How Low Can You Go....

[ishoot308]

Originally Posted by Slickcraft

The +/- degradation for non military GPS receivers, known as "Selective Availability", was eliminated in 2000.
http://www.gps.gov/systems/gps/modernization/sa/

Correct and I believe if you enable the "WAAS" (wide area augmentation system) feature on your GPS this gives you an accuracy of 3 meters or less...

Dan

[Rich]

GPS system specs and actual reality seen by end users can be two different things.

I'd suggest that you check with your GPS receiver vendor to see what they say.

As an example, many people have a Garmin GPS receiver, here is how they answer the 'how accurate is my GPS' question:

GPS accuracy
Today's GPS receivers are extremely accurate, thanks to their parallel multi-channel design. Certain atmospheric factors and other sources of error can affect the accuracy of GPS receivers. Garmin® GPS receivers are accurate to within 15 meters (49 feet) 95% of the time. Generally, users will see accuracy within 5 to 10 meters (16 to 33 feet) under normal conditions.

Raymarine says something similar:

Understanding GPS Accuracy Statements

What do the quoted position accuracies in my GPS manual actually mean?

GPS position accuracy is normally quoted as a statistical probably of how accurate the position from the GPS will be.

In standard GPS mode (not using differential corrections), the Raymarine Raystar 120 and 125 sensors will give a position that is within 15m (33ft) of the true position 95% of the time.

In satellite differential mode, the Raystar 120 and 125 sensors will give a position that is within 5m (16.5ft) of the true position 95% of the time.

Depending upon the type of fix, 95% of all the position calculations (one occurring every second) will be within an imaginary circle of radius 15m or 5m from the true position. The GPS is still operating within its specification if occasionally position fixes fall outside of this imaginary circle.

As GPS accuracy is dependent upon the positions of the visible satellites, the above specifications are assuming that the HDOP reading from the GPS is 2.0 or lower.

What brand GPS do you have and how old is it? My guess is that they will state something similar, unless you are using a survey quality GPS receiver, which most boaters do not have on their boat.

[Slickcraft]

Originally Posted by ishoot308

Correct and I believe if you enable the "WAAS" (wide area augmentation system) feature on your GPS this gives you an accuracy of 3 meters or less...

Dan

http://www8.garmin.com/aboutGPS/waas.html

Yes you should enable WAAS on your GPS. A fixed ground site in the general geographic area with known coordinates receives the GPS signal and calculates instantaneous errors. Correction data is then broadcast which your GPS unit uses to improve accuracy. This will add a small amount of time for your GPS to sync.

Not all GPS units have WAAS enabled by default.

[thinkxingu]

Originally Posted by Slickcraft

http://www8.garmin.com/aboutGPS/waas.html

Yes you should enable WAAS on your GPS. A fixed ground site in the general geographic area with known coordinates receives the GPS signal and calculates instantaneous errors. Correction data is then broadcast which your GPS unit uses to improve accuracy. This will add a small amount of time for your GPS to sync.

Not all GPS units have WAAS enabled by default.

Just noticed that my Garmin has a couple options in settings: GLONASS and WAAS--am I right in thinking WAAS should be turned on and GLONASS off?

Sent from my XT1528 using Tapatalk

[Slickcraft]

Originally Posted by thinkxingu

Just noticed that my Garmin has a couple options in settings: GLONASS and WAAS--am I right in thinking WAAS should be turned on and GLONASS off?

Sent from my XT1528 using Tapatalk

WAAS improves the accuracy of the US GPS system but may result in longer sync time if you have poor sky visability, like in the woods with a hand held GPS. On open lake you should have WAAS on.

GLONASS is the Russian equivalent of the US GPS system. Your Garmin can use those satellites to assist in seeing enough satellites to sync quickly and "maybe" at times improve accuracy. It is used in many handheld units and smartphones for a quick location fix. For use on the lake, it could be left on or not. I'll try it both ways near some markers.

[thinkxingu]

Originally Posted by Slickcraft

WAAS improves the accuracy of the US GPS system but may result in longer sync time if you have poor sky visability, like in the woods with a hand held GPS. On open lake you should have WAAS on.

GLONASS is the Russian equivalent of the US GPS system. Your Garmin can use those satellites to assist in seeing enough satellites to sync quickly and "maybe" at times improve accuracy. It is used in many handheld units and smartphones for a quick location fix. For use on the lake, it could be left on or not. I'll try it both ways near some markers.

Thanks for the info, Slickcraft. I threw WAAS on and, for the first time, the last red buoy coming past Bryant's Point (towards Greene's Basin)--which was recently moved in, no doubt because of the low levels--actually showed to my left. Certainly much more accurate than when off.

Does anyone know if there's a way to change the location of buoys in GPS systems or if it's only via the maps software?

Sent from my XT1528 using Tapatalk

[DBreskin]

Originally Posted by thinkxingu

Does anyone know if there's a way to change the location of buoys in GPS systems or if it's only via the maps software?

Strictly speaking there are no buoys or any other features in the GPS system. The GPS systems only provides your location on the globe. Whatever mapping software or system you use provides the landmarks and other mapped features. Many systems allow you to add waypoints, use custom maps, or do other things. For example, Navionics will allow you to connect your depth finder to your GPS for making real-time maps of the lake bottom. You can also share this data with others for crowd-sourced up-to-date bottom contours.