A BETTER OPTION FOR SPATIAL ANALYSIS
“A geographic information system is a facility for preparing, presenting, and interpreting facts that pertain to the surface of the earth. This is a broad definition. , a considerably narrower definition, however, is more often employed. In common parlance, a geographic information system or GIS is a configuration of computer hardware and software specifically designed for the acquisition, maintenance, and use of cartographic data” (C. Dana Tomlin, 1990). Almost all human activities and decisions involve a geographic component. One cannot get away from the location issue, and understanding the geography around us and its importance, is essential to ones everyday life. Working with geographic information involves complex and difficult choices that are unique. Although much geographic information is static, the process of updating is complex and expensive. GIS is one of many information technologies that have transformed the ways geographers conduct research and contribute to society. GIS have emerged as very powerful technologies because they allow geographers to integrate their data and methods in ways that support traditional forms of geographical analysis. With GIS it is possible to map, model, query, and analyze large quantities of data all held together within a single database.
GIS software is a vital component of an operational GIS. The key parts of any GIS software system are the user interface, the tools or functions, and the data manager. All three parts may be located on a single computer, or they may be spread over multiple machines in a departmental or an enterprise system configuration. There are different types of GIS software like desktop, Web mapping, server, virtual globes, hand held and other. Software may be licensed using a commercial or open source model. In the early days open source software products provided only rather simple, poorly engineered tools with no user support. Today there are several high-qualities, feature rich open source software products.
The free and open source software “movement” has significantly impacted all aspects of information technology (Tiemann, 2009). We, as GIS educators, are already using many open source software packages daily and may not be aware of them. QGIS is the best GIS tool in the free and open-source software (FOSS) community. It is a user friendly Open Source Geographic Information System licensed under the GNU General Public License. Unlike traditionally expensive proprietary software, QGIS is a viable prospect for anyone with basic access to a Personal Computer. As an official project of the Open Source Geospatial Foundation, it runs on Linux, UNIX, Mac OSX, Windows and Android. Using open source software also means you are not locked into using a particular vendor’s system that only work with their other systems.
QGIS is widely believed as the best open source software with stunningly beautiful options for labelling objects. First of all, it is offered for free and one doesn’t require to pay at all. It is developed to be accessible to anyone and has got very fast fixes for bugs and security exploits, with very fast upgrades to new releases. it is all volunteered, from all over the world, so at any given time there are thousands of people looking at the source code to find or fix a problem with the software. Secondly QGIS offers multiple options for any given task. Unlike a proprietary software vendor, it offers support that fits our specific needs and is available when we need it.
The QGIS Browser applications help many manage their raster, vector and GIS data. They give basic preview functions but the focus is on data access and organization. QGIS’ Composer on the other hand has the ability to create an “Atlas” built-in, and it works very well. QGIS Server provides a web map service (WMS). The WMS uses the same libraries as the desktop application. Maps and print templates created in QGIS desktop can be published as web maps simply by copying the QGIS project file into the server directory.
QGIS aims to be an easy-to-use GIS, providing common functions and features. The initial goal was to provide a GIS data viewer. Now a day QGIS offers many common GIS functionalities provided by core features and plugins. One can view and overlay vector and raster data in different formats and projections without conversion to an internal or common format. Supported formats include:
- Spatially-enabled PostgreSQL tables using PostGIS, vector formats supported by the installed OGR library, including ESRI shapefiles, MapInfo, SDTS and GML.
- Raster and imagery formats supported by the installed GDAL (Geospatial Data Abstraction Library) library, such as GeoTiff, Erdas Img., ArcInfo Ascii Grid, JPEG, and PNG.
- GRASS raster and vector data from GRASS databases (location/mapset),
- Online spatial data served as OGC-compliant Web Map Service (WMS) or Web Feature Service (WFS).
QGIS uses the GDAL/OGR library to read and write GIS data formats. Over 70 vector formats are supported in QGIS. Besides, in QGIS, one can create, edit, manage and export vector maps in several formats. Raster data have to be imported into GRASS to be able to edit and export them into other formats. QGIS offers the following:
- digitizing tools for OGR supported formats and GRASS vector layer,
- create and edit shapefiles and GRASS vector layer,
- geocode images with the georeferencer plugin,
- GPS tools to import and export GPX format, and convert other GPS formats to GPX or download/upload directly to a GPS unit,
- manage vector attribute tables with the table manager plugin.
We can also perform spatial data analysis on PostgreSQL/PostGIS and other OGR supported formats using the ftools python plugin. QGIS currently offers vector analysis, sampling, geoprocessing, geometry and database management tools. One can also use the integrated GRASS tools, which include the complete GRASS functionality with more than 300 modules.
The QGIS semi-automatic classification plugin lets you download Landsat imagery and classify them in a semi-automatic way. The Orfeo toolbox delivers a range of tools to filter process and manipulate raster data. LASTools can be integrated to handle LiDAR. The Semi-Automatic Classification Plugin also allows for the supervised classification of remote sensing images, providing tools for the download, the preprocessing and postprocessing of images. Search and download is available for ASTER, Landsat, MODIS, and Sentinel-2 images. Several algorithms are available in QGIS for the land cover classification.
Image.1. QGIS GUI with Landsat 8 Image and Processing Toolbox with a multitude of processing options to the left.
The most important advantage of QGIS lies in its ability to adapt to our special needs with the extensible plugin architecture and libraries that can be used to create plugins. It seems to be evident that QGIS is actually more algorithm-rich than any other off-the–shelf proprietary software, at least at present. For example, SAGA has many terrain analysis algorithms built-in than does the Spatial Analyst extension in ArcMap. In ArcMap, it would often require us to essentially build the algorithms ourself as a chain of geoprocessing tools that use primitive map algebra operations. But it’s very nice to be able to calculate, for example, topographic position index (TPI) directly in QGIS via SAGA. There is another advantage for QGIS with respect to Geographic research: ESRI’s algorithms are “black-box”, in that one can’t find out exactly how some operation was done. With QGIS, we can actually read the code, so we can know exactly how some algorithm is implemented, which is important for academic integrity. The accelerating use in QGIS represents that it is the most significant open source technology adoption in GIS today.
Mr Pankajakshan.P & Dr. Richard Scaria
Government College Chittur
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