I started to realize this big change of GIS awareness when I watched the CNN news in September 2005 after the Hurricane Katrina. The director of Federal Emergency Management Agency (FEMA) in U.S. told the CNN reporters specifically that the FEMA rescue efforts are heavily relying on GIS technology. It is so sad to realize that after we loss hundreds of thousands human being lives (in the Tsunami event) and billions of dollar’s damages (in the Hurricane Katrina event). These tragedies started to create the GIS awareness for our general pubic and everyone begins to understand that GIS is a vital technology for our society. The Figure 1 shows a screen shot of the Google Earth Pro with the GIS data indicating the RedCross Shelter’s location and capacity for the Hurricane Katrina relief efforts. The Second Big Change: New Computing Technologies for Internet GIS.The second big change in Internet GIS is the adoption of new technologies in the Internet GIS market, especially for the development of AJAX (Asynchronous JavaScript and XML) and image tiling techniques for Web-based 3D visualization. Traditional Internet GIS applications and Web-based mapping tools are always suffer from the slow response and the lack of high resolution images because of the limitation of image data sizes and the client/server communications. The two new technologies (AJAX and image tiling) can improve the performance and repose times of Internet GIS application significantly. Strictly speaking, the two new technologies have been existed for a while long before Year 2005. However, the combination of the two technologies has not been seen until the early 2005. [maps.search.ch] and [maps.google.com] are the two early examples of Internet GIS applications which adopt both AJAX and Tiling techniques together. Amazon’s [maps.a9.com] is also a good example of AJAX applications with a very interesting “Street Block View” function. Microsoft also has its own AJAX map application [virtualearth.msn.com]. AJAX is not a single technique but a combination of multiple web techniques for creating fast response, interactive web applications. AJAX can send user’s requests to the web server to retrieve only the data needed by the request. Therefore, the total amount of images or data interchanged between the client browser and web server will be reduced significantly. For example, if users need to zoom-in to a new map area in a Web map browser, the server will not need to reprocess the whole Map page content but only to re-send the smaller area of map requested by the user. By using Simple Object Access Protocol (SOAP), JavaScript, or similar XML-based web service protocols, AJAX applications can have very responsive actions from users’ side. One unique advantage of AJAX is the key word “Asynchronous”. According to the first AJAX paper (wrote by Jesse James Garrett “An Ajax application eliminates the start-stop-start-stop nature of interaction on the Web by introducing an intermediary — an Ajax engine — between the user and the server. It seems like adding a layer to the application would make it less responsive, but the opposite is true. Instead of loading a webpage, at the start of the session, the browser loads an Ajax engine — written in JavaScript and usually tucked away in a hidden frame. This engine is responsible for both rendering the interface the user sees and communicating with the server on the user’s behalf. The Ajax engine allows the user’s interaction with the application to happen asynchronously — independent of communication with the server. So the user is never staring at a blank browser window and an hourglass icon, waiting around for the server to do something.”(Cited from http://www.adaptivepath.com/publications/essays/archives/000385.php). Figure 2 illustrates the synchronous interaction pattern of a traditional web application (top) compared with the asynchronous pattern of an Ajax application.  Figure 2: The synchronous interaction pattern of a traditional web application (top) compared with the asynchronous pattern of an Ajax application (bottom). (This image and caption are cited from the on-line Adaptive Path paper: Ajax: A New Approach to Web Applications, by Jesse James Garrett (original URL: http://www.adaptivepath.com/publications/essays/archives/000385.php The second major technique used in the Internet GIS is the image tiling for Web-based 3D visualization. The introduction of tiled images is to improve the application performance by allowing the application to process an image region within a number of tiles without bringing the entire image into computer memory. Many early Web image applications have adopted this method for a while. In early 2005, several Internet GIS applications (such as Google Earth (http://earth.google.com) and GeoFusion (http://www.geofusion.com/) started to improve the image tiling techniques for their 3D visualization tools and created an interactive, fast-performance virtual reality in a digital earth form. Users can overlay aerial photos, satellite images with digital elevation model (DEM) to visualize the 3D spatial information. Different companies have their own “secret” technologies, such as wavelet transform, component mixing, quantization, or entropy coding, in order to boost the performance of the 3D visualization Figure 3 shows an example of image tiling technique. The large size image is first shrunk down to different resolutions for building multi-level image pyramid layers, and then each layer is further broken into small tiles in a separate file with a standard naming convention related to the specific tile position. The tiles are typically same size squares except for the right and bottom side, because the image width and height may not be exactly the integer multiples of the tile width and height. In order for fast retrieval of the necessary tiles upon request, the adjacent tiles in the same layer are normally named in sequential order. Thus the entire tile-based pyramidal data are stored in a hierarchy, indexed format at the server-side database (Figure 3).  To represent the reality, users typically only see part of the image on the fly instead of the whole one. The adoption of tiling technique is to aid the presentation of very high resolution imagery and halts the unnecessary work on off-screen sections. This prevents the memory overload, decreases processing and bandwidth requirements, and making it possible to move quickly from one section of the image to another. By combining both the AJAX and image tiling technologies, the Internet GIS application developed in 2005 have much faster performance and interactivity comparing to the traditional Internet mapping or Web-based GIS tools. This is critical for the general public because more people will start to use Internet GIS because of these improvements. |