LMS 522c IGPS has me on land. - Bass Fishing Forums - The Bassholes
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Old 02-27-2008, 06:53 AM   #1 (permalink)
 
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Default LMS 522c IGPS has me on land.

I am running a LMS 522cIGPS with a Navtronics 2006 map. I have already made sure I have my Deg, min, sec settings for both sides, but to no avail.
When I was at the Expo at the Classic, I went to the Loweance booth and spoke with some goob, who didnt really have an answer except "Its probably the map"
Its hard for me to believe that that navtronics map would have me 30 yards away from where I am.
Lil help here? :aml-lures:
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Old 02-27-2008, 07:42 AM   #2 (permalink)
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Default Re: LMS 522c IGPS has me on land.

How do you have it mounted? That model has to be set with top up to the sky with nothing blocking a signal. It won't work right mounted flush in a console panel, or laid on its back on the bow, or having some part of the boat hanging over it. Anytime you think the position is way off PAGE over to the satellite status page. If you are in 3-D mode your unit is locked to a true reading, but can still be off due to factors like atmospheric interference, reflections, radar. That's why they put an estimated error figure on the screen. Chance are you would have found a 30 yard estimated error. Whatever error you note there, plus which cardinal direction the error is in helps you interpolate subsequent positions. In that case you would mentally note whatever the screen shows has you 30 yards farther east, for instance, that hour until signals improve.

If the mode was 2-D you were using less than 3 healthy-signal satellites.

Jim
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Old 02-27-2008, 09:20 AM   #3 (permalink)
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Default Re: LMS 522c IGPS has me on land.

I have found the Navionics card to be off on only one occasion- you can easily determine this by going under Map Data and changing to the built in Lowrance map. If it is accurate, then the Navionics map is the issue. If it is off, check your GPS signal, mount, etc., as described above.
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Old 02-27-2008, 09:48 AM   #4 (permalink)
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Default Re: LMS 522c IGPS has me on land.

Not to make a big deal out of it, but according to government experts wondering the same about accuracy of e-maps on the market, cartographers say it is practically impossible for something like a Lowrance or Navionics map to be "inaccurate". They either work or don't at all. Each copy of a master map has to match a byte count file to pass inspection for sale. Each map on a memory card has built-in georeferenced points established at verified land-surveyed positions. They are no different than any other computer file that if corrupted, won't work right at all, and usually won't even load. This came up when the Corps of Engineers began investing a huge sum of funds into GPS mapping,. Engineers didn't want to just accept the new technology maps, wanting to keep the old survey teams around since those hired engineers. The survey teams lost, the e-maps won. Not once was any e-map found to be off more than the manufacturer's claims.

Any problem with reading an e-map has to be the quality of GPS signals, the equipment reading it, or user error. If your e-map is bad it won't load because of a small file that tells it not to load if even one byte is out of place. The program your computer is using to bring you Windows, or the internet, is the same. One byte off and you get nothing. It is all or none, else nobody would know there is a problem until some terrible maybe life-threatening error occurs.

Position of the receiver is usually the main culprit. The antenna has to have a completely free view of the sky to be considered reliable. Any reduction of signal quality degrades output quality. Your GPS unit always offers an estimate of degradation. Units with built in antenna are meant to be used in an upright position, freely standing by itself and not blocked even by a human body.

What's happening in the upper atmosphere, as affected by sun spots and other anomalies, comes next. Some of those factors are known to the overall GPS system and your unit can download corrections. That's how it derives an estimate of error. Satellites transmit information send up by ground stations that pass on atmospheric data. Health of a satellite is also known and information about it is sent to your unit. Your unit might be seeing 8 satellites at once, but can only rely on 4 of them. As long as you have three or more you can use the positions with some good accuracy within the est. error range.

Next comes electrical issues, such as low voltage and electrical noise, in order of causes of problems.

The settings for GPS are mostly default driven and not likely to ever be changed, but sometimes folks tinker with those not knowing the results. You can always reset to factory default and recover the proper North American settings that applied at the Tulsa factory.

Jim
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Old 02-27-2008, 09:57 AM   #5 (permalink)
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Default Re: LMS 522c IGPS has me on land.

Jim, You never fail to impress me with your in-depth knowledge of GPS's.
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Old 02-27-2008, 10:05 AM   #6 (permalink)
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Default Re: LMS 522c IGPS has me on land.

