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en:help:1.4:geolocation [2014/11/05 18:16]
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-<​sub>​[[en:​help|Online Help]] > [[en:​help:​1.4|AlpineQuest 1.4]]</​sub>​ 
-====== GPS position ====== 
  
-The GPS position allows you to display your real location on the map. 
- 
-Most devices now have a GPS chip which is used to compute this location. GPS provides a precise location while not using any cellular network. However, it must have a clear access to the sky, meaning that it cannot be using indoor. 
- 
-{{ :​en:​help:​1.4:​geolocation:​submenu.jpg?​nolink|}} ​ 
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-{{:​icon_help.png?​nolink}} If your device doesn'​t have the GPS chip, or this one is turned off in the Android settings, the network location (much less precise) may be used. 
- 
-To turn on the GPS position and display your real location on the map, you can either: 
-  * Long-press the "''​**GPS Position**''"​ menu button {{:​icon_01.png?​nolink}};​ 
-  * Open the GPS position sub-menu, and click on the "''​**Activate**''"​ toggle button {{:​icon_03.png?​nolink}}. 
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-===== Menu icon ===== 
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-The "''​**GPS Position**''"​ menu button {{:​icon_01.png?​nolink}} icon and color lets you know the current state: 
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-{{:​en:​help:​1.4:​geolocation:​menu-off.jpg?​nolink}} When the icon is white, the "''​**GPS Position**''"​ is turned off. Long-press the button to turn it on. 
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-{{:​en:​help:​1.4:​geolocation:​menu-on-locked.jpg?​nolink}} When the icon is green, the "''​**GPS Position**''"​ is turned on and the current location is displayed at the map center (or being searched). Long-press the button to turn it off. 
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-{{:​en:​help:​1.4:​geolocation:​menu-on-unlocked.jpg?​nolink}} When the icon is green with a lock key, the "''​**GPS Position**''"​ is turned on and the current location is currently not displayed at the map center (you'​re looking somewhere else on the map). Click on the button to center the map on the current location. 
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-===== Localisation information ===== 
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-The GPS will then try to compute your location based on the information retrieved from GPS satellites. 
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-{{:​en:​help:​1.4:​src_geolocation_information_unfixed.png?​nolink |}} 
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-The localisation information box let you know how much satellites have been found yet. In this case, ''​**0/​5sats**''​ means that ''​**5**''​ satellites have been found in the sky, but ''​**0**''​ are being currently used. It means that the current location haven'​t been computed yet. 
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-In some cases, the application can reuse a previously computed location while the new one is being computed. In this case, the old location is displayed in red like in the previous screen-shot. 
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-When the application is sent in the background (like when another one is started), the localisation is temporarily deactivated to save battery. 
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-In addition to your location, the Localisation provides useful information such as your current altitude and speed. 
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- 
-===== Elevations management ===== 
- 
-The elevation of a point is the difference between the altitude of this point and a reference surface of altitude 0 (also called "sea level"​). 
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-However, depending on what is considered to be the surface of reference, elevations can be quite different. This surface depends on the representation of the Earth, which has been shaped in many ways over the last centuries. 
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-Many countries have used their own measure systems, defining representations that best match the surfaces of their own territories,​ and most of them are still used on paper maps. Unfortunately,​ as soon as used outside of their defined areas, these systems become inaccurate and useless. 
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-The GPS, working worldwide, had to choose a system defining a shape that match the entire Earth. A particular oblate spheroid, called [[http://​en.wikipedia.org/​wiki/​World_Geodetic_System|WGS84]] has been chosen as shape, because it provides a good overall approximation while remaining simple. 
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-Based on this choice, GPS's "​WGS84"​ elevations are a good approximation at the Earth scale, but compared to per-country systems elevations, we can have discrepancies up to 50m. 
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-**To reduce these discrepancies and provide more precise elevations, the application convert all GPS elevations towards another system using a more precise shape of the Earth, called [[http://​en.wikipedia.org/​wiki/​Geoid|Geoid]]. However, some slight discrepancies can still be found.** 
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-{{:​icon_help.png?​nolink}} You can find a detailed article of the shape of the Earth on [[http://​en.wikipedia.org/​wiki/​Figure_of_the_Earth|Wikipedia]]. 

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