Open-Source GIS

Abstract

The chapter explains the components of which an Open Source GIS is built of. They comprise the core software-component (mapserver), open source geospatial libraries, a typical open source GIS (Quantum GIS), the presently most widely spread open source database (PostgreSql) including its geospatial extension (PostGIS), and an overview over the most important license models. A mapserver can broadly be defined as a software platform for dynamically generating spatially referenced digital map products. The University of Minnesota MapServer or UMN MapServer, or simply MapServer, is one such system. Its basic features are visualization, overlay, and query. The mapserver architecture consists of a client, a server, and a database. The server is split up in three layers, the CGI-layer tying in to the network hardware, the geospatial analysis system, and the communication layer. Client and server do a load balancing for an optimal performance. The architecture is built upon the standards of the Open Geospatial Consortium of which those regarding interoperability are most important. The section concludes with a number of examples. The following section names and explains many of the geospatial open source libraries, starting with GDAL (raster) and OGR (vector). The other libraries are FDO (Feature Data Objects, JTS Topology Suite (JTS), GEOS, JCS Conflation Suite (JCS), MetaCRS, and GPSBabel. The application examples include derived GIS-software and data format conversions. The following section provides a detailed explanation of Quantum GIS, its origin and its applications. The features include a rich GUI, attribute tables, vector symbols, labeling, editing functions, projections, georeferencing, GPS support, analysis, and Web Map Server functionality. The architecture of Quantum GIS comprises a hierarchical set of several layers that ranges from data access via analysis to application. Future developments will address mobile applications, 3-D, and multithreading. The next section is dedicated to the database part. The origins of PostgreSQL are outlined and PostGIS discussed in detail. It extends PostgreSQL by implementing the Simple Feature standard. This allows applying a rich set of geospatial functions such as geometry types, e.g. polygons, relationships, e.g. within, and analysis function, e.g. convex hull. The last part of the chapter explains the most important open source licenses such as the GNU General Public License (GPL), the GNU Lesser General Public License (LGPL), the MIT license, and the BSD license, as well as the role of the Creative Commons.