User:Mav/Introduction to GIS notes by maveric149/2002-03-19 Lecture

Introduction to GIS notes by maveric149 2002-03-19 Lecture

Raster data structures

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Cector data structre is good for siaplay discrete features, not. Raster data structure is good fo coverages, generates calure for every cell in a grid.

Examples

  • elevation data, satellite imagery, orthophotes, scanned maps, graphic files

Way use raster?

  • large additonal set of GIS analyses, most GIS software allow simultaneous display a and alysis of reawster and vecotor data.

Componets

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  • Grid consistis of rows and columns
  • Point is difine by a whole cell in raster model
  • line is defined by a sequence of neighboring cells
  • Areas are represented by collections of contiguous cells.

Cells

  • integer vlues represent categorical data
  • floating point numbers typically represtend continuous data
  • No spearation between spatial and attrbute data
  • resolution is determined by cell size. large cells can't represent the precise locacton of spatial features.
  • greid is usually projected on a coordinate system like UTM
  • Grid data have fied cell location

Types of raster data

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remote sensed images (Landsate, AVHRR)

  • SPOT imagery from France
  • all need separtate image processig software (RDAS and ER Mapper)
  • Digital Elevation Models (array of uniformly spaced elevation data that is point based)

Digital orthophot quad

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  • processed aerial photographs to remove distortion caused by camera tilt and relief
  • georeferenced
  • can be registerd with topographic can other maps

Digital raster graphics

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  • scanned USGS topo map

Graphic fies

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TIFF, GIF, and JPEG

Encoding

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  • cell by cell encoding (every cell has a value in the grid) = no compression, used for DEMs
  • Run length encoding (only mention cells that have a specific value & then only note the beginning and end values of each row) = some compression of data
  • Chain code compression (records the boundary of a region of redundant values by specifyin cardinal direction) = greater amount of compression
  • Block code compression (breaks raster region into square blocks) = stars by stating

Compression

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  • Lossless or reversible compression
  • Lossy or Irreversible compression

MrSID (multi-resolution seamless image datbase) allows ecalliung the image at differeent scales and resutions

  • Zip, tar

Distortion

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Warping or rubber sheeting ay be needed to allow the closest fit between raster and vector data (georeferencing)

Conversion

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rasteriation or vectorization of data (both need computer algorihms)

Integration

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allow for processin of sicrete and continuopus data at the same time.