How accurate is your GPS

I was in Wyoming and South Dakota last week for work and spent some time in the bentonite mines. Part of the tour we were shown how they survey the mine sites using their GPS. The GPS that they use is accurate enough that it also gives them height which they use to tell how much material has been taken off the site. To demonstrate the system he put a quarter under a stone in a gravel parking lot and i was the one that got to find it using the GPS (the unit attaches to a metal rod with a point on the end). I followed it until it said I was on the mark (it shows a bullseye) but I was off by a little bit. The read out on the screen said I was close but not quite there, I was off by .5″. That thing was nuts, accuracy within .5″, it also cost 50K.

All that had me wondering how accurate my GPS was and I have no idea. Anyone know how accurate their GPS is?

When I was still a LEO, we had city engineers come to some accident scenes to take measurements. They said when lock onto the satilites, they are within 1/32″. I would guess the ones in a boat or car…..maybe 10′ if your lucky.

I think handhelds with waas capabilities will get you within 8 to 10 feet if i remember correctly.

The answer to this question keeps changing along with advancing technology as well as United States law. The first consumer GPS receivers on the market were far less accurate than the receivers available today even though the satellites are the same. Also, before the year 2000, the military intentionally introduced inaccuracies into the civilian GPS signal for “security” reasons. They called this intentional signal error “Selective Availability”. In May of 2000, President Clinton made a decision to turn off SA and allow civilians access to increasingly accurate GPS signals. The military still has the ability to turn off or introduce errors into GPS signals at any time and with no notice but this ability is generally only used for specific reasons of national security.

The best consumer GPS technology available as of 2009 achieves an accuracy level of 15 to 30 feet under normal conditions. Garmin, currently the most popular manufacturer of GPS receivers, claims their GPS units are accurate to within 50 feet 95% of the time. Even within the Garmin GPS receiver line, accuracy specs differ because of the different chips used in the design of different receivers.

GPS Receiver Design Affects GPS Accuracy

If you are looking for the most accurate consumer GPS unit, it’s important to pay attention to the unit’s chip type. The latest technology in GPS receiver chips is the SiRFStar III from SiRF. With this chip in your receiver and WAAS enabled you can expect to reach the best GPS accuracy levels available under current conditions.
Environmental Factors Affect GPS Accuracy

Many different environmental factors can also affect the accuracy of your GPS receiver. Heavy tree cover, tall buildings, deep canyons, and any location in which your view of the sky is limited can affect how accurate your GPS is. Atmospheric conditions can also degrade the accuracy of your GPS unit.

As you can see, there is no easy answer to the question “how accurate is GPS?”. However, you now know the main factors that can affect GPS accuracy.

Link<<<

Man Onestout, one question and I’m all over the net looking for the answer! Great question!

My HDS 10 will say between 10 and 30 feet (when I’m checking it).

From the Lowrance website…

Expectations
The GPS and WAAS technologies are aids to navigation. Typically, GPS accuracy without WAAS will be around 10-20 meters (30-60ft) or less. With the addition of WAAS, accuracy can be as high as 5 meters (15ft) or less. There are still variables that will effect accuracy such as atmospheric interference.

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can be as high as 5 meters (15ft) or less.

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Intersting Brian. I guess it follows the rule of you get what you pay for.

I have taken my Hbird on the Chippewa flowage come to a complete stop let the boat settle, no wind or current, get a good GPS reading set a way point and drop a marker. Drive a 1/2 mile or better away and then hit the GoTo button, it has consistently been within 2-6 feet from the marker when it announces arrival, I was totally surprised at the accuracy. Not all areas are that accurate this is a good test for a GPS real world. No cheating watch your GPS and not where the marker is then look for where the marker is when the arrival alarm goes off.

The history is pretty interesting too.

My hand held is +/- a few feet, which is find for my applications. My H/bird on my bot has been very impressive. I sunk a milk jug on an anchor rope, then tried to find it solely with my GPS. It was spot on!

Brian,
This information is quite helpful.
How do I find out what chip my
Humminbird 798ci HD SI Combo
uses?
Does the chip reside in the head or the GPS receiver?
I have the internal GPS receiver.
Will adding an external GPS reciever enhance my unit?
Are the GR50 and GRHA compatible with the 798?
Is the GRHA more accurate with this unit?

