Author Topic: GPS Position accuracy  (Read 16861 times)

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Offline Kenosha

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GPS Position accuracy
« on: October 19, 2010, 06:51:20 AM »
IF I mark a position when I am tided up to a stump, and return after I move the boat several hundred yards then return to the same stump within a few minutes the distance to go shows 12 to 14 feet. I have the latest upgrade V4.970 and GPS error is 2 to 3 feet. Is there any way to set it to show 0' for the spot I mark?
I would like it be 0 (+/_ 2 to 3 feet). Is that possible ?


Offline FuzzyGrub

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Re: GPS Position accuracy
« Reply #1 on: October 19, 2010, 07:31:57 AM »
Well, that is tighter than the gps accuracy provided, but you may be able to improve on what you have.  Where is your gps receiver, transducer, and unit mounted? 
If it bends my rod, I'm a happy fisherman.

JohnS

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Offline sonar2000

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Re: GPS Position accuracy
« Reply #2 on: October 19, 2010, 08:15:20 AM »
If you are tying to a stump then also tie a marker (red, yellow, white or some color tape) then you can see the stump again on return. Just kidding but it would work
GPS accuracy from any unit is never a "0" but only very close. Use the gps to get close and then use sonar to find the exact spot (when it is undewater).
Sonar and gps work very well together.
Also gps does not work well if you are not moving or at the least a very small motion. You need to be in some form of navigation (motion) to produce the accurate position display.
If the area is submerged I would use sonar to get back on the spot.
Chuck

Offline Kenosha

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Re: GPS Position accuracy
« Reply #3 on: October 21, 2010, 07:17:47 AM »
I tied a red marker on the stump and it still is 12 to 14 ft. in the DTG window.
HA. When I used a Loran unit its accuracy was much better. But the GPS is what we have now and it works OK.

Offline Humminbird_Greg

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Re: GPS Position accuracy
« Reply #4 on: October 21, 2010, 11:55:51 AM »
Kenosha,
Where is the GPS Receiver located on your boat?
When you mark the position of the stump, is the GPS Receiver right next to the stump?

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline jerry b

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Re: GPS Position accuracy
« Reply #5 on: October 21, 2010, 04:19:02 PM »
Greg, let me add another question to the mix.  My puck is located next to my 898 on the console and reads fine.   Today, while in the Bird's Eye View, I'm going south in a cove and the red boat in the unit is going toward the stearn, in other words opposite the direction I'm travelling.  Is this right?  If not, how do I go about correcting it?

A lot of good info. is put out on this site.  Thanks

Wayne P.

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Re: GPS Position accuracy
« Reply #6 on: October 21, 2010, 04:29:05 PM »
That is because you have your unit set for North Up instead of Course Up.
Review your operating instructions.


Offline jerry b

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Re: GPS Position accuracy
« Reply #7 on: October 21, 2010, 04:57:09 PM »
Thank U Waype for the quick response.  I have downloaded & printed the manuel but can not locate how to change to 'course up'.  Any help?

Offline Humminbird_Greg

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Re: GPS Position accuracy
« Reply #8 on: October 22, 2010, 11:00:37 AM »
jerryb,
The menu that Wayne P. posted about is the “Chart Orientation” and it can be found under the “Nav” menu tab in the main menu system.

I don’t know of a menu setting that would cause this as the boat should always be pointed towards the top of the display.  The only way I know of to make this happen would be to use the cursor to rotate the boat in the opposite direction but this would get reset whenever you power the unit off or go away from the Bird’s Eye View.  Could you have just used the cursor (4-arrow key) and rotated the View?

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline Kenosha

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Re: GPS Position accuracy
« Reply #9 on: October 25, 2010, 08:42:30 AM »
My GPS puck is located on the rear port side on a fd 80 14' alumacraft  boat the receiver is mounted on the port side of the rear seat 4' from the puck. The rear of the boat is about 2' from the stump same spot when it was marked.

Offline Humminbird_Greg

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Re: GPS Position accuracy
« Reply #10 on: October 25, 2010, 01:35:42 PM »
Kenosha,
That may be about right.  Your 898 should be using the GR50 GPS Receiver which we have measured to have a 13 foot accuracy rating 95% of the time (5 foot 50% of the time).  Add the additional 2 feet between the stump and the GPS Receiver when you mark it and you are within the normal parameters that we have measured.  With you being in Texas though I would expect better than that as you should have many GPS satellites to get positioning data from (including the WAAS satellites).  Try temporarily mounting the GPS Receiver on top of your motor in order to get it above most parts on your boat that can block the signals from the satellites.  Next; try marking the stump and come back to it with the stump right next to the GPS Receiver and while traveling in the same direction both when you marked it and when you returned.

Greg Walters at Humminbird
gwalters@johnsonoutdoors.com

Offline Moose1am

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Re: GPS Position accuracy
« Reply #11 on: October 31, 2010, 11:06:40 PM »
I extended my GPS AH50 puck Antenna above the deck about 2 ft high.  This gets the antenna above the motor.  My estimated Accuracy is now plus or minus 3 ft most of the time.  DPOH is below .80 now.
 
