| Technotes-
The Building of a GIS for Internet Users
By Brian Massey In 1996, Japan's Ministry of Health and Welfare (MHW) challenged Mitsubishi to develop a geographic information system (GIS) that would serve government employees at all levels-municipalities, prefectures, and the ministry itself. In all, 7,000 employees would use this system. The system was to manage a seamless base map that covered the entire country at 1:25,000 scale, and eventually 1:2,500 scale. The base map would consist of intelligent layers, include political boundaries, transportation, waterways, land use, and key building footprints.
The system had to make use of an existing infrastructure including PCs of all configurations and the government's existing Intranet. Furthermore, MHW was unwilling to expend the cost of installing and maintaining a large central GIS server system. A single Microsoft Windows NT server was allocated. The system, called the Health Medical Welfare Information System, was to provide detailed analysis of the MHW databases of Japanese disease, aging, and mortality rates against information such as demographics and medical facility infrastructure. By understanding the effectiveness of their health delivery infrastructure, municipalities and prefectures can better plan for expansion and change.
A team of companies worked to complete the system including Mitsubishi Corporation, Justec Corporation, and TechnoGroup, an international consortium of companies. Soft Reality, Inc. (Austin, Texas), a member of TechnoGroup was tasked with creating the network delivery and display technology. Justec Corporation was primarily responsible for creating the applications that the government employees would use. Soft Reality realized that it would need to create a system architecture specifically for Internet transportation of data, scalability, and ease of use. The result of this effort is Soft Reality's EarthKeyª. EarthKey is a development platform that simplifies the creation of network enabled mapping applications. Version 2.0 of EarthKey was released in November 1998 and version 3.0 is currently in development. Turning the Internet GIS Upside Down
Existing geographic information systems have been built on a large centralized architecture. Even with the advent of desktop GIS, these systems remain relatively expensive and difficult to use. All of the major GIS software vendors have added Internet access tools to their systems. However, the work of processing geospatial data is done on the central servers. Thus, they cannot be scaled effectively to meet the needs of a large number of users. In the world of the Internet we call this a "fat-server/thin-client" system.
EarthKey makes use of the users' computers to do most of the work of processing the data. This frees the server from most of the tasks of displaying images, processing user interaction, and performing spatial queries. EarthKey has a "thin-server/fat-client" architecture.
The thin-server/fat-client architecture of EarthKey is designed to support powerful geospatial applications that can be delivered via the Internet. A quality control engineer should be able to modify a drawing on-line. An oil field engineer should be able to calculate sub-surface contours based on existing well logs. A real estate agent should be able to select properties on a map and have tax records appear in a spreadsheet for analysis. These tasks are not available to users of Internet map publishing systems. The Data
EarthKey data sets are pre-sorted and highly compressed without loss of accuracy. The challenge for a thin-server/fat-client system is getting the data to the client for processing-especially if you are working with the small pipes of the Internet. EarthKey accomplishes this with a unique file format called the Internet Graphics Data (IGD) format. In IGD files, map data is stored in sections. This means that a coverage is stored as a number of small sections, any one of which can be read, transmitted, and then re-assembled somewhere else. This is important for the Internet because it allows EarthKey to transmit only those sections of a map needed to complete a view. Furthermore, the sections of an IGD file are pre-sorted spatially. Pre-sorted data makes spatial queries fast and efficient.
Geospatial coverages aren't getting any smaller, and EarthKey IGD files are designed with this in mind. The files are highly compressed and optimized for storage of point/line/polygon data. They also support raster information in a variety of compressed forms, including JPG, TIF, BMP, and MrSID Portable Image Formatª. Each IGD file represents a meta-layer than can contain multiple layers within. A number of attributes are available for any object. These attributes define the default display properties-color, line style, fills-as well as user-defined keys that can be linked to database data. Soft Reality provides a suite of tools called the Map Manager Toolkit that extracts data from existing formats and creates an IGD file database for Internet distribution. The Server
The key idea behind the EarthKey Server is that it does little more than efficiently stream data to client applications. This strategy allows many users to be supported by relatively inexpensive servers. The role of the EarthKey Server is to respond to requests from client applications across the Internet, to find the proper IGD file sections that are needed, to compress the data stream, and to send the information on its way. After that, it can move on to the next user. In implementation the EarthKey Server is a multi-threaded Information Server Application Programming Interface (ISAPI) extension for Microsoft's Internet Information Server. An ISAPI extension runs as a part of the Web-server and is very efficient with server resources. Client Applications
With the EarthKey Server doing so little, the bulk of the work falls to the EarthKey Explorer client. The EarthKey Explorer is a 32-bit component optimized for Microsoft Window's operating systems. The component is a basic GIS capable of very powerful analysis and user interaction.
The most striking thing about an EarthKey application is the way it displays highly detailed maps and images with silky smooth pans and zooms. This is a marked change from the slow refreshes of most Internet mapping packages. Of course, there is a pause when you move to a new area of the map as data is downloaded from the server. Once the data is downloaded moving around the map is fast and effortless.
The EarthKey Explorer component provides the following services: 1) seamless communication with an EarthKey Server, group of servers, or the local file system; 2) caching of IGD data on the user's system, so data is only transmitted once; 3) map display with high-speed picking, panning, and zooming; 4) full featured development API which allows for a high level of customization; 5) spatial querying; and 6) complete drawing and editing facilities.
EarthKey Explorer is a Component Object Model (COM) object. Applications can be built using Visual Basic, Visual C/C++, Delphi, Java or any 32-bit COM compliant environment. You could even drop an EarthKey Explorer into an Excel spreadsheet.
The thin-server/fat-client architecture of EarthKey is ideal for implementing Internet-based GIS. It is designed to support many users, large detailed map bases, and powerful geospatial analysis tools. EarthKey 2.0 is currently available from Soft Reality, Inc. About the Author:
Brian Massey is co-founder and Vice President of Customers for Soft Reality, Inc., Austin, Texas. You can reach him at [email protected]. Soft Reality is a network graphics consulting company. More Info Ministry of Health and Welfare www.mhw.go.jp Soft Reality, Inc. 9801 Anderson Mill Rd., Suite 209 Austin, Texas 78750 512.336.8500 Fax: 512.336.8700 www.earthkey.com Soft Reality Confidential August 30, 1999 Back |
