The Position class is a utility providing bundle developers with a consistent way of handling geographic positions in OSGi applications. The Position class is intended to be used with the Wire Admin service but has wider applicability.

The Position class is designed to be compatible with the Global Positioning System (GPS). This specification will not define or explain the complexities of positioning information. It is assumed that the reader has the appropriate background to understand this information.

703.1.2 Entities

• Position - An object containing the different aspects of a position.

• Measurement - Contains a typed measurement made at a certain time and with a specified error.

Figure 703.1 Class Diagram, org.osgi.util.position

The Position class is used to give information about the position and movement of a vehicle with a specified amount of uncertainty. The position is based on WGS-84.

The Position class offers the following information:

Longitude and latitude are represented in radians, not degrees. This is consistent with the use of the Measurement object. Radians can be converted to degrees with the following formula, when lonlat is the longitude or latitude:

degrees = (lonlat / π) * 180

Calculation errors are significantly reduced when all calculations are done with a single unit system. This approach increases the complexity of presentation, but presentations are usually localized and require conversion anyway. Also, the radians are the units in the SI system and the java.lang.Math class uses only radians for angles.

A Position object must be immutable. It must remain its original values after it is created.

The Position class is not final. This approach implies that developers are allowed to sub-class it and provide optimized implementations. For example, it is possible that the Measurement objects are only constructed when actually requested.

Positioning information is never exact. Even large errors can exist in certain conditions. For this reason, the Position class returns all its measurements as Measurement objects. The Measurement class maintains an error value for each measurement.

In certain cases it is not possible to supply a value; in those cases, the method should return a NaN as specified in the Measurement class.

The primary reason the Position is specified, is to use it with the Wire Admin Service Specification. A bundle that needs position information should register a Consumer service and the configuration should connect this service to an appropriate Producer service.

The security aspects of the Position class are delegated to the security aspects of the Wire Admin service. The Position object only carries the information. The Wire Admin service will define what Consumer services will receive position information from what Producer services. It is therefore up to the administrator of the Wire Admin service to assure that only trusted bundles receive this information, or can supply it.