Wednesday, April 24, 2019

Why are my coordinates so far off?

I originally posted this blog back in 

May of 2016.  I recently received some questions

about how to get accurate coordinates.

So I updated the information in this post and...

here is the updated info!!!

Here are some fun facts about

the GPS Satellite Constellation

(the GPS system we use).

The Air Force manages the constellation to ensure the availability of at least 24 GPS satellites, 95% of the time. For the past several years, the Air Force has been flying 31 operational GPS satellites, plus 3-5 decommissioned satellites ("residuals") that can be reactivated if needed.

As of January 9, 2019, there were a total of 31 operational satellites
in the GPS constellation, not including the decommissioned, in-orbit spares.

  • The United States government currently claims 4 meter accuracy for civilian GPS. Mind you, that's the minimum. Some devices/locations reliably can get 3 meter accuracy.  4 meters is about 12 feet - so the best you can get is about a 24 foot diameter circle.
  • The first GPS satellite was launched in 1978.
  • A full constellation of 24 satellites was achieved in 1994.
  • Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit.
  • A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended.
  • Transmitter power is only 50 Watts or less.

Most geocachers have run into either a geocache

whose coordinates are less than desirable.

The worst coordinates for a geocache I ever attempted to find

were more than 2 miles off!!!

Oh, and btw... even with the coords
more than 2 miles off, we got a FTF on that cache!

(via a hint from the CO).

All sorts of things can throw off coordinates including clouds, weather, trees, buildings, and sometimes just the minerals in or on the ground at the ground zero.  We have a LARGE geocache hidden in a giant stack of granite blocks.  We get plenty of DNF logs!  Good luck getting a decent lock there - plenty of bounce.

Another factor in accuracy is time.  Here is an example of GPS accuracy from a handheld GPS (Garmin Oregon). The first image was taken 1 minute after the GPS was switched on , the middle image is after 2 minute and the last image is after 3 minutes. You can see on the GPS screen that more satellites are being received as time goes on (the green bars) and the Location coordinates are slowly changing as the accuracy begins to come down to the final 9 feet. The final Location coordinates are N51°35.203' W4°19.501' which can be considered quite accurate.

So, knowing all this - how do we get more accurate coordinates for a cache.

When placing a cache you need to record the coordinates from the GPS or phone and make sure they are as accurate as possible. This ensures people looking for your cache will have the best possible chance of being close to it. If you don't record the coordinates properly and people look for your cache on a day when accuracy isn't that good they could be many yards or meters (or sometimes miles) from the cache. The following steps will help you get the best coordinates you can.

  1. At the cache location, hold your GPS or phone so it has a clear view of the sky – or as clear of any obstructions such as trees or buildings as you can. You can place it down on the ground or on a convenient post or just hold it in your hand. It's recommended you need to leave it like this for at least 10 minutes. If you've just switched it on or it's been in your rucksack or a pocket you may need to leave it a bit longer. This ensures it has a chance to pick up the signal from as many satellites as possible.
  2. Check the accuracy figure shown on the screen (see the images for examples). It will slowly decrease as the GPS picks up more satellites but will eventually stop and that indicates the best accuracy you will get at this time. Wait until the accuracy figure has stopped and drops no more
  3. Record these coordinates either by writing them down or marking them as a waypoint.  Note: The Geocaching® apps show your current location while navigating to any geocache using the compass feature.  I would also recommend, if using this method, to revisit the same site several times (hours apart) to get multiple readings (see manual waypoint averaging below). 

Waypoint Averaging
Another way of making sure the coordinates are good is to take several different readings at the cache and then average them. To be really accurate you should do this over several days because on any particular day your GPS may not be able to pick up as many satellites as on other days which will affect accuracy. You can average waypoints manually or use the averaging feature of your GPS if it has one (not all of them do but the manual method works with any GPS or phone).

Manual Waypoint Averaging (handheld GPS or phone)
Record the coordinates at the cache location using step 1 to 3 above. Then walk about 30 or 40 feet (10 to 13 meters) away from the cache, turn and then walk back to the cache waiting about a minute at the site before recording the coordinates. Do this a second, third, fourth and even fifth time from different directions. You will find you have a slightly different coordinates each time. You can now 'average' these coordinates to get the best possible ones. This is how it's done.  I recommend waiting hours not minutes between readings as you will be syncing with different satellites.
Let's say your five separate readings are these:
N51° 42.634' W4°19.915'
N51° 42.636' W4°19.917'
N51° 42.637' W4°19.917'
N51° 42.633' W4°19.915'
N51° 42.634' W4°19.919'
Take the last part of the N to give you five numbers like this, 634, 636, 637, 633 and 634. Add them together to give a total of 3174. Divide this by the number of readings (5) to give you 634.8 or rounded up, 635.
Now do the same with the last part of the W which gives you 915, 917, 917, 915, 919. Added together this is 4583. Divide by 5 again to give you 916.6 or rounded up to 917. Your best coordinates are therefore N51° 42.635' W4°19.917'

GPS Averaging Feature (handheld GPS only)
If your GPS has the feature to average waypoints then use that. It will be an option in the menu. From the averaging screen you create a new waypoint and press Start. The GPS will then start recording the coordinates for a period of time. When it's finished you can either use that value or continue the averaging by repeating the process. Please refer to your GPS manual for more details.

