GPS Systems

GPS is now a part of everyday life, the ability to know exactly where you are on the planet was the dream of every navigator for millennia, now this is available at the press of a button. GPS is widely used in a variety of technologies such as mobile phones apps, cars navigation for both mapping and incident reporting, wildlife tracking which has yielded some interesting results for migratory birds and mammals and preventing crime by tracking desirable objects. This tech has only been available to the public since the year 2000 and has since become the most popular method of accurately establishing a location within metres. 

Introduction

A short history of GPS Systems

The first publicly available Global Navigation Satellite Systems (GNSS) was the USA’s Navstar GPS satellite constellation. This was a satellite-based radio navigation system owned by the United States government established in 1978 for the USA military and made public in the year 2000 by the Clinton administration. America’s newest GPS system is now just one of many that provide geolocation and time information to a GPS receiver anywhere on Earth where there is an unobstructed line of sight to four or more GPS satellites. Other GPS systems include Russia’s GLONASS, the European Union’s Galileo, and China’s Beidou Navigation Satellite System which offer varying degrees of accuracy, the Galileo system being the most accurate at less than 1 metre for public use and up to 20 cm accuracy for paying customers in 2021.

NAVSTAR Global Positioning System satellite
Artist’s concept of a NAVSTAR Global Positioning System satellite, a space-based radio navigation network.

How does a GPS work?

GPS systems use sets of dedicated satellites, called constellations, these are not stationary but are circling the earth so ‘rise and set’ twice a day, the satellites constantly send out signals, the GPS receiver listens for these signals they don’t transmit anything back to satellites. To determine the location of the GPS satellites two types of data are required by the GPS receiver: the almanac and the ephemeris. The almanac contains information about the status of the satellites and approximate orbital information allowing the receiver to see which satellites should be visible. After establishing what satellites should be available for you to get a fix, your GPS receiver requires additional data transmitted by each satellite, called the ephemeris, this data gives very precise information about the orbit and location of each individual satellite. The GPS receiver uses the ephemeris data to calculate the location of a satellite within a couple of metres and then by using the information that was transmitted to the GPS, your position can be calculated by triangulation using the delta in time signal transmitted and when it was received plus the location of the satellites. The ephemeris is updated every 2 hours and is usually valid for 4 hours, so If your GPS receiver has been off for a while, it may take up to several minutes to receive the ephemeris data from each satellite, before it can get a fix, this is known as a cold start. Obstacles such as mountains and buildings block the relatively weak GPS signals, this will ‘lengthen’ and therefore distort the time to receive the data or even give a false location. On a Mobile phone, there is an additional A-GPS mode which uses the cell towers to calculate the initial position of the user very quickly but with less accuracy, unlike pure GPS this may send information back to a server where that might be helpful to process position. Once the receiver calculates its distance from four or more GPS satellites, it can figure out where you are to approximately a 7.8-metre accuracy and depending on the system in use the accuracy might increase. Using GPS for locating a point of the earth is a key component for Geocachers in their quest to find caches, hence the saying follow the arrow.

Photo: ©GSA, ©European GNSS Agency
One of the Galileo Satellite Constellation

Tips and tricks
1 Having obstructions between the GPS and satellites causes issues where 3 – 4 satellites cannot be seen simultaneously, this is most often seen in cities and forests where accuracy quickly degrades.

2 Multi-path or Signal reflection occurs when the GPS signal is reflected off buildings or other objects, this can delay the time-clock signal sent out by satellite and cause a miscalculation again resulting in degradation of accuracy.

3 In the Northern Hemisphere Face the internal Antenna toward open Southern, SW, SE, in the Southern Hemisphere revers this, most of the satellites are clustered around the equator, this will make getting a fix and maintaining on easier.

4 Low batteries invariably cause issues with GPS systems, make sure that your batteries aren’t on their last legs.

5 When you switch on GPS after moving more than 25 miles or replacing batteries keep it in one position in the open air to allow the ephemeris data to update, it will get a fix far quicker than moving with it.

