Data Processing Systems Babu Ram Dawadi

Introduction Data processing systems are computer systems with appropriate hardware components for the processing, storage and transfer of data, as well as software components for the management of the hardware, peripheral devices and data

Hardware and software trends The developments in computer hardware proceed at an enormously fast speed Computer gets smaller and at the same time, their performance increases Computers have become increasingly portable Hand-held computers are now commonplace in business and personal use. Portable computers will soon become common and cheap allowing field surveyors, for instance, to take with them powerful computers into the field, possibly hooked up with GPS receivers for instantaneous georeferencing

Digitizers (Tablets), Plotters and Scanners Digitizing Tablet is a common device for drawing, painting, or interactively selecting coordinate positions on an object A digitizing tablet consists of an electronic tablet and a cursor or pen (stylus). The tablet contains electronics that enable it to detect movement of the cursor

GIS software The main characteristics of a GIS software package are its analytical functions that provide means for deriving new geo-information from existing spatial and attribute data A GIS can be again defined as a computer based system that provides the following four sets of capabilities to handle geo-referenced data. Input Data management (storage and retrieval) Manipulation and analysis, and Output

All GIS packages available on the market have their strengths and weaknesses, resulting typically from the package’s development history and/or intended application domain(s) Some GIS have traditionally focused more on support for raster manipulation, others more on (vector based) spatial objects

Software architecture and functionality of GIS GIS always consists of modules for input, storage analysis, display and output of spatial data Database Data Input Query and Analysis Output and Visualization Functional Components of GIS

Data input Method Devices Manual digitizing coordinate entry via keyboard Digitizing tablet with cursor Mouse cursor on the computer monitor (digital) Photogrammetry Automatic digitizing Scanner Semi-Automatic digitizing Line following devices Input of available digital data Magnetic tape or CD-ROM Via computer network

Data output and visualization Method Devices Hard copy Printer Plotter Film writer Soft copy Computer screen (CRT), flat panel Output of digital data sets Magnetic tape CD-ROM computer network

Data storage In most of the available processing systems, data are organized in layers according to different themes or scales They are stored either according to thematic categories, like land use, topography and administrative subdivisions, or according to map scales representing map series of different scale

Querying, maintenance and spatial analysis The most distinguishing part of a GIS is its functions for spatial analysis The following three classes are the most important query and analysis functions of a GIS, Maintenance and analysis of spatial data, Maintenance and analysis of attribute data, and Integrated analysis of spatial data and attribute data. The first and third are GIS specific.

Maintenance and analysis of spatial data Maintenance of spatial data can be best defined as the combined activities to keep the data set up-to-date and as supportive as possible to the user community Format transformation function convert between data formats of different systems Geographic transformations help to obtain data from an original hardcopy source through digitizing the correct world geometry Map projections provide means to map geographic coordinates onto a flat surface (for map production), and vice versa

Edge matching is the process of joining two or more map sheets Edge matching is the process of joining two or more map sheets. At the map sheet edges, feature representations have to be matched so as to be combined Graphic element editing allows changing digitized features so as to correct errors, and to prepare a clean data set for topology building. Coordinate thinning is a process that often is applied to remove redundant vertices from line representations.

Integrated analysis of spatial data and attribute data Retrieval, classification and measurement functions Retrieval functions allow the selective search and manipulation of data without the need to create new entities. Classification allows assigning features to a class on the basis of attribute values or attribute ranges. Generalization is a function that joins different classes of objects with common characteristics to a higher label class. Management functions allow measuring distances, lengths or areas.

Overlay functions belong to the most frequently used functions in a GIS application They allow combining two spatial data layers by applying the set theory operations of intersection, union, difference and complement using set of positions as their arguments the potato fields on clay soils (intersection), the fields where potato or maize is the crop (union), the potato fields not on clay soils (difference), the fields that do not have potato as crop (complement)

Neighborhood functions operate on neighbouring features of a given set of features. Search functions allow the retrieval of features that fall within a given search window (which may be rectangle, circle or polygon). Line-in-polygon and point-in-polygon functions determine whether a given linear or point feature is located within a given polygon, or they report the polygons that a given point or line are contained in. Proximity function is the buffer zone generation. This function determines a fixed-width environment surrounding a given feature. Interpolation functions predict unknown values using the known values at nearby locations.

Connection functions accumulate values as they traverse over a feature or over a set of features. Network analysis is used to compute the shortest path (in terms of distance or travel time) between two points in a network. Visibility functions are used to compute the points that are visible from a given location