A CARTOGRAPHIC WEB CLIENT TO EXPLORE REMOTE GI METHODS
Recently, the diffusion of GIS methods on the Web through Web Services has undergone a significant acceleration. Whereas Location Based Services are meant to be controlled from mobile applications, newly available methods are often to be chosen and invocated from human end users. These can be members of a research platform community or end users with no specific expertness. In both cases, users should be able to explore the remote methods provided by the Web Service preliminary to conveniently call them in their data derivation workflow.
The objective of our work is the exploration of remote methods from a cartographic Web client embedded in a Web browser. We focus on :
- parameterising a method call –or a sequence of method calls- and visualising the result.
- possibly stepping back, trying another call, and comparing the results.
These functionality though looking simple are still challenging as explained in the paper.
Our proposal is a cascading Model-Viewer-Controller architecture : server model to web model to cartographical viewer.
The server model is composed of GI data and methods hosted on a complex platform on a server. Single method calls and complex structures of method calls are represented as activities.
The Web model is composed of objects that represent, within the client, server information that need to be manipulated on the client but that cannot be transferred as such on the client. For instance feature collections are represented as SVG documents. Defining the frontier between the server model and the web model, as well as synchronising them can be made in different ways. We tried to adopt a flexible server-to-web-model architecture to adapt this frontier to the type of method and data. Indeed, depending on the size of the data collection and of the method complexity, some operations can be transferred as such on the applet or only their metadata can. A key aspect is the synchronisation of the ‘session history’ which is represented by an activity on both sides.
The cartographic view is composed of graphical interactive widgets displayed on the client interface to represent web model components (e.g. a SVG map). Visualising a result of a method call requires introducing a new type of legend to display lineage information of the form ‘this object has been derived from this one through this method call’ and to support visual assessment of a method effects.