Erratic Directional Needle

[+KBer]

I wonder is there someone can give me a good explanation, on why the directional needle on my GPS unit at times gets to be very erratic. I understand why the unit would be erratic while I am within the error distance of my destination. But sometimes for no reason the arrow points all over the compass, but the distance seems to work fine.

[umc]

What unit do you have?

 

______________________________________________________________________________________

Coming Around, New Owner Of a Garmin GPS V Received on 10-03-02

[+KBer]

I have a Garmin Etrex Vista.

 

But I have heard that other people have the same problem.

[+raouljan]

How close to the co-ords are you, and..

How fast are you moving?

 

>Personally Responsible for the Recovery of .00244% of the Benchmark Database!<--watch this number!

[+KBer]

This can be when I am a mile or so away. Sometimes when I go to a cache everything is fine, then on my why back along the same path I get an erratic needle.

[+raouljan]

Walking? Driving? Changing speeds?

 

>Personally Responsible for the Recovery of .00244% of the Benchmark Database!<--watch this number!

[+KBer]

This is when I am walking. The problem never appears when I am in the car driving. In the car the directional arrow is always solid.

[+apersson850]

Do you have the magnetic compass enabled?

If you haven't changed the default speed for that one, it will kick in below 16 km/h (10 mph), which probably is above your walking speed. The magnetic compass, while being able to tell the direction with the unit at standstill, is sensitive to the angle you hold the unit at. So, if you unit is "listing" to the right, it will give some other direction, compared to when held level or tilted in some other direction.

 

Anders

[+Jamie Z]

I would attribute this to the slow speed at which you are moving. Essentially, when you are walking, you are almost standing still... at least according to the GPS.

 

Think about it. When you walk, you are moving at roughly four feet per second. The GPS takes a reading every second, and its error is somewhere around 20 or 30 feet. It would be very easy for it to think you are actually walking in a different direction or even backwards.

 

The slower you move, the more pronounced this error is, until when you are standing still, the GPS can have no way of knowing which direction it is facing.

 

Jamie

[+Prime Suspect]

Once you start walking above a certain speed, the unit switches from the internal electronic compass (assuming you've turned it on) to infering your orientation from your direction of travel (which assumes you have the unit pointed in the same direction your are moving). It does this by determining your current position, and comparing it to your position a short time ago. When in your car, you've moved far enough between readings that the directional calculation is fairly accurate. When walking, your going slow enough that normal positional errors can influence the calculation.

 

[+KBer]

What is the solution? Turn off the internal compass? Only taking readings standing still?

[+apersson850]

A GPS doesn't use only "where were you before and where are you now" to determine the speed. It also uses the doppler shift on the signals from the satellites.

 

It's necessary to hold the unit level, to be able to use the magnetic compass. Myself, I use both, but I set the threshold for the magnetic compass as low as four (4) km/h. Thus, my ordinary walking speed is enough to keep it off, until I stop completely. While moving, the GPS derived compass is better, since it's independent of how you hold the unit (assuming you hold it in such a way that you can get satellite reception).

 

Anders

[+BruceS]

One other thing to check. Insure you are using bearing pointer instead of course pointer. Course pointer tries to get you on a straight line to destination from where you started and the bearing pointer does it from where you are currently. I had mine set wrong for a couple days on a recent trip had me confused for the whole time.

[+Prime Suspect]

quote:

---

Originally posted by Anders:

While moving, the GPS derived compass is better, since it's independent of how you hold the unit (assuming you hold it in such a way that you can get satellite reception).

---

 

That's debatable. While it's not necessary to hold the unit level, orientation is still important. The GPSr has to assume that you're holding the unit so that it's pointing in your current direction of travel. If you're holding it, say, 10 degrees off, the arrow will be pointing 10 degrees off.

 

[+apersson850]

Well, well, I'll say it's not debatable, but maybe interpretable. I still say that it will point in the correct direction, relative to the unit itself then, regardless of how you hold it, as long as the signals can reach the antenna properly.

 

However, if you are confused enough to hold your unit backwards, it will most certainly point you back to where you came from.

 

Anders

[PonderingPawn]

I dont know if you done this??

 

But my vista did the same thing after putting new Batteries in. and you want to CAL it with no metal present. Then mine worked great.

 

Or do you have a metal watch or something to close to the unit??

 

Ponderingpawn

[+TinSparrow]

I have an eTrex Venture (no compass built in) and this units exhibits the same erratic pointer behavior. It typically happens at walking speeds, and typically when my view of the sky is not "perfectly" clear. Let me stress the "perfectly" clear part, since I also carry a lower priced Magellan 310. I bought the Garmin eTrex as an upgrade, but I find the the Garmin loses signal far more frequently than the Magellan unit does. This is a very annoying problem, and one that will force me to move away from this product line in the future. I like the features, I'm okay with the interface, but the performance is way below what I had hoped for.

[+Searching_ut]

The compass jumps around because the position where the unit thinks it is jumps around. With an etrex, slight differences in the way you're holding the unit will cause it to jump quite a bit in poor reception areas. Learning how to hold and interpret the readings takes time and practice. If you have one of the newer Magellan units such as the sportrak, they average and otherwise process the positional data even while moving, which smooths out the needle somewhat, but can make the positional readings quite a bit more innacurate while on the move.

 

Personally, I prefer the jumping around pointer to the buffered one, but it all boils down to which gives you the info you need in a way that works

 

For what it's worth

 

Jeff

[+SecretSpy]

Calibrate it after battery changes and set the turn off speed to less than 5mph and you're good to go. Like Anders Itrust the Mag when I'm stopped and GPS when I'm moving. I'm in the habit of calibrating mine when I get out of my truck and start walking to the cache.

 

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