Chart display not aligned with location

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Chart display not aligned with location

Postby okazaco » Tue May 07, 2019 1:29 pm

I noticed on two occasions that the chart is showing my location as being up out of the water, an error of about 30’. I noticed this both at Camanche as well as the North Delta. Is there a way to re-sync the chart overlay with my HDS Gen 3 unit?
Ranger 520 / Yamaha HPDI
Wellcraft V20 / Evinrude XP

Ken Sauret
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Re: Chart display not aligned with location

Postby Ken Sauret » Wed May 08, 2019 6:46 am

The preloaded chart data in the Lowrance units are "general" representations of the body of water you are on. This is why the screen that you "Accept" when the unit boots up indicates that you agree not to use this unit for navigation. You must always look in front of you while navigating any body of water so you know you are safely in the navigable water. The representation of the water and land areas on any chart data really don't matter in reality. They are there for you convenience really. You could just have a plain background and if you set a waypoint the exact position on the face of the earth is marked. It doesn't matter what the map data says. Next year you could go to that waypoint and be on the same location on that body of water and the chart data would still be a plain background. The map data is there to help you visualize where you are. The C Map cards or the other 3rd party map cards you can purchase will have more details on them to help you find specific structure areas like points, steep or flat banks and so on. They have an additional cost to them because that company has gone out and surveyed the body of water in most cases and has better map detail than what an electronics company can preload into a unit and still make money to stay in business.

Another issue beyond any electronics company is the random accuracy of the GPS on any day. The sun spews out tons of electrons into space that bombard our atmosphere and the more electrons in our atmosphere the less accurate the GPS is. To find this error on any day, hit your power key and in the dialog box that comes up hit Settings. In settings hit system. Go down that dialog box and hit Satellites. Find EPE in that dialog box. This will tell you how far off the GPS is at that moment. EPE stands for "Estimated Position Error". This is how many feet the waypoint you may set is away from the actual square foot the structure item you are marking could be.
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