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, Thematic MapperThematic Mapper –National Oceanic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) AVHRR –French SPOT 1986 SPOT –India, Japan IndiaJapanIndiaJapan

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

8. Digital Elevation Models  DEM is point based with elevation at center of a cell. DEM  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) Intermap TechnologiesIntermap Technologies  Global DEMs –GTOPO30 GTOPO30 –ETPOPO5 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