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# Raster Data - PowerPoint PPT Presentation

Raster Data. Chapter 7. Introduction. Vector – discrete Raster – continuous Continuous precipitation elevation soil erosion Regular grid cell with value to correspond to the characteristics of the phenomenon. Introduction. Most GIS have both raster and vector

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### Raster Data

Chapter 7

• Vector – discrete

• Raster – continuous

• Continuous

• precipitation

• elevation

• soil erosion

• Regular grid cell with value to correspond to the characteristics of the phenomenon

• Most GIS have both raster and vector

• We’ve talked about the data

• Data

• digital elevation

• satellite images

• digital orthophotos

• scanned maps

• graphic files

• 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

• 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

• 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

• Satellite Imagery

• Commercial

• Space Imaging 1 meter

• Earth Watch Incorporated

• Image Processing Packages

• ERDAS

• ER Mapper

• ArcView

• 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

• Non-USGS DEMS

• SPOT

• Intermap Technologies (5-10 m x 2-5 m)

• Global DEMs

• GTOPO30

• ETPOPO5

• 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

• Binary scanned files

• Digital Raster Graphics (DRG) 8 ft

• Graphic

• TIFF

• GIF

• JPEG

• GeoTIFF

• Proprietary: grids or raster maps

• 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

• Data compression

• Algorithms

• Lossless or lossy

• MrSID

• Raster Data Files

• Need header information

• Raster must also be geo-referenced.

• Transformation techniques similar to vector

• Ground control points required

• Warping

• Resampling

• Nearest neighbor

• Bilinear interpolation

• Cubic convolution

• Rasterization

• Vectoriation

• Loss?

Integration of Raster and Vector Data

• Raster usually background

• Many techniques

• Draping for 3-D effects