Since 1999 the OpenGIS Consortium (OGC) has been researching the feasibility of heterogeneous ‘open’ GIS systems that achieve interoperability and break with a history of proprietary ‘closed’ GIS technology. The aim of the OGC Web Mapping Testbed Phase 1 (WMT1) was to “increase users’ ability to access and overlay maps and earth images available form other vendor’s Web map servers. Within this and the subsequent OGC Testbeds, many data providers and curators have successfully combined disparate data and systems via the Internet.
Following an active involvement in the Web Mapping Testbed since it’s inception, Cadcorp introduced support for the OGIS Web Server as part of Cadcorp SIS V5.2 Map Modeller in 2000. Now, with the release of Cadcorp SIS – Spatial Information System V6, this has been enhanced to include three servers: Web Map Server (served rasters), Web Feature Server (served vectors) and Web Terrain Server (served 3D images). All are included as standard as part of Cadcorp SIS Map Modeller package and once again this rich support for OGC interfaces places Cadcorp at the leading edge of OpenGIS implementation.
Cadcorp SIS Web Map Server offers users the capability to quickly and easily serve maps on the Web in the form of rendered raster images. This means that Cadcorp SIS can be used to create maps which can then be easily distributed around an organisation and even its customers with images of any of the 50+ formats it supports ‘out of the box’.
To create and serve these maps, only three parts are required: a map, a server and a client. A map, (saved in Cadcorp SIS as a Saved Window Definition or SWD), is produced using either Cadcorp SIS Map Manager, Map Editor or Map Modeller. To then serve a map on the Web, Cadcorp have used the Internet Server Application Program Interface (ISAPI) to create the SisIsapi.dll. This is a dynamic link library (dll) that contains a set of Microsoft Windows program calls. It allows a user to access a Web server using any standard web browser, request map information, get that information back and see it displayed on their Web page or within Cadcorp SIS itself running as a client.
With the SisIsapi.dll it is possible to set up a web server that can perform the following tasks:
-Display a map in any standard browser without need for plugin’ software.
-Display in a browser a list of available maps stored on the server.
-Display a map window with basic information about the content of the file, such as the list of overlays within it and its scale. It also provides the possibility to perform basic zoom and pan commands and provide information in XML format about the SWDs found with additional information, such as their name, current extents, scale and projections.
-Cadcorp SIS – Spatial Information System user interface to connect to an OpenGIS Web Map Server as a client. The same principles are applied to serving vectors and 3D images using the same SisIsapi.dll.
Cadcorp SIS therefore provides all three OpenGIS servers ‘out of the box’ with the Map Modeller package at no extra cost. Whilst standard HTML browsers can be used as clients, Cadcorp SIS itself can also act as a desktop client adding significantly to the flexibility and possibilities of deploying these low cost OpenGIS Web Server implementations in an organisational setting.
