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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

Raster Data

Chapter 7


Introduction
Introduction

  • Vector – discrete

  • Raster – continuous

  • Continuous

    • precipitation

    • elevation

    • soil erosion

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


Introduction1
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


Elements of raster data model
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


Elements of raster data model1
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


Types of raster data
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


Types of raster data1
Types of Raster Data

  • Satellite Imagery

    • Commercial

    • Space Imaging 1 meter

    • Earth Watch Incorporated

  • Image Processing Packages

    • ERDAS

    • ER Mapper

    • ArcView


Digital elevation models
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


Digital elevation models1
Digital Elevation Models

  • Non-USGS DEMS

    • SPOT

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

  • Global DEMs

    • GTOPO30

    • ETPOPO5


Digital orthophotos
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


Other
Other

  • Binary scanned files

  • Digital Raster Graphics (DRG) 8 ft

  • Graphic

    • TIFF

    • GIF

    • JPEG

    • GeoTIFF

  • Proprietary: grids or raster maps


Raster data structure compression and files
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


Raster data structure compression and files1
Raster Data Structure, Compression, and Files

  • Data compression

    • Algorithms

    • Lossless or lossy

    • MrSID

  • Raster Data Files

    • Need header information


Projection and geometric transformation of raster data
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


Data conversion
Data Conversion

  • Rasterization

  • Vectoriation

  • Loss?


Integration of raster and vector data
Integration of Raster and Vector Data

  • Raster usually background

  • Many techniques

  • Draping for 3-D effects


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