GPS is inaccurate.. Any help??

bobbykokinos · 01-29-2007, 01:09 AM

I'm running a BU-353 into iGuidance and RoadRunner.. I've noticed iGuidance is constantly around 400ft off.. When it says I still have 400ft until a turn, I'm already there.. I've tried to get everything setup right (right com ports, right baud rate, etc..)..

Any help or suggestions??

Edit: If this helps at all, once I come to a stop, after several seconds it'll get CLOSE to the right position.. Also, when I'm not moving, my speed and position tend to "float" around a bit.

wi77iam · 01-30-2007, 07:05 AM

Give us some more info and maybe we can make suggestions. Where is your antenna mounted? How many satellites are you tracking? How fast are you going? Is this gps WAAS capable and do you have it enabled? What mobo/cpu are you running? Normally, a gps position lags you're true position due to inaccuracy in the signal and time delay in the position processing and the speed of you car. GPS is only accurate to about 3 meters but may be 10 meters depending on number of satellites. The software updates at a one second rate, so when travelling at 60 mph, you can go 88 feet between updates. So with a poor signal, you could be up to 120 ft off with a perfectly good gps. 400 ft off seems to be excessive though.

faichiu · 01-30-2007, 09:25 AM

Sounds like you didn't get enough satellites signal.

bobbykokinos · 01-30-2007, 03:24 PM

Quote: Originally Posted by wi77iam

Give us some more info and maybe we can make suggestions. Where is your antenna mounted? How many satellites are you tracking? How fast are you going? Is this gps WAAS capable and do you have it enabled? What mobo/cpu are you running? Normally, a gps position lags you're true position due to inaccuracy in the signal and time delay in the position processing and the speed of you car. GPS is only accurate to about 3 meters but may be 10 meters depending on number of satellites. The software updates at a one second rate, so when travelling at 60 mph, you can go 88 feet between updates. So with a poor signal, you could be up to 120 ft off with a perfectly good gps. 400 ft off seems to be excessive though.

Antenna is mounted on the very front of the dashboard butted up to the window.. Last time I checked, it was tracking 9 satellites. The BU-353 is WAAS enabled and I believe its set to be on from the factory. To be honest, I don't know how to turn it on if its off.. I'm I'm running a Jetway J7F2WE with a Via C7 processor (1.5ghz)..

Hope that helps..

wi77iam · 01-30-2007, 06:34 PM

Quote: Originally Posted by bobbykokinos

Antenna is mounted on the very front of the dashboard butted up to the window.. Last time I checked, it was tracking 9 satellites. The BU-353 is WAAS enabled and I believe its set to be on from the factory. To be honest, I don't know how to turn it on if its off.. I'm I'm running a Jetway J7F2WE with a Via C7 processor (1.5ghz)..

Hope that helps..

It sounds like everything is set up and working correctly. I normally have 9 to 11 sats tracking, but I'm using a SiRF III gps. In any case, it doesn't seem like it should be 400 ft off. Is that consistent, ie all the time 400 ft off? Maybe mount the antenna on the roof if possible to see if that makes a difference - you want as clear a view of the sky as possible.

bobbykokinos · 01-30-2007, 10:02 PM

Quote: Originally Posted by wi77iam

It sounds like everything is set up and working correctly. I normally have 9 to 11 sats tracking, but I'm using a SiRF III gps. In any case, it doesn't seem like it should be 400 ft off. Is that consistent, ie all the time 400 ft off? Maybe mount the antenna on the roof if possible to see if that makes a difference - you want as clear a view of the sky as possible.

Well, it seems as if its more accurate now at about 100ft.. Is this about right or should it be more accurate??

Also, I talked to the manufacturer and they said it should be WAAS enabled from the factory. Well, they gave me the codes to figure out if it actually the WAAS is enabled but, from what I can tell, its not.. Is there any software out there I should look at to enable it?

wi77iam · 01-31-2007, 03:20 PM

I know that Street Atlas has a check box to turn WAAS on and off. I don't know about other software, but I'm assuming that they will use WAAS capability if it is available and the satellite is in view.

Oh, and 100 ft seems about right for accuracy under normal driving conditions.

sebberry · 01-31-2007, 10:55 PM

GPS should be accurate to about 30 feet...

wi77iam · 02-01-2007, 12:44 PM

Quote: Originally Posted by sebberry

GPS should be accurate to about 30 feet...

. . . . 30 feet for a stationary object. Factor in the one second latency of most mapping software and, for a car moving at 60 mph, the accuracy (ie, how far off your displayed position is from your actual position) is about 100 feet.

DK888 · 02-01-2007, 07:30 PM

Try this.... Put a piece of metal under the GPS, allowing the GPS's magnet to stick to it. I had the same problem and I NEVER had a problem after this.