You can test your own pretty easy. Assuming you’re talking one mounted in your boat:

Tie up to a dock, wait for a good signal, Key in a Waypoint.
Run across the lake and mark another known point (Buoy or Dock). Then go back to the first point and see how far off you are tied up in the same place. (Preferably a dock or point without trees causing interference). Your GPS should tell you how close you are, but depends on number and strength of signals being recieved. Come back a few days, week or month later and check it again.

My handheld Garmin GPSMAP76 varies with signal strength and number of satelites: 6ft is best I’ve done and sometimes my deck post will be 100ft off, due to trees nearby and fewer satelites. I can sit and watch it change, usually from 10ft-50ft and the satelites move in/out of the horizon.

Being I work for a Consulting Engineering Firm, we just tested out some new GPS Survey equipment. The company representative told us the equipment is more accurate than we can hold the unit on a Reciever Pole. Set on a Tripod it is accurate to 3mm (1/8″) Horizontal & 5mm (<1/4″) Vertical.

http://www.sokkia.com/Products/Detail/GRX1.aspx

All the Data Points can be saved in a data collector and downloaded into our office computers, processed and create Topo Maps in less than 30-minutes.

As we continue to look at this potential purchase, I may get to take it for a few days to give it a good test. Thinking of a couple points lakes where I know there are big drop-offs and ledges to drill a bunch of holes this winter, check and mark depth at each hole, then use the GPS to points survey them and collect data. Go back in office or on laptop and create some lake contour maps.

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How do I find out what chip my
Humminbird 798ci HD SI Combo
uses?
Does the chip reside in the head or the GPS receiver?
I have the internal GPS receiver.
Will adding an external GPS reciever enhance my unit?
Are the GR50 and GRHA compatible with the 798?
Is the GRHA more accurate with this unit?

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I know zero about Lowrance units and less about Hbirds.

Generally speaking the external antenna’s will give a faster (more accurate) reading than the internal antennas.

I have an internal on my HDS 10 and use it for navigation at night following a route which follows the river channel and “other” places. So far it’s kept me in the channel and away from the navigational markers…although those darn trees get in the way once in a while.

Disclaimer: I run my route going out to ensure the “cans” haven’t changed locations or other obstructions aren’t in the way…Always use two forms of navigation.

Brian,

When did you upgrade from the 8″? Have you thought about
adding a LGC-4000?

DD

Survey grade and consumer grade GPS are two different animals. The surveyors I use have equipment that is accurate enough to tell the difference of the thickness of a dime. They also pay $30-$40K for their equipment.

You really do get what you pay for.

I remember when GPS for fishing was relatively new. I had a handheld unit and was fishing from a friend’s boat in ‘Bago. We marked a reef we wanted to try after dark,dropped a bouy,then came back that night.

We were out there,right on the place the GPS said our bouy was,looking around with a spotlight and unable to locate the marker.. I remember my friend doubting that “this GPS crap” really worked as advertised.

Then we heard the now-familiar tap-tap-tap of the small plastic marker bouy against the boat’s hull.

That’s close enough for me.

So you’re telling me that my H20c won’t help me find a penny in a hayfield?

I’m fine just getting in the general area, especially for ice fishing. Getting close means I get to fire up the auger, make a little noise, and smell a little exhaust, all of which make me a happy man.

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I’m fine just getting in the general area, Getting close

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Kinda like your birthday huh?

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I’m fine just getting in the general area, Getting close

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Kinda like your birthday huh?

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Just like carbon dating.

I have a $300 Garmin Nuvi in my truck and if I am anywhwere in the UP or especially up near Ashland WI the damn thing will take me right into the damn woods and waters… (where no roads exist)
I guess its the terrain?

Have you ever seen the ones in todays tractors/combines? I have friends here in IA that use them now for strip tilling/planting. They are so accurate they can apply the fertilizer right into the 1″ strip that they till in the fall. I can tell you my hand held XGOG “sometimes” gets me to 6′ but sometimes I am lucky to get 20′ all depends on the situation. Of course mine cost $200 and the ones in the tractors cost $4000 but they are amazing. I rode with him last year, hand OFF the steering wheel.

Found this for the Humminbird GPS receivers

http://forums.sideimagingsoft.com/index.php?topic=229.0#top