Calibrating GPS

[Jeffry Skidmore]

I checked search first, and couldn't find the answer I wanted.



Do you have to calibrate/is there a way to calibrate a GPS system? Sometimes it seems that waypoints we set are a little off of the mark. We use the zoom in feature right to the max when returning, but sometimes the structure marked doesn't seem to be where we marked it. I know that current erodes structure and can move it, but rocks?

 

[Jeffry Skidmore]

Am I asking too much from the GPS system?

 

[Jim B]

Well GPS will get you close but its far from perfect. There are a millions reasons it can be a little off and it can be off anywhere from just a few feet to many yards off in any direction. The diagnostic page on the GPS should tell you the average position error.



Mine tends ro run at about 8 feet off all the time. It gets me close enough but its never going to put me directly on a small object.

 

[Mini]

Turn on your overlay for "Estimated Position Error" (Lowarnce). It may explain a few things. They are far from perfect but with a 4000 antenna and WAAS enabled my EPE is clost to 11 feet most of the time...

 

[Jim B]

My setup is simiar to Mini's, the only difference is i have humminbird(not that it makes much of one, they work about the same) I have the 16 channel pucks and i also have it setup for the "enhanced refresh rate"(i see no difference with the 4x rate btw, not sure it was worth the effort to cable it) but i would expect what he and i are seeing as average for any 16 channel unit with WAAS turned on and a good signal.



Back in the day before WAAS my Garmin ran ~30' EPE and it was close enough for what i needed.

 

[Marty Klein]

Well, if you are expecting current civilian GPS technology to keep your big motor from striking that rock in your path, I recommend you make sure your insurance is adequate and paid up to date.

 

[TOMMY RICH]

That's why I'll never understand guys running at night on Dale Hollow at WOT and depending upon that GPS....Seriously?:wacko:

 

[Jeffry Skidmore]

No MK, wasn't counting on that. Just wondering how accurate I could expect out of a HB. Just seemed like after marking some structure (to fish, not avoid), it wasn't alsways where I thought it should have been.



Thanks guys, for the input.

 

[Humminbird Greg]

JSkid,

There are many factors that can affect how accurate the waypoints we mark are. Some we cannot help (solar flares, accuracy of the civilian GPS signal, available satellites,

 

[Marty Klein]

That's good enough CEP, but not good enough to bet the lower unit on ...

 

[Jeffry Skidmore]

Thank you Greg. Now that is what I called an explanation. We don't use the waypoints to mark rocks, logs, etc. that we may want to avoid while running WFO, we use it to mark structure we have found to be productive in the past. Typically, we approach at idle speed (from a distance of 100meters or more), and use the zoom feature to pinpoint as we get closer. My partner has been fishing the area lakes for close to 40 yrs, knows the topography, and seldom runs faster than a reasonable cruise, so it's unlikely that we'll hit any permenant structure. I understand that evryone runs the risk of hitting a floating or semi submerged obstacle that happens to get carried into the current; hopefully that won't happen.

 

[TOMMY RICH]

Those guys can run all they want of a night @ WOT....just not me:huh:

 

[Jeffry Skidmore]

I'm with you Tee. We've seen some running WFO over bars that are three feet; not me either. Last spring we saw one who had beached on a bar in the middle of the bay he didn't know was ther during the drawdown. Don't know how much damage he incurred, but he did have to call the boat tow truck.:wacko:

 

[TOMMY RICH]

I agree...GPS will show most everything EXCEPT, floating logs, submerged rocks and possible dead bodies

 

[Greg Meyer]

Mr. Walters.... Fantastic answer... Because, after all these years of using (first) LORAN and now GPS I never gave one wit of thought to the distance between the location of the antenna and my transducer... I ran out a minute ago and measured 9.5 feet. Now when I am looking for the "top" of a rock pile that is 10-15' wide that is over 50% of the distance. Depending on when I punch in the waypoint and my direction/orientation to that rockpile... I "get it" now... I feel like an idiot (but then there is good reasons for that regardless). I WILL be moving my antenna. Thanks... If I take out even some of that 9.5' of built in error for the future....



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