6 Keep firmware up to date, if there are any bugs in your GPS program an update will fix the issues. If there are more up-to-date base maps in GPS standalone system, an update will repair that, too. 

7 GPS systems are not infallible so use common sense and your Mk 1 eyeball to check what you are being told by the system matches reality, learn to read a map and research where you are going. Most Geocachers will have stories of reaching a river or cliff face and being just meters from a cache that could not be reached without retracing their steps and trying another path. 


Favourite Locations

Some areas have it all, great countryside and some of the best geocaches. If you have a favourite location and would like it to be included here, please contact us.

The Moseley’s Recommend Kentisbeare

If you are ever in Devon, you must visit a little village called Kentisbeare! This area is filled with fantastic geocaches placed by a geocacher called heartradio. 

We travelled to Devon for the Mega in 2017, but decided against camping on site because we dragged along a then 6 month old Moseley_Bach with us, so we stayed in a static caravan near Kentisbeare, and accidentally stumbled across these caches nearby. 

In this village and the surrounding area you can find traditional caches, multi caches, a devious mystery cache geo-[he]art, earth caches, letterbox caches and wherigos! And within these caches, there are Church Micros, Village Halls, Little Bridges, Village sign and a Fine Pair!

We spent days exploring the numerous paths and finding the varied containers and some near impossible caches. 

We had to message heartradio a few times for some help, and he always obliged. He passed us one day as we searched for a particular difficult cache and stopped to say hello!

We didn’t manage to complete his caches, and will hopefully return to the area one day to find more! 

Kentisbeare, definitely worth a geocaching visit. 

Kentisbeare Geocaches

Contributed by Lon Moseley, Welshgirl11

Doogee S88 Pro

After years of quite breaking fragile phones whilst Geocaching, when it was time to renew my ageing iPhone I took a look at the market place. One other thing that had bugged me over the years is having to charge a phone daily and if GPS is used heavily having to cart a powerpack to top up the battery, I’m operating system agnostic so wasn’t too bothered the Android iOs ‘wars’. There was one phone brand that leapt out at me which was Doogee’ a Chinese phone brand that is focused on rugged designs. Doogee is part of KVD International Group Limited headquartered in Shenzhen, China, since 2013, which is a long time in the small player mobile-phone world. The phone has a military hardware styling and claims to meet military standards for ruggedness which I don’t doubt. The 10000mAh battery lasts about a week between charges and with heavy GPS use about 3 days and as a bonus can reverse wireless charge other phones to share the power. For positioning, it can utilise GPS, GPS-A, GLONASS & BeiDou and lock times are impressive, with surprising accuracy. It’s tough, heavy and reliable, but it’s not all roses, being a Chinese phone there’s little or no support if anything goes wrong so my tip is to buy off Amazon and use a credit card to have even any hope of warranty.

Update: The SIM card holder broke on the third time inserting. Despite repeated attempts to contact Doodee support, I got no reply. Amazon stepped in and refunded my money, it’s a shame that what was a promising phone was let down by non-existent support and a £2 sim holder .

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Ann@Birdbrook’s favourite caches

GC4WEDK 147 Snooker Challenge D5/T4 Challenge Cache UK
I like a good challenge and this is certainly one. For this cache all you have to do is find 36 caches in a day, simple, well it’s not quite that easy. Basically, you are playing geocaching snooker, different types of cache count as the different coloured balls as in snooker and you have to score a maximum break of 147! See the cache page for the rules. The idea for this cache is “borrowed” from Just-Us-Two, the original cache being GC4NYHP.
Disappointedly we failed this challenge on our first attempt, too many DNF’s and too long spent looking for parking spots resulted in us running out of time. Having learnt from our mistakes we planned our next attempt like a military operation – even having a dry run to check parking spots. We had a great sense of achievement in signing the logbook of the well-hidden nano.

