GPS Calibration

[Double A]

I just installed a Lowrance 522C. When I tried it out this weekend I noticed that the maps were 100-200 feet off. I have the Navionics Hot Spots Map to give more definition but the map is not even close to being on.

Is there some calibration required for a new GPS?

[RK]

Hiya -

Look in your GPS data menu for the Position Error reading. That can tell you how close the margin of error in your position fix is. Some days are better than others for getting a good fix. How close your GPS module is to your head unit can affect your PE too. The closer your receiver is to the head unit, the greater the PE usually.

Likely as not though, it's the map itself that's the issue. A lot of the chips use the basic DNR map unless you're on a lake the company itself has re-surveyed. Some of the DNR maps are wildly inaccurate (consider that many of them were made years and years ago with not much more than dead reckoning and visual triangulation). Where you are in relation to the actual structure vs where the structure is shown to be on the map is only as accurate as the map is, satellites notwithstanding.

Sometimes too even if it's a more recent lake survey the map chip might be off a tiny bit here and there - just a little distortion in the plot can put you off my well over 200 feet. When the first Lake of the Woods chips came out, they were almost comical they were so erratic. In one place they'd be spot on. In another they'd show you 200 yards up on shore... We sent a lot of emails to Navionics showing them the trouble spots, and they gradually re-adjusted the maps to correct the distortions... Although they still show one island that just flat isn't there...

Hope this helps...

Cheers,

Rob Kimm

[Fishin' Addict]

No map will ever be accurate enough for navigation without preset safe routes you can run. Don't think for a second that you could navigate off of them - especially the navionics maps. The maps are essentially just "ball park estimates" that get you near, in some cases, or right on top of structure, in other cases. As the previous poster said the location of structure is based on the DNR long/lat legend on every hard copy map - heck you can scan them in and do the same thing if you know how to use the software.

The most accurate maps that I would say are "dead accurate" are the "high resolution" maps made by Lakemaster for Otter Tail, Winnibigoshish, Cass, Lake of the Woods, and Vermillion as well as a bunch in the Brainerd area. But still I wouldn't navigate off of them.

Just remember the maps are a ball park estimate and getting you to withing a 100-200' of certain structure is better than having to search for a small hump in the middle of a 4000 acre lake.

[Double A]

RK, FA:

Thanks for the posts. the 522C has a built-in GPS so I'll check the accuracy. I will have to do some "fast surveying" on my own to find the humps.

Even though the map shows I'm running my boat across an Island I'll just have to be sure that when I fish the hard water I don't drill my hole into the dirt.

A friend of mine has the Lakemaster Minnesota maps and is very pleased with that set. Are they better than my Navionics Hot Spots North Maps?

Thanks again.