Spatial Data acquisition

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Spatial data acquisition
Jwan M. ALDOSKI Geospatial Information Science
Research Center (GISRC), Faculty of Engineering,
Universiti Putra Malaysia, 43400 UPM Serdang,
Selangor Darul Ehsan. Malaysia.
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Spatial data acquisition

• There are two methods for spatial data
  acquisition
• Primary methods Surveying, Photogrammetry,
  GNSS and Remote Sensing
• Secondary methods
• Digitization, Automatic line following, and
  scanning

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Surveying

• Surveying is a technique of mapping features
  using different instruments.
• Equipments include tape (short distance), level
  (height), theodolite/total station (angle,
  distance)

Digital level
Total station
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Photogrammetry

• Photogrammetry is a technique of mapping features
  using aerial photos
• Photos (Black/white/color/infrared) are taken by
  a set of cameras onboard an airplane.
• Instruments that can be used to help in the
  interpretation are stereoscope, stereo plotters
  (deriving contours and Digital Elevation Model
  DEM)

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Example of aerial photo Kuala Lumpur
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Global Navigation Satellite Systems (GNSS)

• GNSS are sets of satellites that send signal
  which is received by users to determine (X,Y,Z)
  of any point on the earth
• Receivers vary in accuracy, size, and cost (e.g.
  Trimble, Leica, Magellan, Garmin and Javad)
• GPS, GLONASS, Galileo, QZSS, IRNSS, Beidou

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Remote Sensing

• Remote sensing is a technique of mapping features
  using Satellite imagery. Images (Black/white or
  color-Multiple bands) are taken by a set of
  sensors onboard a satellite
• Features are mapped from satellite imagery using
  visual interpretation or automatic classification
• Example of remote sensing satellites are LANDSAT,
  ERS-1,2, SPOT, JERS-1, RADARSAT

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Space technology elements
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The secondary data acquisition

• Designed to transfer data into the GIS from
  secondary sources (image, reports, attribute and
  map data)
• Must be provided with means for spatial
  referencing
• Keyboard entry is a good example of secondary
  data input
• Input through keyboard is time consuming, but it
  can be more accurate. It is suitable for small
  areas i.e. when the number of points/lines/areas
  are limited
• Two other common ways are digitizing and scanning

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Digitizing and scanning

• Digitization is a process of converting existing
  maps to digital form (vector format)
• When cross hair is moved over the screen its
  location is known because the georeferencing of
  map/images senses it location.
• Scanning is a process of converting existing maps
  to digital form (raster format)
• A scanner is connected to a computer and map
  features are scanned automatically
• Scanners are available at different sizes (A4
  till A0) and different accuracy (600 dpi, 1000
  dpi etc)

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Rasterization and vectorization

• Regardless of input device, it is necessary to
  determine if the final product will be raster or
  vector
• Most GIS programs allow conversion between the
  two, but problems are involved
• If vector to raster, cell size is also important,
  but the results are satisfactory
• If raster to vector, lines become blocky and
  step-like, cant reverse the procedure to produce
  original content of vector line also, resolution
  (or cell size) has a direct effect on the spatial
  integrity of the object
• Several algorithms can be applied as smoothing
  function to vector lines

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Thank you