WFM 6202: Remote Sensing and GIS in Water Management

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WFM 6202 Remote Sensing and GIS in Water
Management
Part-B Geographic Information System (GIS)
Lecture-3 Input of Geospatial Data

• Akm Saiful Islam

Institute of Water and Flood Management
(IWFM) Bangladesh University of Engineering and
Technology (BUET)
December, 2006
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Data Acquisition

• As data acquisition or data input of
  geospatial data in digital format is most
  expensive (about 80 of the total GIS project
  cost) and procedures are time consuming in GIS,
  the data sources for data acquisitions should be
  carefully selected for specific purposes.

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Required Data Sources for GIS

• Analog mapsTopographic maps with contours and
  other terrain features and thematic maps with
  respect to defined object classes are digitized
  by digitizers manually or by scanners
  semi-automatically.
• Aerial photographsAnalytical or digital
  photogrammetry is rather expensive but the best
  method for updating
• Satellite imageSatellite images or data are
  available for land use classification, digital
  elevation model (DEM), updating highway network
  etc.
• Ground survey with GPSTotal station together
  with GPS (Global Positioning System) will
  modernize the ground survey.
• Reports and publicationsSocial economic data are
  usually listed in the reports of statistics and
  census with respect to administration units.

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Compare data acquisition methods
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Digitizers for Vector Data Input

• The digitizing operation
• Step 1 affixed a map to a digitizing table.
• Step 2 add control points or tics at four
  corners.
• Step 3 digitize map contents according to the
  map layers
• Step 4 editing errors and clean the dataset
• Step 5 convert from digitizer coordinates to
  map coordinates to store in a spatial database.

Tablet digitizers with a free cursor connected
with a personal computer are the most common
device for digitizing spatial features with the
planimetric coordinates from analog maps.
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Major problems of map digitization

• The map will stretch or shrink day by day which
  makes the newly digitized points slightly off
  from the previous points.
• The map itself has errors.
• Discrepancies across neighboring map sheets will
  produce disconnectivity.

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Selecting a digitizing technique
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Scanners for Raster Data Input

• Scanner are used to convert from analog maps or
  photographs to digital image data in raster
  format.
• Mechanical ScannerIt is called drum scanner
  since a map or an image placed on a drum is
  digitized mechanically with rotation of the drum
  and shift of the sensor. It is accurate but slow.
  
• Video CameraVideo camera with CRT (cathode ray
  tube) is often used to digitize a small part of
  map of firm. This is not very accurate but cheap.
  
• CCD CameraArea CCD camera (called digital still
  camera) instead of video camera will be also
  convenient to acquire digital image data. It is
  more stable and accurate than video camera.
• CCD ScannerFlat bed type or roll feed type
  scanner with linear CCD (charge coupled device)
  is now commonly used to digitize analog maps in
  raster format, either in mono-tone or color mode.
  It is accurate but expensive.

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Major Types of Scanner
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Performance of major scanners
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I/O of scanning process
(a) original document in black (with scanner
resolution in green)
(b) scanned document in gray scale pixel
(0black, 255 white)
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Digital Mapping by Aerial Photogrammetry

• Analytical PhotogrammetryThough computer systems
  are used for aerial triangulation, measuring map
  data, editing and output with pen plotter, a
  stereo pair of analog films are set up in a
  stereo plotter and the operator will manually
  read terrain features through stereo
  photogrammetric plotter called analytical
  plotter.
• Digital PhotogrammetryIn digital photogrammetry,
  aerial films are converted into digital image
  data with high resolution (5-25mm). Digital
  elevation model (DEM) is automatically generated
  with stereo matching using digital
  photogrammetric workstation.

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• Procedures
• of
• Aerial
• Phtogrammetry

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Remote Sensing with Satellite Imagery

• Satellite remote sensing is a modern technology
  to obtain digital image data of the terrain
  surface in the electro-magnetic region of
  visible, infrared and microwave.
• Multi-spectral bands including visible,
  near-infrared and/or thermal infrared are most
  commonly used for production of land use map,
  soil map, geological map, agricultureal map,
  forest map etc. at the scale of 150,000
  250,000.
• A lot of earth observation satellites for
  example landsat, SPOT, ERS-1, JERS-1, IRS,
  Radarsat etc. are available.

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Earth Observation Satellites
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High Resolution Satellites
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Advanced Technologies for Primary Data
Acquisition

• Following advanced technologies will be
  useful for future GIS.
• Electronic Plane Surveying SystemAn integrated
  system of total station with automated tracking
  function, kinematics global positioning system
  (GPS) and a pen computer will replace the
  conventional plane surveying.
• Mobile Mapping SystemDifferent sensors such as
  GPS, INS (inertia navigation system), more than
  two digital cameras, voice recorder etc. are
  fixed on a vehicle in order to map objects in
  close range.
• Laser ScannerAirborne laser scanner together
  with GPS and INS will measure directly the
  terrain releif or DEM with the height accuracy of
  10 cm up to the altitude of 1,000 m.
• SAR InterferometerSAR (synthetic apperture
  radar) inter-ferometry is a new technology to
  produce DEM automatically by special
  interferometric processing of a pair of SAR
  images.

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Advanced Technologies
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Advanced Technologies (contd..)
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Rasterization

• Conversion between raster and vector data is
  very useful in practical applications of GIS.
• Rasterization refers to conversion from vector to
  raster data.
• Raster format is more convennient to produce
  color coded polygon maps such as color coded land
  use map, while map digitizing in vector format is
  more easier to trace only the boundary.
• Rasterization is also useful to integrate GIS
  with remote sensing becaues remote sensing images
  are in raster format.

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Conversion Vector to Raster

• trapezoid area can be applied to convert
  vectorized polygon to rasterized polygon with
  grid cells

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Vectorization

• Vectorization refers to conversion from raster
  to vector data, which is often called raster
  vector conversion.

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Raster Vector Conversion

• Schematic of the raster vector conversion by
  which left and right polygons are identified