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DTM tasks: generation. Buy global or national data set Collect data. Buy global or national data set. Examples Topographic Data. [Eidenbenz et al, 1997]. (*) completed. DTM tasks: generation. Main steps Data capture Data Sampling Choice of data source Data acquisition techniques

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dtm tasks generation
DTM tasks: generation
  • Buy global or national data set
  • Collect data

Digital Terrain Models by M. Varshosaz

buy global or national data set
Buy global or national data set

Digital Terrain Models by M. Varshosaz

examples topographic data
Examples Topographic Data

[Eidenbenz et al, 1997]

(*) completed

Digital Terrain Models by M. Varshosaz

dtm tasks generation1
DTM tasks: generation
  • Main steps
    • Data capture
      • Data
      • Sampling
      • Choice of data source
      • Data acquisition techniques
    • Model construction
      • Establishment of topological relations
      • Defining a suitable interpolation method
  • Data for a DTM should consist of:
    • Elevation Data:
      • Observations about terrain elevations.
    • Morphological Information:
      • Information about phenomena that significantly influence the shape of the terrain surface (i.e. structural features such as drainage channels, ridges and other surface discontinuities).
  • Key issue:
    • The selection of a particular data acquisition technique for any given application considering the available/required efficiency, cost, and technological maturity.
sampling techniques
Sampling techniques
  • Choice of sampling technique
    • Terrain shape
    • Available instrumentation
    • Required accuracy
  • Techniques:
    • Random/Selective
    • Systematic/grid based
    • Progressive
    • Composite
selective sampling
Selective Sampling
  • Capture topographic break lines.
  • Advantage:
    • Capture all the morphological information associated with the surface.
    • Elevation data are collected whenever needed.
  • Disadvantage:
    • Requires experienced human operator.
    • Automation is very difficult.
random selective sampling
Random/Selective sampling
  • Selection of significant points by the operator
  • Usually results in less points
  • More thought should be given to the structuring and management of the measured data
  • Can not be automated
systematic grid based
Systematic/grid based
  • Systematic pattern of spot heights
  • Can be squares, rectangles, triangles, or hexagonal
  • Sampling patterns are arranged as profiles or regular geometric shapes.
  • Fixed sampling distance is used:
    • Need to determine the optimal sampling interval.
grid sampling discussion
Grid Sampling: Discussion
  • Location of the required grid node is preprogrammed and driven under computer control.
  • Advantage:
    • Can easily be programmed
    • May be applied in a semi-automated or automatic mode.
  • Disadvantages:
    • Too many points are sampled in low relief regions.
    • Too few points are captured in rugged terrain.
progressive sampling procedure
Progressive Sampling: Procedure
  • The sampling process is initiated by measuring a low-density grid.
  • The accuracy of the sampled data is then analysed
    • Wherever necessary, the sampling grid is recursively densified until the required accuracy level is reached.
progressive sampling discussion
Progressive Sampling: Discussion
  • Advantage:
    • Fewer points are needed to accurately represent the DTMs.
  • Disadvantage:
    • Details may still be disregarded in the first run
    • Still more points than necessary
    • Too many points in terrain breaks
    • May fail in areas with sharp discontinuities
composite sampling
Composite Sampling
  • Composite Sampling = Progressive sampling / Systematic sampling + selective sampling:
    • Selective sampling is used to capture abrupt surface changes.
    • Progressive sampling yields the data for the rest of the terrain.
  • Advantage:
    • Recursive refinement of progressive sampling is kept to a minimum and terrain discontinuities are represented accurately.
  • Disadvantage:
    • Requires human intervention (partial automation).
  • Combines grid based and selective techniques
  • Can only partially be automated
data capture
Data capture
  • The choice of data source
    • Size of the area to be modelled
    • Required accuracy
    • Type of the data to be extracted
    • Cost and technological maturity
data capture techniques
Data capture techniques
  • Data capture techniques
    • Ground surveying
    • Photogrammetry
    • Digitising cartographic data sources
    • RADAR, LIDAR (or Laser Scanning), and sonar.