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Open Source and free GIS: A way out?
THE TOOLS
Interoperativity and data conversion In the GIS sector, pressure for having fully interoperative software has always been strong; as a result, the use of different data sources (with or without the need for conversions) does not pose major obstacles also for free software. The basic tool for this is the library GDL/OGR (hereafter GDAL; http://www.gdal.org), that allows all major free programs to use a wide variety of data, both raster and vectors (Tab.1). Among the few problems that remain, the most serious is with AutoCAD files (dwg); in this case the conversion requires a library (OpenDWG) available at no cost (for non-commercial use), but non-free (in spite of its name). Although technically easy, this makes it illegal its redistribution when linked to FOSS programs; every user (or group of users) is therefore requested to the necessary programs with the support to OpenDWG). Reprojection of rasters and vectors among different coordinate systems and datum are managed by the PROJ library (http://www.remotesensing.org/proj). The precision is the same as for major commercial software, and may be increased (thanks to the availability of source code) with slight adaptations of the existing code. Geodatabase The killer GFOSS application in this sector is undoubtedly PostGIS (http://postgis.refractions.net), linked to the GEOS library (http://geos.refractions.net). It is a spatial extension of PostgreSQL, the most powerful FOSS relational database. PostGIS allows the storage and management of geographical vector data directly from within the database (thus using standard SQL and its Open Geospatial Consortium [http://www.opengeospatial.org; hereafter OGC] extensions: distance, area, buffer, overlay etc. Every record is associated to a specific projection, thus in the same database data in different projections can coexist, and they'll be correctly overlayed. The data model is non-topological, and fully compliant to Simple Feature specifications of OGC (SFS 1.1, SFS TF 1.1). Importing and exporting ESRI shapefile data is straightforward. Raster geodatabase are not available for now, but there are plans for a future implementation. Desktop mapping The vat majority of so-called GIS work is indeed desktop mapping. In this respect, GFOSS had a significant gap compared to commercial applications, because most GFOSS users were IT persons, more inclined toward problem solving than to graphical appearance. In the last few years, thanks also to a larger user base, the situation has vastly improved, especially thanks to the rapid evolution of QuantumGIS, or qgis (http://qgis.org), a point-and-click application not dissimilar from commercial equivalents (see Fig. 1).  Figure 1 QGIS can display and edit various raster and vector geodata, including GRASS layers Among the strong points are:
Other desktop GIS are available, including Thuban (http://thuban.intevation.org) and OpenEV (http://openev.sourceforge.net); the first one has strong limitations in the handling of rasters, while the second, powerful in the image analysis, is not as easy for the unexperienced user. Geographic analysis The “all purpose” free is GRASS GIS (short for Geographic Resources Analysis Support System: http://grass.itc.it). Historically known as a raster GIS, difficult to use, mainly command-line oriented, since 2002 it has known a heavy development; the 2D and 3D vector section, as well as the database integration, have been completely rewritten, and it is now available as a new (6.0) stable version. It is very complete, with all functions required for a professional use, from management and analysis of geospatial data to image analysis, from chart and maps production to spatial modelling and 2D, 2,5D, and full 3D visualization; a complete list of the >350 modules (many of which with several options, giving a total of more than 600 commands) can be found at: http://grass.itc.it/grass60/manuals/html60_user/index.html; in addition to the command shell, fundamental for automatizing the work flow, it has a simple and effective graphical interface (Fig. 2), although QGIS is becoming the best tool for this. It is very easy to combine existing commands, creating your own scripts, in addition to the possibility of programming more complex tasks in C, C++, Perl etc. Alphanumeric data can be managed with a variety of tools, among which the simple DBF, and the powerful relational database PostgreSQL. Statistical analyses can be run smoothly from within a GRASS session, both with GRASS internal modules, and with R statistical package (http://www.r-project.org).  Figure 2 GRASS and its native graphical interface. Hundreds of modules and commands are accessible trough pull-down menus When compared to commercial equivalents, GRASS is generally very stable, also in very large and complex applications; its usage may be sometimes a bit tricky for the inexperienced user (thus the importance of the QGIS interface). Web mapping The Web is, and it has always been, the domain of free software; no surprise then that the one of the most powerful web mapping application is a free one; Mapserver (also called UMN Mapserver: http://ms.gis.umn.edu) has been developed originally by the University of Minnesota. It is OGC compliant (WMS 1.1.0, WMS 1.0.0, WMC 1.0, WFS 1.0.0, SLD 1.0, GML 2.0, Filter 1.0.0, WMS 1.1.1). The developers have been careful not to overfeature the main engine, that is very stable even in critical applications; a number of applications have been built on to of it, extending its functions by the use of various programming languages: php, perl, python, javascript, etc. Examples include pmapper (http://pmapper.sourceforge.net), Chameleon (http://chameleon.maptools.org) and Cartoweb (http://www.cartoweb.org). With these tools, customized web mapping applications can be built in a very cost-effective way. GPS Global Positioning System receivers are very useful and widespread; many free programs are available for interacting with GPS hardware, from single-purpose command-line downloading programs (e.g. gpstrans: http://gpstrans.sourceforge.net) to the more sphisticated ones, with graphical interface and conversion tools (e.g. gpsbabel: http://gpsbabel.sourceforge.net); some have real-time navigation application (e.g. gpsdrive: http://www.gpsdrive.cc) or differential correction (dgpsip: http://www.wsrcc.com/wolfgang/gps/dgps-ip.html). The easy integration among different tools, characteristic of open source programs, allows larger programs like GRASS and QGIS to – and upload points and tracks straight from/to the devices. In the case of GRASS, data are reprojected automatically in the working projection and converted to the GRASS vector format. Java: another world? The power of Java programming language has allowed the development of GFOSS applications. The growing computing power of modern PCs makes speed of Java programs sufficient, even for heavy applications. Java, however, is not free as a language, and its proprietary alone (Sun Microsystems, Inc.) has the right to change its specifications; this makes it less attractive for FOSS people (see e.g. http://www.gnu.org/philosophy/java-trap.html). In spite of this, a few Java GFOSS programs are particularly interesting; Deegree (http://deegree.sourceforge.net) is a good MapServer, fully compliant with OGC specifications (WTS 0.5, WMS 1.1.1, WMS 1.1.0, WMS 1.0.0, WMC 1.0, WFS 1.0.0, WCS 1, St Cat 0.06, GML2.1 2.1.2, Gaz 0.8). For desktop mapping ans some analysis, Java Unified Mapping Platform (JUMP: http://www.vividsolutions.com/jump) has attractive features (Fig. 3). For GRASS users, a Java graphical interface is also available (JGRASS:http://www.hydrologis.com/html/jgrass/jgrass_en.html).  Figure 3 GRASS can display and analyse 2,5 and 3D data |