Your past tax dollars at work in retirement The Corps sent me to every known GPS and sonar school for a decade so I could promote their use among other government workers all over the USA. We produced a video series on it that is still in circulation. I wish I had a copy to post here, but can't own one, but still have all my certificates.

Get all you can out of me before I begin drooling and telling the same stories over & over when takes over. We need to somehow have a crash course class for members at some location. I've done that on Lake Ouachita several times using a party barge with equipment installed, where a group can gather around to get hands on experience, but only for government employees. If we could get Doc Samson and JEVSkeeter (Humminbird demo guy) in on something like that we'd really have something to hoot about. One-hour shock lessons work fine, as I've gone out on Ouachita with many pros, mostly guides with their first unit, and amateurs alike over the years to get them going.

Jim
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Old 02-27-2008, 09:53 PM   #7 (permalink)
 
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Default Re: LMS 522c IGPS has me on land.

Thanks for the info guys.
I have my unit mounted on the gunwale on a ram mount. The antenia is straight up.
I havent tried it with just the Lowerance map.
I have checked the satilites and there are several. Its aggravating. I thought gps was supposed to be with in 3 meters.
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Old 02-28-2008, 06:39 AM   #8 (permalink)
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Default Re: LMS 522c IGPS has me on land.

There usually are "several" satellites being detected, but fewer are showing health. You need 3 healthy ones without interruption to maintain an accurate position.

You should expect accuracy within 3 meters. Our level of GPS is capable of positioning within one meter under ideal conditions, when combined with WAAS. When you see the estimated accuracy gets more than you allow you know to figure in some error, both in feet and direction.

A way to sharply reduce error is to average waypoints. When you press the WPT key a drop down menu appears to give you some options, like naming the point, and averaging position. The unit collect a point a second, then averages those clustered around a central position, ignoring wild positions not related to the interior cluster. It's like patterning a shotgun. Some pellets will be all over the target sometimes, but many will be clustered. The software looks at the points within a circle made by the strongest points. The longer you permit averaging, the greater the accuracy.

Next time you find your position showing on land, set a waypoint where you are, letting it average a minute. When done look at the waypoint on the map. That will be your best position available, which ought to be much closer to where you figure you are on the map. This is why they put the disclaimer on the opening screen, never to rely solely on GPS for navigation, but to use all your navigation skills alongside GPS.

Once a year I like to test my GPS by setting the boat up so the antenna is over a survey monument I have coordinates for. It is supposed to be accurate to within 1/100 foot. Well, I can't get the antenna positioned very accurately, maybe within a foot in all directions. I let it sit collecting 5 minutes in 3D. So far the averaged position has not been more than 3 feet off. I use a surveyor's calculator to measure the difference between coordinates.

Jim
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Old 02-28-2008, 09:09 AM   #9 (permalink)
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Default Re: LMS 522c IGPS has me on land.

I have been on land a few times while boating and I have seen both map problems and GPS problems. The post on switching from the Navionics to the Lowrance background map to check accuracy is a great idea. The mapping companies want you to notify them if you have this and it is not related to your GPS error. They can then make corrections in their new chips. I have a GlobalMap 3300 in my pickup with a camper that extends over the hood and it will block the satellites rarely and then it shows me driving away from the road. I have the EPE (estimated position error) on the overlay and it will be 300 ft until a new satellite is used and bingo I am back on the road.
Another error I had was when I installed the LowranceNet. I had 2 separate GPS units not connected by the LowranceNet. I hooked up a LowranceNet with my new units and in doing so I powered the LowranceNet twice by mistake. My GPS was crazy until I solved the mystery.
Information from Lowrance: Lowrance EPE is calculated from all the satellites in view but your actual position is calculated by the best satellites in view. If the EPE is high you can still be accurate but if high be wary. If low you are safe. For example: a number of 60 ft doesn’t mean you are not within 20 ft of your spot.
I think Jim has said this before but the best way to place the antenna is to have the unit on and the EPE on the screen and move the antenna around to find the best place before you permanently mount it. It is not perfect because the satellites change positions in the sky but it works well. You can even see how the EPE is affected by your body!
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Old 02-28-2008, 10:13 AM   #10 (permalink)
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Default Re: LMS 522c IGPS has me on land.

Jim,

I would think with your GPS and overall sonar knowledge that you could land a nice consulting type job with Lowrance or Garmin or Humminbird etc.

I know you are retired but maybe they have a position where you could work from home answering people's concerns?

Thanks for helping us all out.
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