points and along with Microsoft MapPoint for showing my location in real-time. Pretty much plug and play.

  4. Garmin supports two formats. There’s the NMEA format – which is standard – and then there’s a garmin-specific protocol that lets you do more.

    Google for

    garmin gps interface specification

    and it’s the first hit.

  5. Microsoft Streets & Trips works with your GPS (I have the same one). You can use it while driving and it will update your car position overlaid on the street maps of the US. Worked pretty well back when I had a PC.

  6. I use a mapping program called TOPO! It can read waypoints and routes from my eTrex Legend and many other GPS units. I am sure that many other programs in addition to the ones mentioned above can do the same thing.

Comments are closed.


current: @adafruit - previous: MAKE, popular science, hackaday, engadget, fallon, braincraft ... howtoons, 2600...

View more articles by Phillip Torrone