Integrating AJAX Approach into GIS Visualization Web Services Ahmet Sayar Indiana University Computer Science Department Pervasive Technology Laboratories February 24, 2006 ICIW’06, Guadeloupe, French Caribbean
Motivation & Contents
AJAX ( XMLHttpRequest Protocol )
Web Services ( SOAP Protocol )
AJAX+Web Services ( Why?, How? )
1. Overlaying map layers from Google and OGC WMS
Google + WMS
2. Plotting Geophysics data on the Google Map
Google + WFS
What Is AJAX?
A synchronous J avaScript a nd X ML is a combination of standard Web technologies –for the browser based web applications.
When done properly, it provides apparently seamless interactivity in browser clients.
No browser reloads
Much smoother than standard request-wait-response for browser forms.
Several Google tools are a very well known examples.
Google maps, Gmail, etc.
The real key is the standardization of the XMLHttpRequest Object
Key can be obtained from here http://www.google.com/apis/maps/
1 2 1 2
I - Google Maps + Web Map Service (WMS) GUI and SAMPLE OUTPUT Natural Gas Layer Electric Power Layer
II - Google Maps + Web Feature Service (WFS) Overlaying Geophysics data over Google maps OGC WFS + AJAX
Client has a LIGHT-MAPPING Service which makes image rendering. Data come from WFS in GML format.
WSDL is a Web service Interface Description Language encoded in XML.
Clients should prepare client stubs to be able to invoke the Web Services defined in WSDL.
Requests and returned GML data from WFS are put into SOAP envelope.
SOAP is an XML based message exchange protocol used in Web Services interactions.
Integration framework is needed Pure AJAX
II - Google Maps + Web Feature Service (WFS) GUI and SAMPLE OUTPUT Simple Architecture Supported Feature Data by the WFS Layer specific parameters for filtering
Good for the browser based Distributed SOA based applications.
Provides powerful interaction asynchronously.
AJAX and Web Services both use XML based message communication protocols. This enables application developers to easily integrate AJAX based browser applications into Web Services.
They leverage their advantages.
No need to modify or extend any technologies in the AJAX model or Web Services.
Users do not need to wait whole data to be received to render and display the results. Partial displaying is possible without refreshing the whole page. Instead of making request for whole page, only the interested part will be requested. This reduces the workload of the network traffic.
Advanced XML structured geo-data parsing. Fast and efficient compared to DOM parsing.
Introduces some extra work. Extra work mostly comes from the conversion of parameters to be able to make compatible requests to remote Web Services. In order to make valid requests, the proxy server should be deployed locally and client stubs for Web Service invocations should be created before running the application.
The performance is degraded by the intermediary proxy server for the conversion and message handling jobs.