Raster data model

Raster data model - GIS

1. RASTER DATA MODEL A SEMINOR ON

2. SEMINOR CONTENTS INTRODUCTION RASTER DATA MODEL USES OF RASTER DATA MODEL TYPES OF RASTER DATA VECTOR GRAPHICS RASTER DATA FORMATS ADVANTAGES AND DISADVANTAGES CONCLUSION REFERENCE

3. INTRODUTION G IS (Geographic Information System) is an integrated system of computer Hardware and Software coupled with procedures and human analyst which together support the capture, management, manipulation, analysis, modelling and display of spatially referenced data.

4. Cont… HARD WARE Computers, Networks, Printers SOFTWARE GIS Software, Database software, OS Software, Network Software DATA Vector Data, Raster Data , Image Data, Attribute Data METHODS Guidelines, Standards, Procedures PEOPLES Administrators, Managers, GIS Technician's, Application experts , End User, Consumers

5. Types of GIS Data The basic data type in a GIS reflects traditional data found on a map. Accordingly, GIS technology utilizes two basic types of data : SPATIAL DATA Describes the absolute and relative location of geographic features . ATTRIBUTE DATA Describes characteristics of the spatial features. These characteristics can be quantitative and/or qualitative in nature.

6. GIS data represents real objects which can be stored under two broad types known as Vector Data and Raster Data VECTOR DATA The vector data is made up of points, lines and polygons. They are x,y,z data points . Data Representation

7. Raster data model The Raster D ata is made up of a matrix of grids. The grids may be occupied by pixels (cells ). In its simplest form, a raster consists of a matrix of cells(or pixels) organized into Rows and C olumns (or a grid ) Where each cell contains a value representing information such as temperature. Raster’s are digital Aerial photographs, imagery from satellites, digital pictures, or even scanned maps.

8. Cells are identified by their positions in the grid . Raster data is geo-referenced by: Real world coordinates of the reference point Cell size in real world distance Use the upper-left or lower-left corner of grid as the reference point .

9. As compared to the vector data structure, the raster data structure is not particularly accurate at representing discrete features - that is, those features that have a distinct boundary or shape. The term Raster implies a regularly spaced grid. Raster data consists of rows and columns of cells (or pixels). In this format a single value is stored against each cell. Raster data can represent a multiplicity of things including : DIFFERENCE BETWEEN RASTER AND VECTOR DATA SETS Cont…

10. Kind of the image Size and scale Resolution/compression Image Format in which it is represented Image files may be drawing files, shape files, header files, image files and sizes Vector graphics ( X,Y,Z, lines , arcs, color filled zones) Raster graphics ( pixels – grid pattern, each pixel has a color) Ranges of colors as per R,G,B Total colors 256 x 256 x 256 TWO TYPES OF GRAPHICS CHARACTERISTICS OF DIGITAL IMAGES

11. Red, Green, Blue 250, 0,0 0,0,0 0,0,250 COMPONENTS OF COLOR

12. Raster data is stored in various formats; some of these include BMP ( Bitmap Image) TIFF (Tag Index File Format) JPEG/JPG   (Joint Photographic Expert Group) IMG (Image File Format) GIF ( Graphic Intercharge Format) PSP ( Portable Sony Play station) CDR ( Crash Data Retrieval) POPULAR RASTER IMAGE FILES

13. Vector (also known as "object-oriented") graphics are constructed using mathematical formulas describing shapes, colors, and placement. Rather than a grid of pixels, a vector graphic consists of shapes, curves, lines, and text which together make a picture. Vector graphics are resolution-independent--that is, they can be scaled to any size and printed at  any resolution without losing detail or clarity. As a result, vector graphics are the best choice for representing bold graphics that must retain crisp lines when scaled to various sizes--for example, logos. VECTOR GRAPHICS

14. VECTOR MAGNIFICATION without losing detail or clarity

15. I s a language for describing vector graphics in XML (Extensible Markup Language) . With SVG , one can code graphics directly into an XML document. Example of a Gray-scale Bit-map Image Each pixel is usually stored as a byte (value between 0 to 255) A 640 x 480 Gray-scale image requires over 300 KB of storage. SVG, OR SCALABLE VECTOR GRAPHICS GRAY-SCALE

16. One byte for each pixel Supports 256 out of the millions possible, acceptable colour quality Requires Colour Look-Up Tables (LUTs) A 640 x 480 8-bit colour image requires 307.2 KB of storage (the same as 8-bit gray-scale) 8-BIT IMAGES

17. 24-bit image Each pixel is represented by three bytes (e.g., RGB) Supports 256 x 256 x 256 possible combined colours ( 16,777,216) A 640 x 480 24-bit colour image would require 921.6 KB of storage

18. A BITMAP ENLARGEMENT

19. Image graphics in Medical diagnostics

20. Imaging systems in hospitals

21. Photographic images-digital

22. VECTOR GRAPHICS - CLIP ART

23. Raster Graphics

24. Depends on the Image Resolution Image Size, number of pixels Compression and decompression Display systems Main factor: Pixel dimension The display size of an image on-screen is determined by the pixel dimensions of the image plus the size and setting of the monitor. QUALITY OF AN IMAGE