Two last Tips:
1.  Keep your GPS calibrated.  This will definitely help with coordinates.
2.  Remember the +/-     If I hide a cache and have +/- 10 feet on my coordinates (a 20' circle) but my GPS is off to the east - then you come along and let's assume you have +/- 10 feet but you are off to the west -  this means we just enlarged that 20' circle to a 40' circle.

Have patience - sometimes it is best to stop looking at your GPS and use what we call "geo-sense".  Look around and ask yourself - Where would you hide it?  Believe it or not - it works quite well.

I compiled this information from numerous sites including  Remember, even states your coordinates SHOULD be as accurate as possible.

 That is all for now
Till next time...

Don't forget to visit our favorite Geocaching Store

Stay Safe & Keep Caching!!!

Suffolk Nana & Papa
 - - - or just plain ol' - - -






On Twitter at: @SNAPgeocaching

On Instagram at: snap_geocaching

Thursday, April 18, 2019

Adding some Counties in North Carolina

It has been almost 2 years since Nana & I found the Virginia Counties Challenge Cache.

That particular Challenge Cache required a cacher to find at least one cache
in every county of Virginia - I think it is time to try another state!!!

The question was - Maryland or North Carolina???

Either one would require some travelling.
As far as Maryland goes, we already have 8 of 24 counties found.
As far as North Carolina goes, 56 of 100 counties found.

We travel through North Carolina all the time!

We decided, at least for now, to make a short trip to try to
knock out at least a few counties in North Carolina!!! 

BEFORE our quick trip!

It was never intended to be a long trip!
But I wanted to 1) test out my sore knee and
2) see if I could get out of my geocaching slump!!!

Day 1

The trip south was great but we were amazed at how
high the water was in the rivers and lakes!!!

GC5N6Z6 - 83 NC CWGT Engagement of Windsor
although a little muddy from the high water, Nana & I made the find quickly

GC2MRGR - Aurora's Christmas Welcome
this one had us going for a minute or two but Nana spotted it!

The list I made up had 4 geocaches on it for Pamlico County.
Not sure what our problem was but we logged a DNF on 3 different caches
and then posted a note for the fourth!!!  I thought we were going to come
up blank in this county but remembered some guardrail caches in the County.
Luckily for us we were able to locate one of them to color in the county!!!

GC2PEGH - Kershaw Road E.G.G. Series # 1

GC1ADKD - Waiting for the Ferry
A very fast find here!

GCGEM0 - Ol' Grandpappy
A very nice Virtual cache!!!
Awarded it a favorite point and named it the winner
of the "COVETED" SNAP!!! Cache of the Day Award!

GC1MNB0 - Old Glory#2-Wild Hogs
another fast find and another favorite point awarded!

Day 2

GCEFA7 - Webfargo # 2 - I saw the light
Another nice Virtual cache which also
earned a favorite point and was named the
winner of the "COVETED" SNAP!!! Cache
of the Day Award!

GC5NN7R - 87 NC CWGT Fort Anderson
A very fast find!

GCGFRV - Old Brunswick Town
another great Virtual cache

GC5NYF5 - 88 NC CWGT Fort Johnston
another quick find!

GCGFRX - Red #2
another Virtual cache that gets a favorite point!

GC67E - virtual cache of oib
really loved all these Virtual caches!

we made a quick dip into South Carolina to pick up a county there!

GC3BGEQ - Daughter of a Founding Father
An old church with lots of history earns a favorite point!

GC3XQJH - The McCoy Sisters
a quick grab here!

GC1NK29 - The Ghost of Clare Townsend
a quick puzzle cache after stopping for the night!

Day 3

GCAE35 - Meadow and more!
Loving these country Virtual caches!

GC7B68N - Around and Around it Goes Again
A very interesting location earns a favorite point and ends up being
awarded the "COVTED" SNAP!!! Cache of the Day Award!

GCF1B1 - Past Guardians of the Night
another great Virtual cache

GC67Q3B - VFW Memorial
a very quick find - could have taken a long time!

GC5AH55 - Be square
another quick find for us!

GC53AT0 - 366 Day Calendar Challenge
We always try to grab Challenge caches we qualify for - a fast find!

GC7AG89 - The Rear Admiral from Tarboro
our last find of the day and trip!!!

AFTER our quick trip!

 That is all for now
Till next time...

Don't forget to visit our favorite Geocaching Store

Stay Safe & Keep Caching!!!

Suffolk Nana & Papa
 - - - or just plain ol' - - -






On Twitter at: @SNAPgeocaching
On Instagram at: snap_geocaching