Cords off

[bkollette]

Having cached for a while , it seems that our co-ordinances of late consistently are off by 35-65 ft. Any idea why? Thanks for any help

[Keystone]

There are many possible explanations, but first it would help to know what handheld GPS receiver or Smartphone + App that you're using.

[+NYPaddleCacher]

There are many possible explanations, but first it would help to know what handheld GPS receiver or Smartphone + App that you're using.

 

This question should not suggest that different smartphone apps are going to be significantly different in terms of accuracy. All geocaching apps, and any other apps that use location services, get their data from a location service in the smart phone which uses data from the GPS (and cell/wifi triangulation). If you put three different Geocaching apps on the same phone, they *should* all have to same accuracy. I suppose that if the GPS chip was using WAAS or GLONASS, and an app wasn't using it that could make a difference, but even with out it, 35-65' seems pretty far off.

 

First thing I would check is the datum used (it should be WGS84) and coordinate format (it should use Degrees Decimal Minutes).

 

 

[+WearyTraveler]

Another data point to consider would be tree cover. It can foul up accuracy. Or - placed with leaves in the trees - searched after fall. May not be the answer, but something to consider.

[+Cache O'Plenty]

Depending on your unit, perhaps it needs to be calibrated.

[+hzoi]

Depending on your unit, perhaps it needs to be calibrated.

I could be wrong, and I am by no means an expert, but I don't believe there is a way to calibrate a GPS receiver in order to increase the accuracy of its location computation. It is either receiving location data from GPS sats or it isn't. I can calibrate the electronic compass on my Montana, but that doesn't affect GPSr accuracy, just how well the unit can determine which way I'm pointing it.

 

I can set it to use GLONASS or WAAS/EGNOS, however, and that does help accuracy by telling the unit to use more sats in its position calculations. If that's what you mean, then yup, concur.

[+rjb43nh]

If you try to use a handheld GPS receiver such as a Garmin 64S in the middle of a city with tall buildings like Chicago, you can find readings that are up to 1000 feet off. The reason is signal reflections off some buildings and signal blockage by other buildings. To get best accuracy you need a clear view of the sky and an adequate number of GPS or GLONASS satellites in view. In the wild, trees, cliffs, etc., can also cause errors.

 

As to smartphone GPS accuracy, GPS.gov says: “GPS-enabled smartphones are typically accurate to within a 4.9 m (16 ft.) radius under open sky”.

 

GPS.gov also says: “... the government commits to broadcasting the GPS signal in space with a global average user range error (URE) of ≤7.8 m (25.6 ft.), with 95% probability. Actual performance exceeds the specification. On May 11, 2016, the global average URE was ≤0.715 m (2.3 ft.), 95% of the time. To be clear, URE is not user accuracy. User accuracy depends on a combination of satellite geometry, URE, and local factors such as signal blockage, atmospheric conditions, and receiver design features/quality.“

[+SerenitySearchers]

We have found this more recently than in the past. Our accuracy at times has been off by say 40 feet consistently... this is when we figure it is an atmospheric condition and we adjust our search area, or we take a break for an hour or so.

 

Of course there are many things that can affect it, but this is our biggest thing we run into.

 

Sometimes this can be frustrating, but we just try to keep the attitude that it adds to our adventure

[+barefootjeff]

If you're using a phone, make sure it's set to use GPS only for location. If the phone decides for whatever reason to switch to cell tower triangulation, it can be quite some distance off.