Use GPS And Web Maps For Location-Aware Apps

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Det nævnte kan også lade sig gøre med Virtual Earth Web Service ...
/Sik

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You can also us Virtual Earth Web Service in the mentioned examples ...

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Christopher Mitchell

The location-aware application is made up of two chains of functions. The first is the system that monitors the current tasks and issues, as shown in Figure 2. Tasks are stored in a SQL Server  Compact database table. In addition, a set of auxiliary data is stored within another table called geocache. Using the separate table is a means of limiting the amount of connectivity required, as I will explain later in this article.

Figure 2 Monitoring and Alerting of Location-Aware Tasks

The information for the points nearby is provided by the Micro soft MapPoint Web service. There are different data sources in the MapPoint Web service for different parts of the world, and some have more capabilities than others. The data source used by the sample application is NavTech.EU. Once this information is gathered, some distance calculations can be performed and alerts issued, where applicable.

The second chain of events (see Figure 3) adds tasks to the Tasks list on your Windows Mobile device via the POOM. This framework also allows access to the calendar and SMS functions.

Figure 3 System Flow for Adding Tasks to the Wheretodo Application

Tasks and Cache represents the first part of the monitoring and alerting chain of events. The task manager simply gets a list of tasks from the POOM. It also manages the geocache, which addresses the issues with using Web services on potentially limited connectivity devices. The level of connectivity of the device can range from permanent connectivity to sparsely connected or no connection at all.

To cope with the large range of connectivity strength, you need a decent cache policy for the Web service data and a straightforward system that knows how to make the most of the connectivity. Although very complex scenarios could easily be imagined, a simple radius cache policy was established for the purpose of this article. For example, a query is placed to the MapPoint Web service looking for all Chinese take-out restaurants within a given radius from the current location, say 80 kilometers (km). Once you have gone 40 km in any one direction, a new search is issued. This is based on the principal that every query to the Web service is costly.

It also makes the assumption that the distance you travel away from the point where you entered the task is not likely to be greater than 40 km. As the distance used to control the actions of the cache is likely to vary from person to person and country to country, it is designed to be input by the user.

Logs of where queries have been run are stored in the geocache log database and checked before any additional queries are made so that duplicate information is not requested from the Web service. It also provides the opportunity for the system to be pre-populated with a considerable volume of information. [...]

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Read more: http://msdn.microsoft.com/en-us/magazine/2009.01.wm6gps.aspx

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