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Raster Data

Raster Data

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Raster Data

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  1. Raster Data Chapter 7

  2. Introduction • Vector – discrete • Raster – continuous • Continuous • precipitation • elevation • soil erosion • Regular grid cell with value to correspond to the characteristics of the phenomenon

  3. Introduction • Most GIS have both raster and vector • We’ve talked about the data • Data • digital elevation • satellite images • digital orthophotos • scanned maps • graphic files

  4. Elements of Raster Data Model • Grid, raster map, surface cover, or image • Rows and columns with cells • Origin at upper left, 2 dimensional coordinate system • Value = integer or floating point • Usually codes for interpretation • No use for DBMS because grid is both spatial and attribute data

  5. Elements of Raster Data Model • Can have value = “pointer” • Cell size determines resolution • Size vs resolution • Projected on coordinate system • Can be displayed with vector if in same coordinate system • Easier to do data manipulation, aggregation and analysis

  6. Types of Raster Data • Satellite Imagery • remotely sensed • Landsat multispectral, 79 meters, ’72-’92 • Landsat 4, Thematic Mapper, 30 meters, • National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) • French SPOT 1986 • India, Japan

  7. Types of Raster Data • Satellite Imagery • Commercial • Space Imaging 1 meter • Earth Watch Incorporated • Image Processing Packages • ERDAS • ER Mapper • ArcView

  8. Digital Elevation Models • DEM is point based with elevation at center of a cell. • Each file contains • Elevation, • Header: units, min/max elev, proj, accuracy • Four types • 7.5 minute DEM (30 or 10 meter elev, 4 levels) • 30 minute DEM (60 meter) • 1 degree DEM (100 meter) • Alaska DEMs

  9. Digital Elevation Models • Non-USGS DEMS • SPOT • Intermap Technologies (5-10 m x 2-5 m) • Global DEMs • GTOPO30 • ETPOPO5

  10. Digital Orthophotos • Digital Orthophoto Quad • Georeferenced • 3.7 minute DOQQ 1m x 1m • Combines image characteristics of a photograph with the geometric qualities of a map. • Ideal background

  11. Other • Binary scanned files • Digital Raster Graphics (DRG) 8 ft • Graphic • TIFF • GIF • JPEG • GeoTIFF • Proprietary: grids or raster maps

  12. Raster Data Structure, Compression, and Files • Data Structure • Cell-by-cell encoding • Band interleaved (.bil) • Band sequential (.bsq) • Band interleaved by pixel (.bip) • Run-length encoding (.rle • Chain code • Block code • Quadtree

  13. Raster Data Structure, Compression, and Files • Data compression • Algorithms • Lossless or lossy • MrSID • Raster Data Files • Need header information

  14. Projection and Geometric Transformation of Raster Data • Raster must also be geo-referenced. • Transformation techniques similar to vector • Ground control points required • Warping • Resampling • Nearest neighbor • Bilinear interpolation • Cubic convolution

  15. Data Conversion • Rasterization • Vectoriation • Loss?

  16. Integration of Raster and Vector Data • Raster usually background • Many techniques • Draping for 3-D effects