GridPoint GB does not collect or transmit any data to anyone (except, if and when you purchase a tip, the necessary communications with Apple’s systems). These tests should not fail, so if you see this message, I’d like to hear about it. What should I do?Īt launch, the app runs a variety of tests on the integrity of its conversion data and routines. Q & A Does GridPoint GB use GPS (and run down my battery) in the background? But if you want to, OS provide an excellent introduction to coordinate systems. Grid north is calculated according to instructions in a 1983 OS publication and verified against a contemporary spreadsheet for coordinate calculations.Īll conversion code is open-sourced on GitHub, and can also be used for batch conversions.Ĭonfused? You don’t need to understand any of these details to make good use of GridPoint GB. The app also calculates your heading relative to grid north, to display alongside the magnetic and true headings. (The app also contains code implementing OSGM02, which converts WGS84 geoid height to height above mean sea level, but this is not currently exposed, since the iPhone does not report raw geoid height). It uses the OSTN02 National Grid Transformation, which OS makes freely available for this purpose, and which is accurate to within 1m. GridPoint GB converts the GPS WGS84 datum location reported by the iPhone into the OS standard OSGB36 datum. For example, the 100m grid reference for the location shown in the screenshot is TQ 304 056. To convert a 5-digit easting or northing to a 4- or 3-digit one, just round off the rightmost 1 or 2 digits. Grid references are more commonly stated to the nearest 100m, with 3-digit eastings and northings. To learn how to read an OS map, see the OS’s map reading resources. Your heading is shown by the orientation of the iPhone symbol. Your location and its accuracy are illustrated, as they would be seen on the grid of an OS map, by a white + and a semi-transparent white circle. Your grid heading, and its accuracy, are also provided. The accuracy of the reference, in metres, is given immediately below these (+/-). Your National Grid reference is given to the nearest metre, with 5-digit easting (E) and northing (N) values, as seen in the screenshot above. Reported accuracy should improve to better than 10m if you are out in the open. While the app is open, your location will continue to be updated. You may need to wait a few moments for your location to be determined. Open GridPoint GB and allow it access to your location. If you like it, you can provide a tip via in-app purchase (see the About tab in the app). It does not operate in other parts of the UK or British Isles - Northern Ireland or the Republic of Ireland - since the coordinate systems are not the same. Please note: this app works only in Britain (i.e. Lets you browse and buy OS Explorer and Landranger maps. Can emit a distress signal, just in case.Calculates next sunset and sunrise times.Has a sharing facility so you can share, copy or store your location.Reports full numerical easting and northing, tetrad, raw latitude/longitude, a nearby postcode, and various heading parameters.Includes an Apple Watch app and associated complication.GridPoint GB uses your iPhone’s GPS and compass to provide your current grid reference and heading, and illustrates how to use this to locate yourself on the map. If you have a paper Ordnance Survey (OS) map, GridPoint GB makes it easy to locate yourself - even when you have no mobile reception.
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