GC1TG4P Intertidal Footprints D5/T3.5 Earthcache UK
I am not a big fan of earthcaches but this one is very special. Coastal erosion at Formby has revealed the sub-fossil footprints of humans, animals and birds preserved in laminated silt exposures. Due to constant erosion and shifting sand, the coordinates are for the general area. We had tried twice unsuccessfully to find this earthcache so signed up for The National Trust Guided walk. Our guide was excellent, answered all our questions and took us to an area about 500m away from the published coordinates where we immediately found human footprints. At the first location, we found Human, Oyster Catcher and what was probably Aurochs footprints. The best discovery of the day was a trail of footprints left by an adult with a child’s set of prints running alongside. They looked so perfect that they could have been made that morning. At the second location a bit further south, we found Crane and Red Deer, here the laminated deposit was a completely different colour. The guided walk is highly recommended for this one, cost about £5.00 – worth every penny!

A Red Deer hoof print from approx 4,000 years ago.

GCKCJV Ghost Village (Wiltshire) D5/T1.5 Virtual UK
This is one of those places I would never have known about, let alone visited if it had not been for geocaching. The virtual cache is found in Imber, Salisbury Plain, a village taken over by the army in 1943 as a training ground. Originally the residents were told that they would be allowed to return after the war but this was never permitted. As the village finds itself in the centre of a military range danger area it is only open to the public at certain times of the year and with very strict access rules. The whole experience is very surreal, the drive across Salisbury Plain with its abandoned tanks to the perfectly preserved church and graveyard.

A house converted into a training room Imber

GC6K8BF Ogof Clogwyn D5/T5 Letterbox UK
I have not found many letterbox caches mainly because there are very few in our local area. While planning a trip to find the oldest cache in Wales this letterbox caught my attention initially because of its type but also it being a D5/T5. I’m not that good with confined spaces but after studying the cache page and a bit of general research on the internet there didn’t appear to be any tight squeezes or anything too difficult. Ogof Clogwyn is rated as a beginners cave therefore it has plenty of space and head room. This cave really has the WOW factor. The walls are lined with amazing rock formed shelves, so, as with any cave/mine, hard hats are a must. I’m surprised there is not an Earthcache here. The hardest bit was getting into the cave as there was a lot of water tumbling out of the entrance which is quite high. Once in, armed with a laminated copy of the excellent instructions it was easy to find the route to the cache. To be honest it would be very hard to get lost. Be prepared to get wet! Oh and the water is very, very cold.
This is one of those caches that you wish you could give more than one favourite point too.
As the cache pages says ‘its simply a pretty cave in a pretty spot”.

Ogof Clogwyn Cave – Photo published by kind permission of cache owner Stuart (Funk to Funky)

GCM7R6 Northside Pub Crawl D2.5/T1.5 Virtual
GCJJVZ Southside Pub Crawl D3.5/T1 Virtual Ireland
If you are in Dublin and love pubs these two caches are a must. All answers to the clues are on the outside of the buildings but the inside of the pubs are worth a look and you really should sample the quality of their Guinness. These two caches are great to do in a group, we had a fantastic weekend of drinking and caching around the City, only realising a little too much Guinness had been consumed when it came to working out the final calculations! Also after visiting the 20th pub the terrain rating maybe a little on the light side……..

A pint of the black stuff always tastes better in a Dublin Pub

GC3D4F9 Arte de Portas Abertas D2.5/T1 Multi Portugal Madeira
I usually avoid Multi Caches especially if they have lots of stages, they always seem a lot of work for very little. This cache guides you through an area that is best described as an outdoor art gallery. A near derelict street of Funchal was brought back to life by The Art of Open Doors project. Local artists were commissioned, each artist being allocated a space/door to express themselves, with their imagination and a few low-cost resources, the street was transformed. As the tourists began to visit they were quickly followed by shops, cafes and bars. The area is now thriving with very little evidence of its past. The final cache is not great but the artwork makes up for this.

Painted doors in Funchal