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Garmin 128 GPS question

Old 12-25-2002, 09:36 AM
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Default Garmin 128 GPS question

Have had this unit for years with 0 problems and I love it(especially for the price). While sitting at the dock, if I turn the GPS on and "GO TO" a waypoint, it always shows the opposite direction. If the proper direction is East, it will show WEST. The distance is correct for the direction is not. If I then get underway, the direction is corrected. What causes this? It has always done this. Not a problem that I am overly concerned about just curious what the cause is.

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Old 12-25-2002, 02:03 PM
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Default Garmin 128 GPS question

I HAVE A 230 WHICH DOES THE SAME THING. THE BOAT MUST BE MOVING TO GET ON COURSE, WHEN YOU USE WAYPOINTS. THE CHART HOWEVER WILL TELL YOU WHERE YOUR BOAT IS IN RELATION TO YOUR COORDINATES.


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Old 12-26-2002, 11:03 AM
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Default Garmin 128 GPS question

I too have a 128 that does the same thing.
Somebody call GARMIN customer support to answer the question.

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Old 12-26-2002, 01:14 PM
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Default Garmin 128 GPS question

Folks, don't be running off to Garmin's customer support on this one. Maybe I can help you out just a bit.

A GPS has no idea which way it is pointing, and it really wouldn't matter anyway. What if you took the one in your hand while you were standing still, and turned it around. The arrow would then be pointing the right way. If you turned it 90 degrees it would be pointing all wrong. But none of it matters. That's because a GPS is not a compass.

The only way a GPS ever knows which way is which is if it is moving, and even then it makes an assumption. The GPs assumes (via it programming) that it is in front of you, with the screen facing you, and its front facing in the direction you intend to move. The GPS, as I said, does not have any idea which way it is pointing but it can tell which way it is moving.

A GPS only 'knows' one thing. It knows its current location. The GPS also has a bit of memory and it uses it for several purposes, one of which is to remember where it was just a moment ago (usually one second in time ago). The GPS also has a very good internal calculator that is used to do all sorts of nice things that we now take for granted.

So, you're GPS is sitting there with no idea which way it is pointing and you tell it to give you the direction to some place you have stored in memory. It has no idea which way to point the arrow because it has no idea which way it is pointing. But remember that memory it has? Well, it finds its current location, and puts that into the memory. Then you get to moving in some direction. A second later it determines its location again, and this time it will compare its current location to the one it has in memory. Now it can, via that great built-in calculator, determine a couple of things, it can calculate how far away its current location is from the one it saved a second ago and it can calculate in which direction it must have moved to get from where it was to where it is. That is how it determines direction, only by comparing a previous location to a current one. And if you stop moving it will hold your last direction until you move again. Its really that simple. Now, if for some reason you feel you really need to know direction when you haven't moved a bit you could buy yourself a machine like the Garmin GPSMap-76S. It has a built in compass that will give accurate direction when you are not moving. That will cost you though and it would be much more practical to just buy a small hand compass if you really need to know.

Thom

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Old 12-27-2002, 07:11 PM
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Default Garmin 128 GPS question

I have the Garmin 126, same as the 128 but with an internal antenna. You are right about the compass when you "GoTo" a waypoint. What's nice is having the bearing shown and your track. The GPS takes a second or two to catch up once you are moving. I use the real compass for the first few seconds to get me going straight and then look at the GPS.
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