25. Example of an image displayed on monitors of various sizes and resolutions

26. PIXELS PER SQ. INCH EXAMPLE OF AN IMAGE AT 72-PPI AND 300-PPI (  Pixels Per Inch  )

27. Image resolution Monitor resolution/ Printer resolution Screen frequency File type, format, compression File size Maximum pixel Key factors

28. A Raster data model is variously called a grid. A Grid consists of Rows , Columns , and cells. The origin of rows and columns is at a upper left corner of the grid. Rows function as a Y co-ordinates and columns' as X co-ordinates in a two dimensional co-ordinate system. A cell is defined by its location in terms of rows and columns. ELEMENTS IN RASTER DATA MODEL

29. A raster cell stores a single value, however this can be extended by using raster bands. An example of this is the use of bands to represent RGB colours, colour maps , or an extended attribute table with one row for each unique cell value . Raster model divides the area into grid cells or pixel. Each grid cell is filled with the measured attribute values. It can represent points, lines and area Resolution depends on real world area represented by each grid cell. cont …

30. Discrete and Continuons Data When data is presented in raster format, they may be discrete or continuous data . 1. The numeric distribution of discrete data are independent numbers and the geographic distribution has abrupt boundaries . 2. The numeric distribution of continuous data are a range of values and their geographic distribution is along a spatial gradient.

31. Geographical variation in the real world is infinitely complex The closer you look, the more detail you see, almost without limit It would take an infinitely large database to capture the real world precisely. Raster grid cells allow us to approximate the variation over a landscape. Data must somehow be reduced to a finite and manageable quantity by a process of generalization or abstraction. We have to pick out the most characteristic features. Geographical variation must be represented in terms of discrete elements or objects USES OF RASTER DATA MODEL

32. TYPES OF RASTER DATA SATELLITE IMAGERY Remotely sensed satellite data are recorded in raster format. The pixel value in a satellite image represents light energy reflected or emitted from the Earth’s surface. Land use, land cover and hydrography can be classified from image processing system. Satellite images can be displayed in black and white or in colour. This Half-meter Resolution Image Of Khalifa Sports City Complex Qatar, Was Collected By The Geoeye-1 Satellite On January 10, 2009

33. DEM consists of an array of uniformly spaced elevation data. DEM are produced from: A stereo-plotter and aerial photograph with overlapping areas. Satellite imagery such as SPOT stereo model using special software . DIGITAL ELEVATION MODELS (DEM)

34. Prepared from aerial photograph or other remotely sensed data. They are geo-referenced and can be registered with topographic and other maps. DIGITAL ORTHOPHOTOS

35. BINARY SCANNED FILES Scanned image containing values of 1 and 0. Maps to be digitized are typically scanned at 300 or 400 dpi (dots per square inch). GRAPHIC FILES Maps , photographs and images can be stored as digital graphic files.

36. The Geographic location of each cell is implied by its position in the cell matrix. Due to the nature of the data storage technique, data analysis is usually easy to program and quick to perform . The inherent nature of raster maps, e.g. one attribute maps, is ideally suited for mathematical modelling and quantitative analysis. Discrete data, e.g . forestry stands, is accommodated equally well as continuous data, e.g. Elevation data, and facilitates the integrating of the two data types. Grid-cell systems are very compatible with raster-based output devices. ADVANTAGES cont …

37. The cell size determines the resolution at which the data is represented; It is especially difficult to adequately represent linear features depending on the cell resolution. Since most input data is in vector form, data must undergo vector-to-raster conversion. Besides increased processing requirements this may introduce data integrity concerns due to generalization and choice of inappropriate cell size. Most output maps from grid-cell systems do not conform to high-quality cartographic needs. DISADVANTAGES

38. CONCLUSION GIS data is stored in two types: Raster Data and Vector Data Raster data consists of rows and columns of cells (or pixels). Raster data may be discrete or continuous. Raster data allows approximation of variation over a landscape. It makes data finite and manageable . Types of raster includes satellite imageries, Digital Elevation Models, Digital Orthophotos, binary scanned files and graphic files. Raster data may be stored as TIFF, Geo TIFF , GIF, JPEG, etc. The inherent nature of raster maps, e.g. one attribute maps, is ideally suited for mathematical modelling and quantitative analysis.

39. REFERENCE B. BHATTA , (2008) Remote Sensing And Gis Oxford University Press, Pp : 442,121,129,135, 144. FLOYD F. SABINS , (1996/1997) Remote Sensing Principles And Interpretation , W.H. FREEMAN AND COMPANY NEWYORK 3 rd Edition, Pp : 29,69,105,177,236. KALICHARAN SAHU , (2008), Text Book Of Remote Sensing And Gis , Atlantic Publications, Pp : 1-2,127-198. Textbook Of Remote Sensing And Geographical Information System , M.ANJI REDDY , Second Edition, Pp 1-23. http://en.wikipedia.org/wiki/Raster_data http://geospatial.referata.com/wiki/Raster_Data_Model http://gis.stackexchange.com/questions/57142/what-is-the-difference-between-vector-and-raster-data-models WEBSITES BOOKS

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