Fishfinder/GPS discrepencies...

Discussion in 'LOCAL OHIO TALK' started by Salmonid, Dec 2, 2009.

  1. Salmonid

    Salmonid New Member

    Messages:
    1,833
    State:
    SW Ohio
    Any of you tech guys out there know about how GPS coordinates work, can you tell me why every time at the river, when I mark spots ( waypoints) and the GPS shows my trail when running, why there is always some discrepencies and a bigger then Id like margin of error with them, I have a rather expensive GPS Eagle unit ($600-700 range) and noticed that sometimes my waypoints are off sometimes by a few feet and sometimes about 25-30 feet!! ( compared to fixed objects on shore/ etc) I dont mind being off a bit but at least be off a little bit every time or at least in the same direction, I sent Eagle/Lowrance an email a few days ago but never heard back from them. Anyone know what the standard deviation of error is on these units?? Just curious I suppose.

    Are the handhelds any better??

    Should be a good discussion here since the temps are falling and the next week will be snowy, sleety and lows below freezing and not much fishing gonna be happening:crazy:

    Salmonid
     
    Last edited: Dec 2, 2009
  2. waynesburgjay

    waynesburgjay New Member

    Messages:
    1,960
    State:
    Pennsylvan
    I don't think there made to be exact, but you should be within 50 ft.
    I guess they don't want anybody to strap a missile on one and be able to
    pick off things with any accuracy. That's my story and I'm sticking with it.
     

  3. Salmonid

    Salmonid New Member

    Messages:
    1,833
    State:
    SW Ohio
    I have heard the handheld units are supposed to be around 30 ft for mediocre units and 12-15 ft for the higher end units but never have heard how accurate the Fish finder versions are. I just know its frustrating running down the river and seeing 50 lines from the ramp starting point and not 2 of them are in the same exact spot, not to mention the Navionics map chip shows half the time, i am running on dry land......I really don t think the entire Ohio river has moved that far since they did the mapping of it for the software... Kinda frustrating since I tend to mark not only humps/ledges but also large rocks/concrete and trees that are just under the water with waypoints and need to remember that its not that accurate and I should always steer way clear of these items.
    Salmonid
     
  4. Swampfox.

    Swampfox. New Member

    Messages:
    1,182
    State:
    Louisiana
    Bluejay has some knowledge on this, i'll pm him and put him on this thread.
     
  5. bluejay

    bluejay Well-Known Member

    Messages:
    8,494
    State:
    Napoleon, Mo.
    I'm no expert on this Matt. I believe it has to do with satilite strength. The same Gps will be off 5' one day and 25' offf the next. I have seen this with handheld and the Lawerence on my boat. I have not seen a higher price unit that will not show you on dry ground also at times.
    Very interesting post. I will follow it. Thanks for your kudos Matt.
     
  6. plainsman

    plainsman New Member Supporting Member

    Messages:
    7,187
    State:
    minnesota
    I"m not sure about boat mounted, but my handheld GPS will get with in 9 ft, other times its not so good. It all depends on which satellites and how many the thing is tracking. The longer I wait for it to track satellites the smaller the margin for error. Sometimes its not as accurate as others but I think that is due to different satelittes and their locations.
     
  7. tbull

    tbull New Member

    Messages:
    3,318
    State:
    SW Ohio
    Mark I am pretty sure its a security deal..
     
  8. Salmonid

    Salmonid New Member

    Messages:
    1,833
    State:
    SW Ohio
    Tbull, yeah, I know its military technology that was dumbed down for public consumption but damn, at least it could be off the same amount every day....:wink:

    Hopefully Ill get my answer back from Eagle/Lowrane as to teh error of margin the typical unit has on the water and if the water has any effect on it.

    Salmonid
     
  9. catcrazed

    catcrazed New Member

    Messages:
    575
    State:
    ohio
    I actually was on a crappie fishing website last year and this came up. There is a humminbird tech guy on there all the time. Joby with Humminbird said that it is is definetly a security thing!! Something that he said that blew me away was that the farm type gps's for tractors are a lot more on the money and I know that for a fact now that Ive talked to some of the farmers. They are within a foot all the time. People use these for spraying and what not while farming.
     
  10. centexcop

    centexcop New Member

    Messages:
    3,013
    State:
    Texas
    I agree with the security issues, no GPS is going to be right on. But I think Bluejay has this one nailed down. I've noticed on some of my hand units that they are sometimes a little off (more than I think they should be). I'll check the satellite strengths and every time it's off, I don't have the strength or I don't have as many satellites that normally show up.

