FAQ: GPS Accuracy at Check In and Out

Modified on Mon, 1 Apr at 5:20 PM

Why is my recorded location sometimes inaccurate?

We sometimes hear from clients that occasionally (not always) the location that is recorded at the time of checking in or out of a service is inaccurate and that this inaccuracy can be up to or even more than 1000 meters. Unfortunately GPS technology (or more generically called "Location Services") is still a bit hit and miss and so we have written this Help article so you can better understand this issue.

Each phone has a facility called "Location Services". Location services is a suite of software (hosted on Android or Apple iOS) that is designed to derive the most accurate set of geographic coordinates as possible. Pet Sitter Plus has no control at all over location services; it is controlled jointly by the manufacturers of the phones themselves and by the manufacturers of the operating systems of the phones.

Our role (the role of PSP) in the process of GPS check-in/check-out is fairly simple - we ask the phone a simple question - "Where are you?". In programming terms we say "Give me the set of coordinates that represent where you are right now." By "now" we mean "this second". We do not say to the phone - "If you are not sure where you are right now, then give me your last known location". Instead we use software to force the phone to re-check its whereabouts "right now" and if the phone cannot provide us with a refreshed set of geographic coordinates (based on "now - this second") then we record only the time of the check-in without the location. If this happens, then against the check-in time on the service record you will see the notification "(No Location)".

So - when your sitter clicks "check-in" Pet Sitter Plus asks the phone "Where are you right now?" and the phone either responds with "I do not know where I am", leading to "(No Location)" being recorded or "location services" on the phone derives the best set of coordinates it can – based on all the technologies it has at its disposal (such as GPS, Mast triangulation and WIFI group sourcing of location information) – and gives that set of coordinates to Pet Sitter Plus.

Is GPS Accurate?

The short answer is "sometimes". It is important to say at this stage the GPS technology (in general) has it flaws. It is not 100% accurate all the time. This has nothing to do with Pet Sitter Plus and everything to do with the state of the art of the technology used by phones (Location Services).

GPS (or Global Positioning System)

If your sitter is outside of your client's house when they try to check-in, then the most likely scenario is that a number of satellites are connected to your sitter's phone via its GPS chip and, as a result, your sitters' phone has a very good understanding of where it is. This is usually within 5 to 10 meters.

GPS is the best and most accurate way to derive location information but more often than not it will not work inside buildings and so for best results sitters should check-in before then enter the client house.

However, when your sitter leaves a client's house, it can take some time for the satellites to re-establish connection to the phone, so it is not true to say that stepping outside the house to check-out will always give a fully accurate result. If the phone is still trying to negotiate with the satellites then it will probably fall back on mast triangulation which is discussed below.

Mast Triangulation

If your sitter is inside a clients house, then GPS (the most accurate system for deriving locations) doesn't generally work because the phone no longer has line of sight of the satellites. The phone then switches to a system called "mast triangulation" which works by deriving location coordinates by triangulating on one or more cell towers. This is very much less accurate than GPS because if you are in a low cell coverage area and your phone is connected to one tower only, it cannot effectively triangulate and therefore the location can be inaccurate by up to 3/4 of a mile.

The bottom line is that if your sitter is in a poor reception zone where the phone is connected to only one mast, then if they then attempt to check-in or check-out while inside a house or an apartment block, the resulting "check-in" and "check-out" location recorded could be inaccurate by up to 3/4 of a mile because of the inaccuracy inherent in the mast triangulation system.

For best results, the guidelines are to always check-in before entering a building and check-out after leaving a building so that your phone is in line of sight of the satellites. Typically when we look at the Staff Activity report of any client, I would expect to see some (but only a few - usually around 10%) of the check-in/check -out locations showing an inaccuracy of between 100 to 1000 meters because of this issue.

If you are interested and you would like to know more about how location services derives its location on the phone then please read Why is the Check-in and/or Check-out function Not Working on my iPhone? or Why is the Check-in and/or Check-out Function Not Working on my Android Phone? to help understand how your mobile phone determines and provides your location to Pet Sitter Plus.

An additional problem occurs when the phone is not setup for maximum accuracy. Android devices in particular have an "accuracy" setting which must be set to "accurate". If this setting is not set, then recorded locations could be very inaccurate.

Finally, will an APP help?

In two particular circumstances the APP (when it arrives) will provide some help, but it is not going to be the panacea that some people may assume. So for example, if you are inside a building, such that your phone cannot see the satellites (so no GPS) AND you are in a poor cell zone, so location accuracy is poor, the fact that your application is an APP (instead of a mobile website) will not help at all, and this scenario unfortunately constitutes the majority of the problem.

However, say you have no cell coverage at all, but your phone is connected to the satellites via GPS (which typically means you are in a field in the middle of no-where), then in that particular situation your phone (APP) will still be able to record (and store) location information even in the absence of an internet connection. That is because an APP has the capacity to continue to function but most importantly to "store" location information locally when there is no cell coverage whereas a mobile website does not have either of these options. This is (for example) why Google maps (which is an APP) keeps working even when you are in the middle of nowhere with no cell coverage. In this scenario it is using GPS (satellites - which does not require internet) to derive location. It is not using mast triangulation (which requires internet) to derive its location. If however you were driving though a tower block, with no cell coverage, then your phone could not see the satellites AND would have no access to the internet, so even Google maps would stop working in that scenario too!

The most common situation is one where your phone is inside a building (no access to GPS) AND the cell coverage is poor or non-existent. It is this situation an APP will perform no better than a mobile website. The real answer is that "Location Services" has to improve and there is lots of optimism and reasons to believe that it will.

APPs will on the other hand be great for the purpose of full walk tracking, because when you are on a walk, you are generally "outside" and so your phone is always connected to GPS. In this situation we will be able to "sample" accurate location data many times a minute, store it in the APP, and then transmit it to the PSP server immediately (when there is signal to do so) or if there isn't any signal, transmit it later when there is a signal. This way we will be able to reliably create mapped walks once the APP technology is in place.