Friday, June 12, 2009


I am working on a web app, Direction+, running on Google App Engine for Java. Yes, it is another direction service that suggests a driving route based on your chosen source and destination. But it has some add-on features as its name suggests: Direction Plus.

First, you can personalise Direction+ by providing your car's information, in particular, the fuel consumption measurement of your car, for urban cycle, extra-urban cycle and combined cycle. Thus, when calculating the route, Direction+ is also able to calculate how much fuel you will use and how much it costs (based on the fuel price you set). The fuel consumption calculation is measured on each individual step of the route. For instance, driving on a motor way will be much more fuel-efficient than driving in the city center. Isn't it good to know the cost of the driving before hand? In addition, the calculation is done in your own browser and your personalisation is stored in your browser as a cookie. So there is no privacy concern at all.

Second, Direction+ is a mashup that combines Google Maps Service and BBC travel news service together. When a driving route is calculated, the travel news, e. g., accidents news, along the route are displayed as well on the map. Isn't it good to know the traffic situation before driving? Currently too many travel news are returned especially when the route is very long, efforts are being made to improve the algorithm of filtering the not-so-relevant news.

How quick is Direction+ updated with BBC travel news? Please see its status page. A complete update takes about 30 minutes. For instance, at the time of writing, the last update took 26 minutes to finish. It read 2297 news from BBC, among which only 50 happened after the previous update, and among the 50 news that newly happened, 12 have cached coordinate in the data store. So though the number of news is large, Direction+ manages to reduce the communication to a small amount.

One of the tricky things about GAE for java is that every servlet request must be served within 30 seconds. So the update of news is implemented in an incremental and on-the-fly way:
  • Incremental: the complete update is divided into many small steps, and each step can be finished in a controlled time slot;
  • On-the-fly: the news updated in each small step is available immediately, long before the complete update is done.
Direction+ is designed for UK users because I live in UK. Enjoy it and let me know what you think!

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