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GpsSensor
Global Positioning System (GPS)
Put simply GPS is a system that uses satellites to determine your current position, which in civilian use is most commonly found in car navigation systems. Portable GPS receivers are available and can be found in a range of portable devices, even in some mobile phones. Mediascapes can use GPS to track the user's position and to trigger events when they enter defined locations.
Characteristics
Interaction model
- The user should establish whether they have a GPS fix. The Mscape Player displays an icon to show the current GPS status. For more information see Having trouble with GPS?
- Once a fix is confirmed no further interaction is required. The system will track the user as they walk around; though it should be noted that in some situations the GPS fix can be lost.
Coverage
GPS offers worldwide coverage; however, since it relies on signals from satellites, it will not work inside buildings and can be unreliable in heavily built up areas, particularly where there are many tall structures. As a rule of thumb, the more sky you can see the better and more reliable the signal and the more accurate the resulting location data. In cases where the number of satellite signals are reduced, or are bouncing off buildings, the location data may be subject to 'drift': it may become inaccurate or shift, even when the user is stationary.
Note also that the satellites are in constant motion, so reliability can change depending on the time of day, week or year. As such it is a good idea to test a mediascape at different times, particularly if some sections are in areas with poor coverage (e.g. built-up areas).
Latency
Once a fix is established position information is updated frequently (usually once per second), so long as the fix is maintained. If the fix is lost, for example when someone enters a building, there will be a slight delay after they exit the building before the fix is re-established.
Initially establishing a fix - for instance after a unit has been switched off for a prolonged period - can take some time whilst the unit gathers data from satellites. Once this data has been gathered a fix can be re-established relatively quickly; for example when the device is switched off and then back on later the same day.
When time is a factor, for instance when a mediascape is being used by the public, it is recommended that devices are placed in a location where they can gather satellite data well in advance and switched on with the GPS unit active (the simplest way of achieving this is launching the mscape player software).
Hardware
See the list of
Recommended hardware for devices that include GPS or for add-on GPS units and also
Setting up GPS on Mscape Player.
Using GPS in mscape maker
The GPS sensor
The GPS sensor object has events that can be used to determine whether the unit has a GPS fix. This can be used to ensure that GPS dependent functionality is not started until a fix is established, or to signal a warning when the GPS signal is lost.
The GPS sensor can also provide location information as well as the angle and speed of travel. It is important to understand that these are only updated when the user is in motion. The angle is not necessarily the angle they are facing, but is the angle between the last recorded point and the current point.
GPS and maps
GPS comes into its own when combined with a map. Once you have
Acquired a map with associated coordinates you can add regions that use the GPS sensor to trigger events.
Add a map to your mediascape by right-clicking the GPS sensor and selecting 'Import Map File(s)':
The PlaceEditor will now display your map, and along the bottom you will see controls to move and zoom the map in the editor and to add regions:
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