DTM tasks: generation
description
Transcript of DTM tasks: generation
Digital Terrain Models by M. Varshosaz 1
DTM tasks: generation Buy global or national data set Collect data
Digital Terrain Models by M. Varshosaz 2
Buy global or national data set
Digital Terrain Models by M. Varshosaz 3
Examples Topographic Data
(*) completed[Eidenbenz et al, 1997]
Examples: 3 ENMAs
Current products Production method
Current activity
OS (GB)
Paper maps 1:1250, 1:2500 2D database ( 1:1250 , 1:2500 ) National DTM ( 1:10k,1:50k) Road centreline DB
Photogrammetry Map digitizing (*) Map digitizing (*)
DB updating by A.Ph. & monoplot. Contours updating by A.Photogr.
IGN (F)
Paper maps 1:25,50,100,250 k 2D database (acc. 10m) 2.5D database (acc. 2m) National DTM Road DB
Map digitizing (*) Photogrammetry Map digitizing (*)
Data collection by A.Ph. & D.Ph. Develop prod. line for image matching Develop prod.line for auto road extrac.
SFOT (CH)
Paper maps 25, 50, 100k 2D database (acc. 5m) ( 1:25k) National DTM ( 1:25,000 )
Photogr. (*) Map digitizing (*) Map digitizing (*)
Map revision Prepare for upgrading to 2.5D Develop prod. line for auto AT Develop prod. line for digital OP from auto AT and national DTM
NCC Paper maps (1/10,000 , 1/25,000 ) DTM of some states (1/25,000 )
Photogrammetry Production/Revision
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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
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Data 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.
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Sampling techniques Choice of sampling technique
Terrain shape Available instrumentation Required accuracy
Techniques: Random/Selective Systematic/grid based Progressive Composite
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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.
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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
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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.
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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.
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Progressive Sampling: Procedure The sampling process is initiated by measuring
a low-density grid. The accuracy of the sampled data is then
analysedWherever necessary, the sampling grid is
recursively densified until the required accuracy level is reached.
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Progressive Sampling: DiscussionAdvantage:
Fewer points are needed to accurately represent the DTMs.
Disadvantage:Details may still be disregarded in the first runStill more points than necessaryToo many points in terrain breaksMay fail in areas with sharp discontinuities
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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).
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Composite Combines grid based and selective
techniques Can only partially be automated
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Sampling Methods: Summary
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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
Ground surveyingPhotogrammetryDigitising cartographic data sourcesRADAR, LIDAR (or Laser Scanning), and sonar.
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Choice of Data Acquisition Techniques