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Locomotiveman

Back to GPS Waypoint, How ACCURATE?

16 posts in this topic

Is GPS always 'On the Money' when returning to a waypoint? I earlier thought my Lakemaster chip was off or I needed Lowrance MapFix, but 37C Owners Manual sez, "...first set a Waypoint (a buoy/dock)then motor away and then hit the keys Navigate/Reverse/Enter to return. OK,so far so good; But when returning from South I'm off to the Left and when returning from North I'm off to the Right. QUESTION: Must I first ZOOM/IN maximum at the Waypoint to get it 'On the Money'? Wuzzup? Locomotiveman

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Depends on your error positioning when you set your waypoint. If you set a waypoint and your gps has low satelite at the time, you could be off by 15 to 300ft.

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The same is true when you return. If your GPS accuracy at that time is also off, your margin of error could be significant.

Suppose your GPS accuracy is 15 feet when you record your waypoint. That's a 15 foot radius. This means that the position you recorded could be off by as much as 15 feet in any direction.

Now suppose your GPS accuracy is 15 feet again when you return. Again, where it says you are could be off by as much as 15 feet in any direction.

The actual place you were at when you recorded your waypoint could be anywhere up to 30 feet away.

That's one reason I like my Garmin. I often see GPS accuracy to within 6 or 7 feet. From what I hear, Lowrance products don't seem to boast that kind of accuracy. Maybe they do but if so, nobody's talking about it.

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I'm usually pretty accurate with my lowrance, but at the same time just use it to get back in the general are. Fish won't be in the exact spot anyway. So get to that area and search. If you are within 30 feet you should be able to find them again if they are still there.

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I have returned to an ice fishing spot marked on the gps and actualy drilled right next to (1-2feet) my old holes. I didn't even realize it untill I melted off some of the snow inside the house. This was a full month from the last visit to the spot. W/a Lorance h20 and a lakemaster chip.

I do agree with the above statements and always look at my waypoints as just a suggestion. But if I can fall within 20' or so, that is close enough for me.

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yep, all depends on your position error. I never set a waypoint unless i'm within 20ft on my error.

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Depends on your error positioning when you set your waypoint. If you set a waypoint and your gps has low satelite at the time, you could be off by 15 to 300ft.

Right on. I wish more people would understand that you need to check your error reading on these things to know how good your actual position is.

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OK, I follow the 'error positioning' reasoning, then what does Lowrance's MAP FIX function attempt to correct? Let's say you enter as a waypoint the RED/GREEN buoy's at Garrison Access on MilleLacs but they aren't 'On the Money' when returning; that's due to satellite error positioning at time of departing and nothing can be done to 'tweek' it? All new to me, so bear with me. Locomotiveman

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Right on. I wish more people would understand that you need to check your error reading on these things to know how good your actual position is.

how do i check this on my graph? i have a hummingbird 595c i believe

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GREG52 or? After digging into 'PositionError' more it seems that a coupla more things are at work besides 'Satellite acquisition'. Independent Lab test article showed each GPS unit can be different accuracy-wise. Yours might be 'On the money'...the next one down the assembly line...not so good. Luck of the draw there, huh? Plus Lowrance uses different mathematical algorithms than Garmin to decipher the signal and put it into a readable display. Then it just may be the Lakemaster mapping is off a tad. Add it all up and our Fishfinders are not as accurate as Military spec units...so if it's not your day...yours might be off and the boat next to you might be more accurate. Locomotiveman

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I figure that if I am so dependent on the accuracy of my GPS when fishing, then I'm not fishing for the right reasons. A GPS is a tool that can help you relocate a particular structure once you find it the first time. So what if it's a hair off. Name one freshwater fish that stays in one place long enough to matter.

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Agreed..for fishing who cares if it's off.. BUT getting back to the dock if it gets stormy/foggy on Vermillion or Winnie etc. is more my concern. Fished BayDe Noc til 11pm last Fall and the boat's GPS put us 'between the buoy's' perfectly when coming home between the gill net waypoints and rip-rap boulders. Nice. Locomotiveman

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Map Fix is a nutshell is averaging the location to the numbers...it's best guess fixing them permanently to a know point on the map. So despite satellite acquisition complications the point on the map will be the same despite wondering reception.

Garmin has this too, just calls it averaging to keep it simple. In Garmins situation it will take many many sample readings and once you see it at the best accuracy you can live with, just hit set.

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