Got my new Lowrance H2O GPS and gave it a try this weekend on Belton. I was really impressed, but I down loaded an "enhanced map" of Belton from the Lowrance website and some of the humps that show on the down loaded map I can't find when I am on the water.

Case in point; The GPS map showed a hump in 49 feet of water that comes up to 29 feet, but when I get to the spot on the GPS I can't find it. This happened on 3 different humps I was trying to locate. I pulled out the "Hot Spot" paper map and it did not show the humps on it. I did a grid search using my Eagle Fish Mark 480, but was still unable to locate the humps. I did locate one hump that was on the paper map and also on the down loaded map.

I can only conclude that the humps don't exist or the down loaded GPS map is incorrect.

Anyone else had this problem? I am doing something wrong?

Please help.

Cary

One more time guys....HELP!

I would check with "Hot Spot" (which you did) and even Topozone.com. If they don't show it, then there is a good chance that hump does not exist. I have had a similar problem. Basically, if you don't see fish or structure, you could try doing a circle pattern around the original spot.

One problem I had, was that at one point in time, Selective Availability was being utilized which put my unit off by many yards when I came too close to a selected/protected structure (i.e. Dam).

Good luck

I work for various pipeline companies as a mapper and surveyor. so I think I can offer a lil bit of input here. IF you've got your equipment installed correctly and are interpreting it correctly, then Trust it. The Map that you DL'd is likely produced by a 3rd party (contracted) GIS firm. therefore the data could be a lil bit shabby in some places. it passes thru lots of hands before it ends up on your sonar unit. so theres lots of chances for some of that data to get whacked. Definately NOT Gospel Truth.. but it still helps.
Topozone= USGS derived. lots of checks go into this stuff. its a High standards outfit so you get trustworthy (all be it sometimes out of date) data. same w/ hotspots. Bottom line, if your sonar agrees w/ the good data- thats what I'd go with.

guy from sealy,

I am curious how they plot underwater depths? Any idea?

same way you do.. except they use more expensive gear :p - and the data is recorded. The sonar derived distance to the bottom is associated w/ the x,y coordiantes so you get an x,y,z - everything is on a grid- alllll coordinate geometry. a LOT of math.. thats it in a nutshell

Thanks guys for the insight.

With the exception of trying to locate these few humps the down loaded map has be very accurate. The counture lines on the GPS match up with what the depth finder is showing at what ever my current position was.

I was just hoping to locate a few of these "mystical humps" that I read about here on the forum where guys catch lots of whites and hybrids. I guess I will just keep looking.

As soon as I find them I will be sure to send all of the coordinates!

Cary

Quack, another thing to look for is the Map
Datum Reference. Somewhere on your map it should
say something like NAD27 or WGS84. The DATUM is
a starting point that the coords are based on.
So if your map coords are based on NAD27, but your GPS is set to locate based on WGS84 data
the 2 differences can be several hundred yards
apart. I found this out when trying to locate
brushpiles using my Martins Map coords and finding my GPS directing me several hundred yards
onto the woods (my GPS came set at WGS84 Datum).
After I reset it, Its dead on target!
GoodLuck, Sniper

Sniper,

After looking a the Hot Spot map I have for Belton it is set for NAD27 and my GPS is set for WGS84, so that looks like an easy fix. Thanks for the help there.

But what about the "enhanced maps" that I down loaded for the Lowrance website. Should they not be set up on the WGS84, just like the Lowrance GPS I am using? I looked on the website, but could find no information about what DATUM the "enhanced maps" were using.

Again, thanks for the help.

Cary

If my gps is set at NAD27 and I change it to WGS84, will this affect my previously saved coordinates?? I probably have the same paper map as Quack and would like to try it out this weekend. Thanks in advance...

NAD Coordinates = Stateplane Coordinates - Texas is seperated into 5 Zones - Belton being in the central zone. the numbers 27 83 were the years that the coordinate syss.. were updated and changed - similar grids.

WGS84 Coordinates= Latitude and Longitude-this is the world grid. Your GPS SHOULD be able to READ the stateplane stuff while displaying the WGS84 data.


Sniper is right (pretty much) - your GPS unit has to be in the same system... without being to preachy - just make sure your numbers match.

On the other hand, If hotspots is in nad27, then you'll have to enter those coordinates in that system because 27 coords arent equal to 83 coords.
naaa.. its not complicated lol