The Global Positioning System (GPS) traces our position giving the terrestrial coordinates (Zone, Latitude, Longitude, Height, Time and other data).
The datum is obtained utilizing the information given by 24 satellites rotating around the Earth.
In order to obtain the datum of coordinate it is necessary a connection of the device with at least 4 satellites: the higher is the number of satellites visible through the instrument the more precise is the readable datum.
When you are in some zones with any kind of natural and artificial obstructed line of sight to the satellites, blocking the electromagnetic waves (i.e. in woods or inside a building) the GPS system cannot function, because it is not possible to establish the connection with the satellites: in these situations it is not possible to detect the coordinates using this technology.
The operating principle is based on the method of spherical positioning, consisting in recording the time taken by the signal to run the distance satellite-receiver. If you know the precise position of at least 3 satellites in order to have position on a two-dimensional map and 4 in order to have a 3D (three- dimensional) position and the time taken by the signal to reach the receiver, it is possible to establish the position in the space of the receiver itself. When you use a GPS detector it is necessary to place the device in an unobstructed line of sight to the satellites or, however, in a place where it is possible to receive the signals from the satellites rotating above us.
In order to use the GPS properly it is necessary to be in the open air, being careful to have the overcast sky above you trying to stay far from walls, and if it all possible in a free place without any plants. It is necessary to keep the device in horizontal position, with the antenna (in some cases embedded in the device) free from any blockages and not covered by hands.
When the device is on, it will indicate that it shall connect with the satellites, and therefore it is necessary to wait for some minutes: usually, an icon on the display shows the progress of the operation.
When this operation is ended, the device shows that it is ready to be used; in some cases the accuracy of the measurement is shown as well (i.e. in metres).
It is possible to utilize the GPS receivers, which a lot of smartphones and tablet are fitted with, in order to establish the coordinates of a point.
The following two free applications can be used to determine the geographical coordinates with the aforesaid devices.
It is necessary to take into account that the street satellite navigators are made in order to guide the user on the streets. Therefore, the measurement corrects the position of the cursor to the nearest street: this correction is called “back on track” and it offsets the inevitable errors of mapping and position.
As regards the Tom Tom, for example, the user enters the menu tapping on an empty zone of the display, goes to the second page, taps on “ Browse map”, taps on “Find” and then on “GPS position” which will give the current position. Alternatively to the first page of the menu the user can tap on “Preferences” and, on the third page on “Show GPS Status” which allows the user to read the position and choose the favourite visualization format.
It is also possible to use a third method consisting in entering “browse map”, tapping on “Options” and select the item “Coordinates”, henceforth the coordinates of the cursor will be shown on the display.
This kind of devices offers a high level of sensitivity and enables the user to obtain coordinates with a precision level of 0,5 metres.
They can operate properly under wood coverage or in urban environments.
The description of the functioning of these devices is beyond the purposes of this guidebook.
All the information given in this guidebook is purely indicative and under no circumstances CEI can be considered responsible for the accuracy, entirety, correctness and reliability of the information here reported.
All the operations of coordinates’ detection fall upon the responsibility of the final user who can use the device/s he considers to be the most adequate.