GPS accuracy - new insight

[HarmsWay]

My GPS accuracy was spot on until this past weekend. I was returning from a friends house a week ago and the route was along the side of a mountain and it was raining heavily. The D3 GPS clearly didn't know where I was and was relying totally on the 3D hybrid sensors and VSS which were quite confused. However, once I was clear of the mountain, I got the accuracy back and didn't really think much more about it. My GPS antennae is installed in the dash which obviously is not ideal. Anyway, I didn't use the mapping functions of the D3 for about 5 days but was still driving. Then I switched on the map and it was way off again. The satellite signal was pretty much zero so I decided the antennae had slipped off it's perch inside the dash and fell into the mess of wiring. I popped the D3 out and sure enough there it was. I put the antennae back in place and the GPS signal went back to full strength.

 

This is where I learned something new. I had assumed that the D3 used the GPS first to determine position then supplemented with the 3D sensors, VSS and map matching. That doesn't appear to be the case though. With full GPS signal, I would have expected my location to immediately become accurate, but nope. It started off at the correct location but as I drove to work it got further and further off. So I stopped and cleared the sensor learning status and voila! it pops me back to where I should be on the map and has worked since.

 

My theory is that if you have crappy GPS signal, your learning system is using bad data which will screw up your system once the signal returns.

[John@20Squared]

Interesting...

I've had similar problems with the accuracy of my GPS starting out to be SPOT ON and gradually getting worse and further off. But my antenna hasn't moved at all. It has been mounted in the same position on top of the dash (under the windshield since the install). I guess I'll try and reset the learning status and see what happens. Thanks for the info.

[thelaudogg]

I think you may be onto something here. My unit performs great immediately after I reset the learning status. Over the next couple of days it gets worse and worse.

 

Im getting to where now I reset it practically 3 times a week. Its quite annoying but Im not sure what else to do.

[kruff10]

i`v had my d 3 sense sep 07 and have not hade any gps problem and have never reset the learning status.

[HarmsWay]

Which is the way it would work if you always had a good GPS signal. Mine has been solid as well since the antenna has stayed in the correct place.

 

i`v had my d 3 sense sep 07 and have not hade any gps problem and have never reset the learning status.

[kruff10]

i intalled my att. under the dash, i put some puddy like stuff under it to hold it in place.

[JimD]

This thread looks a lot like the problem I am having with my D3. I installed it about 6 weeks ago. I have the VSS connected and my GPS antenna under my dash. For about the first three weeks the navigation accuracy was just about perfect. I didn't use it for about a week and when I used navigation again, it was no longer doing direction of travel up, but north up and I could not get it to change back. Now it consistently puts me at least near to where I am, but not right on the correct location like it did at first. Is this just the downside of it being almost done with learning? Even worse, it has the direction of travel arrow pointing 180 degrees from my actual direction and frequently gives me warnings to do a U-turn as soon as possible, even though the arrow is progressing toward my destination. It also sometimes fails to notify me that I have reached my destination and it no longer gives me turn by turn voice prompts. I loved this thing at first, but now I am wondering if I made a mistake in getting it. I have not yet tried resetting the learning function or resetting the whole unit, but this seems like really poor performance for what I had hoped would be a nice inexpensive navigation unit.

[jwq]

This thread looks a lot like the problem I am having with my D3. I installed it about 6 weeks ago. I have the VSS connected and my GPS antenna under my dash. For about the first three weeks the navigation accuracy was just about perfect. I didn't use it for about a week and when I used navigation again, it was no longer doing direction of travel up, but north up and I could not get it to change back. Now it consistently puts me at least near to where I am, but not right on the correct location like it did at first. Is this just the downside of it being almost done with learning? Even worse, it has the direction of travel arrow pointing 180 degrees from my actual direction and frequently gives me warnings to do a U-turn as soon as possible, even though the arrow is progressing toward my destination. It also sometimes fails to notify me that I have reached my destination and it no longer gives me turn by turn prompts voice. I loved this thing at first, but now I am wondering if I made a mistake in getting it. I have not yet tried resetting the learning function or resetting the whole unit, but this seems like really poor performance for what I had hoped would be a nice inexpensive navigation unit.

 

Is the input signal for reverse correctly hooked up ??

[JimD]

Good question. It was initially, since it showed the image from my Boyo camera when I shifted into reverse. I had a problem with a connector in the wiring from the camera and I haven't fixed it yet. So I turned that feature off so I wouldn't keep seeing the "no signal" display when I shifted into reverse. I guess I can turn the camera back on and see if it still tries to show an image when I'm in reverse, which would tell me that the reverse sensor wire is still connected correctly. Thanks for the idea.

[HarmsWay]

Everything you need to assess your current conditions is on the "Connection Status" screen. It shows the VSS pulses, the GPS antenna signal strength and the back signal (reverse gear or not).

[JimD]

Good point - all the signals check out OK - so that isn't the problem. I guess I will try resetting the hybrid sensor learning process and/or the whole unit and see if that fixes it. Since so many other people have had similar problems it seems unlikely that it is a defect in this particular unit. I guess I can try to get it replaced as a last resort if resetting it doesn’t help. What is really irritating is that it worked great when it was first installed.

 

This afternoon I am meeting my wife somewhere and I printed out a paper copy of a Google map – it is pretty bad when you do that and you are driving a truck with a navigation system in the dash!

[JimD]

Since all my input signals are correct, I tried resetting the hybrid sensor - and just like that I am right on the actual location on the map and heading the correct direction. Now if I could just figure out why it stopped doing direction of travel up instead of North up I would be back to where it was when I installed it.

[HarmsWay]

Now if I could just figure out why it stopped doing direction of travel up instead of North up I would be back to where it was when I installed it.

Poke the little red/white compass arrow in the lower right hand corner to switch between "Heading Up" and "North Up".

[JimD]

Thanks for the info. I tried that when it was otherwise messed up and it didn't work, but now that it is working correctly I will try that again. I think if it starts doing the same wacky stuff when it finishes the learning process next time, I might unhook the vehicle speed sensor. A friend at work never hooked his up and his D3 is working just fine without it.

[JimD]

HarmsWay - you are correct - now that my D3 is working otherwise correctly I can change back to direction of travel up with no problem. I'm just hoping it keeps on working as well as it is right now - no problems with the cursor pointing the wrong direction or missing turn prompts or anything since I reset the hybrid sensor learning sequence.