Towards a formal classification of generalization operators

1
Towards a formal classification of generalization
operators

• Theodor Foerster
• 4 June 2008, STDIV
• ITC PhD day 2008

2
Overview

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook Conclusion

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Introduction

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

• Generalization
• The adaptation of geo-data according to user and
  use requirements
• Model generalization (? data)
• Cartographic generalization (? maps)
• Generalization process consists of different
  generalization operators

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Generalization operators

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

• Provide an abstract description of generalization
  functionality
• Important to abstract human knowledge
• Allows comparing generalization functionality
• An operator is implemented by different algorithms

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Motivation

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

• Different classifications are available
• Do not cover all aspects
• Project-driven
• Not formal
• Classification is important
• For enabling automated web-based generalization
  processing
• Transparency for evaluation
• Knowledge exchange
• Producing on-the-fly base maps for different
  scenarios on the Web
• RGI 002 DURP ondergronden project
  (www.durpondergronden.nl)

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Gruenreich model

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

Reality
Object generalization
Model generalization
Primary model
Cartographic generalization
Cartographic model
Inspired by Gruenreich (1992), ATKIS - a
topographic information system as a basis for GIS
and digital cartography in Germany
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Classification framework

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

Foerster et al. 2008 A Classification of
Generalization Operators Formalized in OCL.
GI-days 2008.
Operators classified based on their impact
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Model vs. cartographic generalization operators

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

• Model generalization operators can be defined on
  feature type level
• Cartographic generalization operators are defined
  on cartographic feature instance level
• Both are applied on instance level!

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Operator classification

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

• Identified operators are based on literature

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Model generalization operators

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

• Class Selection
• Reclassification
• Collapse
• Combine
• Simplification
• Amalgamation

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Collapse Combine

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

• Changing the geometry type
• Collapse
• Decrease dimensionality
• Combine
• Increase dimensionality
• Goes along with reclassification
• Example Combine leisure sites (modeled as
  points) to touristic attraction (modeled as
  polygon)

Collapse

Combine
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Simplification Amalgamation

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

• Simplification
• Mainly used for data reduction
• Deletes aspects of the feature
• Not that invasive
• Amalgamation
• Amalgamating a group of features to a new feature
  of same geometry type
• Goes along (mostly) with reclassification
• Example Merging adjacent polygons of different
  types of forest to a new feature of type forest.

Simplification

Amalgamation
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Role of symbolization

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

• Exclude symbolization from the cartographic
  generalization process
• Cartographic generalization is always applied on
  symbolized (cartographic) features

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Cartographic generalization operators

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

• Enhancement
• Displacement
• Elimination
• Typification
• Enlargement
• Amalgamation

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Examples cartographic generalization operators

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

Generalization
Generalization
Displacement
Amalgamation
Elimination
Enlargement
Typification
Enhancement
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Outlook

• Introduction motivation
• Classification framework
• Model generalization operators
• Cartographic generalization operators
• Outlook

• Verifying classification by interviews with NMAs
• Harmonizing model generalization and schema
  translation
• Research collaboration with Lassi Lehto _at_ FGI
• Results to be published in an international
  journal
• Extracting implementing a formal description of
  the operators
• Foerster et al (2008) A Classification of
  Generalization Operators Formalized in OCL.
  GI-days 2008.
• Investigating the links between different
  operators

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Conclusion

• Classification framework provides an extensible
  means to classify operators
• Initial classification is based on literature
  research
• Full verification implementation still has to
  be done
• However the classification will always remain
  subjective (up to a certain limit)
• Classification is basis for formalization

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Questions?

• Thank you for your attention!
• For more information
• www.durpondergronden.nl
• Email foerster_at_itc.nl