SAGA - Entwurf, Funktionsumfang und Anwendung eines Systems für Automatisierte Geowissenschaftliche Analysen

The System for Automated Geoscientific Analyses (SAGA), which is in the focus of this work, originates from the practical need to develop new methods for the analysis of spatial data and to apply them immediately. To efficiently support the work in research projects a number of demands has been outlined and successively been implemented.An application programming interface (API) forms the system"s foundation and supplies particularly the programmer of methods with a comfortable object model for the processing of raster as well as vector data. Methods are placed as modules in dynamically loadable program libraries, which are separated from the core system. Due to this modularisation a parallel and independent development of methods by different programmers becomes possible, which e.g. enables a splitting of development tasks in larger projects. For the execution of modules the system offers currently two alternative user interfaces. The graphical user interface (GUI) allows to a large extent an intuitive usage of the system. Besides the execution of modules its tasks include the management and visualisation of spatial data. The second user interface is a command line interpreter (CMD), which has been designed exclusively for module execution. The CMD can be executed from a script file, so that a further automation of complex work flows, which are composed of different successive calls to modules, becomes possible.The implementation of the systems has been done using the wide spread object oriented programming language C++, which on the one hand gives an extensive control over the computer management and therefore allows diverse optimisations and performance gains. On the other hand C++ supports a structured programming by the construction of easily usable object models. Besides object models for spatial data the SAGA-API offers numerous helpful functionalities for the programming of modules, e.g. for solving mathematical problems or for the creation document files. Operating system specific functions are accessed using the platform independent C++ class library wxWidgets. Therefore SAGA works under Windows as well as Linux operating systems.The system"s core, consisting of API, GUI and CMD, as well as numerous modules have been published together with their source codes under a Free Open Source Software (FOSS) license. Source codes, executable programs and further information about the system can be obtained from the internet site at http://sourceforge.net/saga-gis. The free availability itself aroused a broad interest among users, who have to deal with spatial data, and the opening of the sources and the efficient design of the API resulted in a positive feedback of the young SAGA user community.Currently there are about 230 modules included in the free available SAGA distribution. The spectrum of methods covers simple tools as well as complex analyses and simulation models. Modules for the data import and export enable the data exchange with other software. Fundamental capabilities are modules for the projection of spatial data into different coordinate systems. Many standard functions are provided for the work with tables, raster and vector data. But besides the general processing of raster data, the methodological focus has to be seen in the modules for terrain analysis and geostatistics, which point back to the origin of the SAGA development, when it was the objective to derive terrain parameters and classifications based on digital elevation models for the support of soil mapping. This was the starting point for a rapid development of a wider methodological framework, which lead from the terrain based modelling of processes to the regionalisation of soil properties with the help of geostatistical procedures. Since then SAGA and its implemented methods form a basis for the successful execution of various research projects. But SAGA proved itself for educational purposes too, not at least because it is a free of charge alternative to comparable commercial software.