Thread: GPS position errors........

Originally Posted by KARL

I'm not that savvy on GPS operations...was wondering if someone could help me with a problem I've got....
I have Navionics hotmaps loaded on a Lowrance LCX-19c...went to a bridge on the map... sitting under bridge the gps told me I was 153 ft west of bridge....Is there a way of entering a offset into gps to correct position error???? The reason I ask is I have some brushpile waypoints loaded onto map and when i pull up on WP icon no brushpile....tried several different WP...153ft is a lot of water to try and find pile by searching in circles or zig-zag.....any and all help would be greatly appreaciated.....looked in my GPS manual and don't see anything close to a offset correction......they have a term called Map Fix...but it's for finding a specific position from co-ordinates on a paper map.....don't have paper copy of all the brush co-ordinates.....somebody ...anybody....HELP...

Did you enter you waypoints by hand?

No...entered from file sent via e-mail..loaded on SD card...then used GPS to load to hotmaps SD

You got WGS84 map datum selected right?

I am not familiar with LCX (and I have one).

Map datum wrong or data entered in wrong position format can cause position errors.

Ima swagging.

Yeah, got the WGS84 selected......brushpiles aside.....the problem as I see it is.....that my actual position doesn't match up with the Hotmaps position...ie sitting under bridge (actual).....boat being shown 153' to the west of said bridge......I guess that's why on the hotmaps SD card package it says...."this is a fishing map not intended for use as a navigational chart. Your GPS may not show your position correctly against this fishing map because the the GPS position may be more accurate than the position of the original source data."....which in my opinion,.. sucks out loud..thats why there should be some sort of offset to correct this ....bull hockey..:D....I could live with 20' off but 153' is total crap......
Is there any program where I could load the hotmaps or a different map to a SD card put in a offset and then run off of the SD corrected card....Thanks

Originally Posted by KARL

Yeah, got the WGS84 selected......brushpiles aside.....the problem as I see it is.....that my actual position doesn't match up with the Hotmaps position...ie sitting under bridge (actual).....boat being shown 153' to the west of said bridge......I guess that's why on the hotmaps SD card package it says...."this is a fishing map not intended for use as a navigational chart. Your GPS may not show your position correctly against this fishing map because the the GPS position may be more accurate than the position of the original source data."....which in my opinion,.. sucks out loud..thats why there should be some sort of offset to correct this ....bull hockey..:D....I could live with 20' off but 153' is total crap......
Is there any program where I could load the hotmaps or a different map to a SD card put in a offset and then run off of the SD corrected card....Thanks

Ok. My HB NVB is 100 ft or so off in some locations. I fish dry land sometimes and some imaginary channels.:rolleyes:

HB has an internal map calibrate function. I tried it. Didn't do chit.

I feel your pain. Prob go back a few years in archives and read my "bitching" about the NVB maps. The Premium maps seem to be more accurate.

I don't know about Navionics maps or the ability to calibrate them.

Only thing I would know to try, for simplicity, and it may not be a consistent offset distance/bearing across all points. Matter of fact, I would doubt it given the accuracy of these units anyway. Anyhow, find a spot/brushpile and compare your actual coords to your assumed coords. That is your offset distance/direction. I know it would be a pain, but to be relatively accurate, buoy at your waypoint and a buoy on the brush, go to your waypoint and shoot your brushpile to get your direction with compass. The next brush pile you want to fish, go to your waypoint, shoot your bearing and go however far you need to. You'll be able to figure out how consistent your offset is. If it's fairly consistent, I would use a survey program to offset your waypoints, all of them. The new coords would/should be on your brush. Long way around I know, but it can be done. You can take your new points and load them into your unit. This won't fix your position to map problem, but it should get you a lot closer to your brush.

If you find a brushpile and mark it on the water you will have no trouble getting within 15' of it-with practice on driving to the waypoint and paying close attention to distance to go you will get closer than that.

I had the exact same issue when I tried to enter coordinates into my Lowrace HD from a store bought lake map.
What I found was the info on the maps ... chose Lat/Long and then mins and seconds... and I can't remember what the default setting on the unit was... but it was different. Maybe degrees or something.
Check to see if the info your putting in from a lake map... is the same as what's actually on the map. Once I figured that out... it worked great.
Good luck