    Does your unit have an external antenna? When you find that it might be off, turn off the unit and let it get another fix on the satellites.
     
  11. Tool958

    Tool958 New Member

    Messages:
    508
    State:
    Illinois
    I seem to remember someone on here having the problem of his GPS/fishfinder, I think it was a Lowrance HDS, being off quite a bit. He went to Lowrance's website and downloaded the latest updates and cured the problem. Don't know whether this will help, but it's worth a shot.
     
  12. tbird

    tbird Member

    Messages:
    266
    State:
    IN
    Does your receiver have WAAS capability? If you have a satellite page see that you are tracking 3 birds and have a WAAS connection to get best accuracy. This will be the most accurate even better than farmers used to subscribe to get.
     
  13. Kat-addict

    Kat-addict New Member

    Messages:
    114
    State:
    ohio
    Mark: Accuracy on all recreation type gps units is 30'. Maybe real close one time and 30' off the next. Farm type gps units for guidance and spraying = 6 inches. I have one that I use for guidance when I spray and it will put ya pretty much right on a spot but basically only carrys one waypoint....the last place you marked. Military gps....spot on !

    I am thinking about putting my spraying lightbar on our boat...lol.
     
  14. skippi2use

    skippi2use New Member

    Messages:
    866
    State:
    Indiana
    Mine seems to be pretty accurate most of the time. I notice that it is not doing so well I will check the satalites that I am locked on to and I will only be locked on to 1 or 2 satalites. it is sopposed to be locked onto 3 satalites for accuracy up to 9' I believe. The other thing that seems to really affect it is low voltage. Dont know if you can check to see what satalites you are on or not but might be worth a shot. Could be an antena problem as well.
     
  15. Salmonid

    Salmonid New Member

    Messages:
    1,833
    State:
    SW Ohio
    Shane, yeah, I figure its an internal antennae and its constantly beeping saying, "Position Aquired" then a few seconds later will say "Position Lost" so I got a Raam mount which sticks it out a few inches from the neathside of the windshield and that seems to really help me hold a signal . The unit is a WAAS system and it does have a screen to show satellite strength, I just have to figure out how to find it....These new fangled units are jst a bit too complex sometimes....:eek:oooh:

    Thanks for everyones input, I am still waiting for a response from Lowrance....

    Salmonid
     
  16. tbird

    tbird Member

    Messages:
    266
    State:
    IN
  17. skippi2use

    skippi2use New Member

    Messages:
    866
    State:
    Indiana
    I have a lowrance hd, It seems to be right on the money it also has an internal gps that sets under the windshield on the boat. I have had no problems. I spent about a week going over the book before I ever put it on the boat. REALLY helped me out because that thing does a ton of stuff that my hummingbird could not do. Here is a link that I found gives a little of the history and accuracy.
    http://www.lowrance.com/Support/Tips-and-Tutorials/GPS-Tutorial/ They have all the tutorials on the lowrance web site, I would think the eagle would be about the same.
     
  18. metalman

    metalman Well-Known Member

    Messages:
    3,447
    State:
    IN
    Name:
    Winston
    I think a lot of it has to do with the installation, software and the antenna as well as the particular error factor that the military choose on a given day. I would think though with as much as the military must be depending on it these days the and the fact that where they are operating is probably not DGPS or WAAS friendy, the degree of error must be turned way down, if on at all.

    I have an HB 997SI unit with built in maps. Sometimes it will show me on the map that I am on dry land when I am close to the shore but, on the same day, if I put in the way point for the ramp it will take me right to it and count down to the foot as the keel hits the dirt.
    I don't trust the map entirely but the navigation, way points and distances seem very reliable...W
     
  19. GaryF

    GaryF New Member

    Messages:
    3,649
    State:
    O.P., KS
    Mine is a Humminbird 797, and like Winston said, the navigation and waypoints seem pretty solid. My trails are just about on top of each other, and some of the waypoints are marking hazards that I have to pass close to to get up the river. I'm able to use gps to cruise on by these and stay on a safe track.

    There is a "gps diagnostics" page on this unit that reports margin of error, among other things, and it will typically report between 9 and 27 feet. But from my own observations against fixed waypoints, the actual error is much less than that.
     
  20. catwhisper

    catwhisper New Member

    Messages:
    456
    State:
    georgia
    can you buy the military GPS's? and are they more accurate?