LBS +Quick Start

Location-based services (LBS) use coordinates from the World Geodetic System +(WGS 84), which is also used as a reference system by the Global Positioning +System (GPS).

The coordinates are based on values for latitude, longitude, and altitude +(elevation above sea level).

The North Pole is 90 degrees North (+90 degrees) and the South Pole is +90 degrees South (-90 degrees). The Equator is defined as 0 degrees; locations +above it have positive latitudes (0 to +90 degrees); those below (0 to -90 +degrees) negative ones.

There are two definitions of North Pole; Magnetic North Pole and True (Geographical) +North Pole. Any application with a compass must check how the API defines +North Pole.

The Magnetic North Pole is the point to which compasses point. The True +North Pole defines latitude as +90 degrees.

Meridians are constant longitudinal (north-south) values. The Prime (Greenwich) +Meridian’s value is 0 degrees. WGS84, which LBS use, defines its zero meridian +some 100 meters east of the Prime one. Locations east of the Prime Meridian +have positive longitudinal values (0 to +180 degrees), those west (0 to -180 +degrees) have negative ones.

As seen in the figure below, latitude lines are smaller near the poles. +At the equator, one degree of longitude is roughly 111.3 km, whereas at 60 +degrees of latitude one degree of longitude is only 55.8 km, which is more +difficult to see.

Getting started +with LBS

This section provides links to the most important documentation.

For +application developers

The Location +Acquisition API is the interface that programmers use to create location-aware +applications. The API gives developers the ability to get location fixes and +to obtain information about the positioning technologies available to the +mobile device.

Technologies

The +main technologies enabled on the Symbian platform by the LBS subsystem are +as follows:

Global Positioning System +(GPS)

The GPS system provides accurate, worldwide positioning. The +main disadvantage of GPS is the long time required to obtain a position fix +when the GPS hardware is first powered. LBS supports Assisted GPS (A-GPS) +to reduce the time required to get a position fix.
Network based positioning

Network +based positioning is typically less accurate than GPS, but often provides +a faster fix of adequate accuracy for some applications.
Secure User Plane Location +(SUPL) v1.0

SUPL defines an architecture for supporting Location Based +Services using IP bearers to connect handsets and network hosts. The Symbian +LBS subsystem contains a SUPL Protocol Module to support SUPL.

+ +

The above figure illustrates how the location information can be +provided to the device. Access to these location methods is provided through +the positioning modules.