Localisation

The Localisation feature 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, and doesn't need to use any network. However it must have access to the sky. Alternatively, you can use another location provider if your device doesn't have a GPS chip.

You have first to activate the geolocation. You can either:

• Long-press the Geolocation menu button ;
• Open the Geolocation sub-menu, and click on the Activate button .

The GPS will then try to compute your location based on the information retrieved from GPS satellites.

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.

In some cases, AlpineQuest 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.

When the application is sent in the background (like when another one is started), the localisation is temporarily deactivated to save battery.

In addition to your location, the Localisation provides useful information such as your current altitude and speed.

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”).

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.

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.

The GPS, working worldwide, had to choose a system defining a shape that match the entire Earth. A particular oblate spheroid, called WGS84 has been chosen as shape, because it provides a good overall approximation while remaining simple.

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.

To reduce these discrepancies and provide more precise elevations, AlpineQuest convert all GPS elevations towards another system using a more precise shape of the Earth, called Geoid. However, some slight discrepancies can still be found.

You can find a detailed article of the shape of the Earth on Wikipedia.