I think that the Government changed something on the GPS Satelites as the acuracy is much better this fall as compared to this spring.
Regards,

Moose1am

Offline Colt45

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Re: GPS Position accuracy
« Reply #12 on: November 01, 2010, 01:25:02 PM »
You can 'View' the 'GPS Diagnostic' screen to see satellites, signal strength, etc.  If you can't 'see' the satellite due to hills, trees, etc the accuracy will suffer.  The direction of the 'boat' icon is what the GPS thinks you are moving.  If tied to the dock the icon may move around as the GPS drifts in the acceptable error range.  If viewing the GPS Diagonistic screen watch the last digit of the coordinates to see if it changes.  A coordinate shown in Deg MM.mmm is about 6ft +/-.   A Minute (Nautical Mile) divided by 60 to 3 decimal places.  Verify also you are in 'Enhanced Mode'; ie using WAAS.  You can also try writing down the coordinates and recheck next time you go back to the stump.  I generally use my dock as a reference point.

Offline Moose1am

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Re: GPS Position accuracy
« Reply #13 on: December 01, 2010, 11:16:31 AM »
Great Advise

Reminds me that you can change the way the map coordiates are displayed to Deg Min Sec .  Would that give more precise readings that using the Decimal Deg Settings of Deg MM.mmm?

Not sure if it makes any difference but the finer the resolution that can be displayed perhaps the more accurate the readings may seem.

What about changing things to display in Ft vs Meters?  Will that increase the precision of the readings? 

I have read about how to convert from degrees to decimal deg etc.  60 mins in one deg ... 60 sec in one minute.... 60 min in an hour etc.   But it can get confusing when you try to add the decimal degs together after converting them to decical equvelents of reg angular deg.  That's going back to my HS Trig Class and that was the last semister of my HS and I was not in the mood to study at that time.  Big Mistake on my part.  I now regret not paying more attention to that math class.  Although I don't have to use Trig very often there are times when it does come in handy.

You can 'View' the 'GPS Diagnostic' screen to see satellites, signal strength, etc.  If you can't 'see' the satellite due to hills, trees, etc the accuracy will suffer.  The direction of the 'boat' icon is what the GPS thinks you are moving.  If tied to the dock the icon may move around as the GPS drifts in the acceptable error range.  If viewing the GPS Diagonistic screen watch the last digit of the coordinates to see if it changes.  A coordinate shown in Deg MM.mmm is about 6ft +/-.   A Minute (Nautical Mile) divided by 60 to 3 decimal places.  Verify also you are in 'Enhanced Mode'; ie using WAAS.  You can also try writing down the coordinates and recheck next time you go back to the stump.  I generally use my dock as a reference point.
Regards,

Moose1am

Wayne P.

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Re: GPS Position accuracy
« Reply #14 on: December 01, 2010, 12:32:06 PM »
Decimal degrees is the most accurate XX.XXXXXXXX

The last time I was at Lake Fork (May 2010) I had my 798ci SI with me to demo to a potential SI purchaser. I was getting 2 ft EPE with the unit in my lap.
All the WAAS satellites are at the equator and the further you are away from the equator, the more signal is lost due to the position from the horizon those satellites are. I regularly get 3-4 ft EPE in Virginia.

Offline FuzzyGrub

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Re: GPS Position accuracy
« Reply #15 on: December 02, 2010, 12:50:54 PM »
I regularly get 3-4 ft EPE in Virginia.

FWIW: I got some similiar EPE readings in NY while marking out some property.  Latter, when I went to the county GIS site, and used their satalite photo overlay, and picking an object I got coordinates for, found the EPE to be accurate/very close for those positions.   
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Offline Moose1am

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Re: GPS Position accuracy
« Reply #16 on: December 23, 2010, 08:15:05 AM »
This spring I was getting estimated accuracy of plus or minus 17 ft for the most part.  This fall of 2010 I was getting estimated accuracy of plus or minus 3 ft or so. 

Something changed in the GPS Satellite System.  My DCHP SP? also went down (which is good and indicated increased accuracy). 

I think that they sent up a new Satellite as in the GPS Satellite view on the UNIT I think I see more satellites showing up.  Some are duplicate WAAS satellites I think.

Anyone else noticed an increase in the Estimated Accuracy on their Humminbird units or any other gps type units?


Decimal


degrees is the most accurate XX.XXXXXXXX

The last time I was at Lake Fork (May 2010) I had my 798ci SI with me to demo to a potential SI purchaser. I was getting 2 ft EPE with the unit in my lap.
All the WAAS satellites are at the equator and the further you are away from the equator, the more signal is lost due to the position from the horizon those satellites are. I regularly get 3-4 ft EPE in Virginia.
Regards,

Moose1am

Offline sonar2000

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Re: GPS Position accuracy
« Reply #17 on: December 23, 2010, 09:23:09 AM »
The first WAAS bird certainly helped us on the southern central east coast. They did however shut it down for a bit as the inland bird was being set up. 
GRS-50 receivers are very good receivers and accuracy is very good.
As was stated using the decimal degrees gives the best accuracy. (about 3 feet + or -).
The fifth digit of the decimal changes with every 2 to 3 feet motion which makes relocation or navigation very accurate.
Using the decimal degrees is very accurate even with a 12 sat receiver as is the case with my handheld. Sometimes this may only be 6 or 8 sats.
Pinpoint accuracy for the user is really experience as the equipment will do the job fine.
Chuck(sonar2000)


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