A webgis is a system to manage and deploy spatial data and associated
attributes on the web. Usually, the data are static on the
client-side: a standard webgis application doesn't manage dynamic
information. In this article we illustrate a dynamic webgis: a system
architecture that is able to automatically collect, manage and display
dynamic geographic information. In this way one can monitor in real
time on the map the state of time-evolving entities. Possible
applications are fleet tracking, environmental control, surveillance.
Actually the system is being applied to fleet tracking.
In a standard webgis, once the client has requested and received data,
these data can change on the client, if and only if, the client send a
new request to the server (common HTTP protocol behavior). The main
drawback of this kind of architecture is that every time the user
wants to change or interrogate the map, the server has to update the
view and send it to the user. This can create an impression of poor
interactivity, but this architecture is not able to show the state of
an entity after it is changed.
It is our opinion, that in a dynamic architecture, the changes should
be visible, to the user, in real-time. We mean, for dynamic webgis,
an environment where the entity state can change many times. If one
has to monitor the state of an entity (eg. temperature or alarm sensor
in a building), there is the need of managing dynamic information, in
a more responsive way. Our aim, here, is the proposal of a dynamic
architecture consisting into a real-time webgis where the user can
observe changes over the map as the corresponding information is
available and updated from external sources, without explicit requests
by the user.
The developed system, termed USAlov, is based on Alov /
TimeMap. TimeMap is developed in J2EE technology and it is very
flexible and easily extensible. USAlov is a J2EE / J2ME application
developed to track locations of remote mobile devices storing their
positions on a relational database. It can be used to view real-time
locations of mobile devices.
Our mission has been the integration and development of new features
in Alov / TimeMap. We have added a tracking server, and a mobile
component, while the applet has been extended with modules for monitor
the state of targets.
Tracking server is a new server-side component, that manages dynamic
information about mobile devices. It stores this data into a MySQL
database, and stores in memory the information about active devices.
We have developed a mobile component that runs on mobile devices and
communicate, by the bluetooth protocol, with common GPS receivers,
and, by GSM network, with the tracking server. Last, we have extended
the basic TMJava applet, used to view static GIS data, with the
capability to communicate with tracking server and show dynamic
information. The extended applet allows to dynamically query the
tracking server, to get the position of the mobile devices
The mobile device, J2ME enabled (eg. mobile phone), communicates with
a GPS receiver, and it sends information about its location to a web
server. Thanks to GPRS / UMTS connection and short size (few bytes)
messages it is possible to use this application in a not expensive
The server stores the messages from mobile devices into a database and
in an active structure that resides in the server. A thread is
responsible to load information about monitored targets in memory.
The client is based upon Sun Java applet technology, which allows to
view the whereabouts of an entire fleet from a desktop. The applet
provides a tracking panel used to configure the request to send at
tracking server. After query, the client runs a thread that updates
the requested data at configurable intervals time. Indeed, the applet
is in a continuous polling to the server with HTTP requests.