raster data model

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  • charCharacter or small integer.1bytesigned: -128 to 127unsigned: 0 to 255short int (short)Short Integer.2bytessigned: -32768 to 32767unsigned: 0 to 65535intInteger.4bytessigned: -2147483648 to 2147483647unsigned: 0 to 4294967295long int (long)Long integer.4bytessigned: -2147483648 to 2147483647unsigned: 0 to 4294967295
  • raster data model

    1. 1. Raster Data Model
    2. 2. GIS data models Model Abstraction of realworld/process/phenomenon GIS data model Set of constructs/rules for describing or representing the real world within a computer Two data models Vector Raster
    3. 3. Data Models Raster A cellular based data structure composed of rows and columns for storing images. Homogenous units are called cells or pixels. • Mainly Used for representing continuous surface e.g. reflectivity of EMR, elevation, rainfall, soil/landuse etc., Vector A coordinate based data structure commonly used to represent geographic features. Homogenous units are points, lines, and polygons. • Mostly used for representing discrete geographical features such as building, wells, roads etc.,
    4. 4. A grid defines geographic space as a matrix of identically-sized square cells. Each cell holds a numeric value that measures a geographic attribute (like elevation) for that unit of space. Source: http://www.ce.utexas.edu/prof/maidment/class.html
    5. 5. Grid data structure Grid size is defined by extent, spacing and no data value information Number of rows, number of column Cell sizes (X and Y) Top, left , bottom and right coordinates Source: http://www.ce.utexas.edu/prof/maidment/class.html
    6. 6. Definition of a Grid Cell size Number of rows NODATA cell (X,Y) Number of Columns Source: http://www.ce.utexas.edu/prof/maidment/class.html
    7. 7. Somewhere on earth
    8. 8. Raster grid is placed
    9. 9. Reality >>> Raster value The average EMR is measured within each grid Depending on the average intensity of the EMR a numeric value is assigned for each grid
    10. 10. Spatial resolution finer Coarser
    11. 11. Spatial Resolution Examples 15 meters 60 meters 30 meters Source: G. Bryan Bailey, U.S.Geological Survey, EROS Data Center, gbbailey@usgs.gov
    12. 12. NODATA Cells
    13. 13. Types of Raster Based on the data type Integer • Binary or Boolean (0 or 1) • Grayscale (Signed/Un-signed, 8 bit, 16bit, 32bit) Real (floating decimal point) • Grayscale (32 bit, 64 bit) Based on the number of bands Single band Multi-band  Remotely sensed data
    14. 14. red green blue UV 0.4 0.5 0.6 0.7 Near-infrared
    15. 15. Raster Calculator Cell by cell evaluation of mathematical functions
    16. 16. Example 7 5 6 6 2 3 4 3 = 5 2 2 3 Precipitation Losses (Evaporation, Infiltration) = Runoff
    17. 17. Raster Data Formats TIFF – GeoTIFF Tagged Image File Format GIF Graphic Interchange Format BMP BitMap format JPEG Joint Photographic Experts Group
    18. 18. Other Formats ArcInfo GRID ERDAS Imagine ASCII Binary format Band sequential Band Interleaved by Line Band Interleaved by Pixel
    19. 19. Raster Vs Vector
    20. 20. Advantages Disadvantages
    21. 21. Data Raster Grid cell or pixel
    22. 22. Data
    23. 23. Data Vector
    24. 24. Data Vector Raster
    25. 25. Data Conversion Integrate other GIS data with Remote Sensing Rasterization Vector to Raster Can only approximate original location • Pixel resolution Vectorization Raster to Vector
    26. 26. Raster Generalization: case 1 Largest share rule Central point rule
    27. 27. Raster Generalization: Case 2 Largest share rule Central point rule
    28. 28. Vectorization Raster to vector More complex • Points • Lines • Polygons Edge enhancement Classification Vectorizing Topology need to be built

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