GPS Help - Incorrect Lat/Long

GPS/GNSS Development Boards
1

Hello everybody,

I recently created my own GPS board for the Lassen IQ Gps module. After getting it rigged up and connected to my computer I got me some data! I was so amazed. No magic smoke was lost and all the components(-1 blue LED) worked! Within a few minutes of sitting outside under a night sky I even got some actual GPS data! NMEA strings, I was so happy… That is until I put them into google maps… My Lat/Long seem to be off… Not very far off mind you, but off. I appear to be several(~30 miles) SW of my actual position. I don’t really feel comfortable giving out my GPS location so suffice it to say: I’m getting data. I’m tracking 4,er 5, satelites and my GPS fix is “1”(See full NMEA string below). Anybody have an suggestions?

NMEA STRING(Minus GPS Lat/Long ofcourse) reported by GPS

$GPGGA,020637.00,XX194774,N,0YY35.2122,W,1,05,1.86,00055,M,-031,M,*5C

Derived position:

XX.194774N

YY.352122W

Actual Position

XX.324286

YY.5868543

(Note, XX is the same, YY is the same so the GPS Data is in the Ballpark)

(Note 2, I just tried reseting the module, I removed both main power and battery power and I got the exact same results)

2

Congratulations on getting it working. I think it’s actually giving you the right data. When the GPS says 0YY35.2122,W it means YY degrees 35.2122 minutes west, not YY.352122 degrees west. The numbers look pretty close when you convert them.

3

It is giving you the correct information, as the other respondent noted.

Derived position: Actual Position

XX.194774N XX.324286

YY.352122W YY.5868543

Your “actual positions” are in degrees and decimal parts. The “derived positions” are in degrees, minutes, and seconds (that is, 60ths, and 60ths of 60ths). You can think of it as like hours, minutes, and seconds:

1.3242 o’clock is

1 o’clock + .3242 of 60 minutes = 1 o’clock + 19.452 minutes

(pretty close to what you have - I assume there’s some measurement error there, either in the GPS or in how you measured it, or both)

1.5868 o’clock is

1 o’clock + .5868 of 60 minutes = 1 o’clock + 35.208 minutes

(that one is even a little closer to what you have)

Here is some information on the NMEA sentences you’re looking at:

http://home.mira.net/~gnb/gps/nmea.html#gpgga

In short, your device is working fine (congratulations!). You just need to add another step to interpret the output.