Developing space-time data models and representations for GIS

Simon McBride

“… space by itself and time by itself, are doomed to fade away into mere shadows, and only a kind of union between the two will preserve an independent reality”

(Minkowski 1905 visited in Raper 2000 pg. 98)

Light cones and world lines (from Minkowski 1908)

OVERVIEW

INTRODUCTION MOBILE OBJECTS PROPOSED MOBILE OBJECT MODEL

TIME GEOGRAPHY LINEAR REFERENCING CASE STUDY

PROPOSED SPACE-TIME TOOLBOX CONCLUSIONS & FUTURE DIRECTIONS

INTRODUCTION

Current situation GIS represents a ‘timeless space’ (Raper 2000) Time in GIS is still a problem No fully operational Temporal GIS No commercial Temporal GIS

Why was this the case? The continuous nature of time The cartographic foundations of GIS Existing hardware and software limitations Fragmented research Gap between conceptual models and

implementations

Snapshot-based models• The only commercial model• Many problems that remain unsolved• Only an ad hoc solution using existing spatial structures • Time is captured as slices of reality (time-stamped layers)

Jan. 2000 – Present

Aug. 2000 – Present

Oct. 2000 – Nov. 2000

Nov. 2000 – Present

Road Completion Dates time

Present

Dec. 2000

Sep. 2000

Aug. 2000

Jan. 2000

Object-based models• This model tracks changes in objects through

time instead of locations• Changed information only is stored• Some problems remain unsolved

Jan. 2000 – Present

Aug. 2000 – Present

Oct. 2000 – Nov. 2000

Nov. 2000 – Present

Road Completion Dates time

Present

Nov. 2000

Oct. 2000

Aug. 2000

Jan. 2000

Space-time data model issues

• A broad range of complex issues exist and many challenges remain

• A single data model will NOT solve all the problems

• A ‘holy grail’ data model is impractical • One aspect of temporal GIS will be addressed • A space-time data model for the integration of

mobile objects in GIS is proposed

MOBILE OBJECTS• What are objects?• What are moving objects? • Galton (1995) states that a theory on movement must

includes theories on space, time, objects and position• Changes in mobile objects

• Movement (changes in position)• State (changes in attributes)• Identity ( changes in identity) (Frank 2001)

• Mobile objects interact with their environment• Mobile objects seems to have linear movements

• Important: to store, represent and analyse mobile objects

MOBILE OBJECTS

• Integrating mobile objects in GIS is currently an active research domain

• Some proposals include• A people-oriented GIS (Miller 2002)

• Space-time analysis techniques (Laube and Imfeld 2002)

• Mobile objects within an object-oriented GIS (Bian 2000)

• Space-time data mining techniques for LBS (Smyth 2001) • Space-time model for health data (space-time

clusters) (Mark et al 2001) • Space-time trajectories (Vazirigiannis and Wolfson 2001)

• Abstract Data Types (ADT) (Gueting et al 2003)

PROPOSED MOBILE OBJECT MODEL

• This proposal endeavours to address both space and time in one uniform framework

• Based on time geography, linear referencing and 3D models

• Time geography and linear referencing will be introduced• Time geography models objects in a space-time region (x,y,t)• A basic concept in time geography is the space-time path, which

traces the movement of a object in space-time• Linear referencing can trace the movement of an object over

geographic space from location to location

TIME GEOGRAPHY: Background

• In the 1960’s Hägerstrand developed a paradigm we refer to as time geography

• Time geography focuses on:• The location of activities• The objects who undertake such activities • The space-time region in which such activities take

place• Time geography proposes a geometric

representation of time

TIME GEOGRAPHY: Geometric representation

Path: a representation of a person for a period of time in a defined 2D environmenteg. home, work,

home

spac

e

tim

e

Home Work

TIME GEOGRAPHY: Geometric representation

Station: a representation of a temporal object in a fixed position in spaceeg. opening hours

spac

e

tim

e

location A location B

TIME GEOGRAPHY: Geometric representation

Bundle: formedwhen several space-time paths meet at the same position at the same timeeg. home, restaurant, home

spac

e

tim

e

spac

e

tim

e

t1

t2

Work

TIME GEOGRAPHY: Geometric representation

Prism: a representation of a person’s time budget eg. lunch break

LINEAR REFERENCING

• Linear referencing is another technique for storing, displaying and analysing spatial data

• Linear referencing uses relative position (chainage) along a known feature to store data

• Linear referencing is suited for storing, representing and analysing time geography’s geometric representation of time

LINEAR REFERENCING

PROPOSED MOBILE OBJECT MODEL

• Linear referencing can store a compacted 2D space-time path within a single object

• Mobile objects can be stored in a traditional 2D GIS using linear referencing (id,x,y,m,a(t))

• In 3D GIS: A mobile object is represented by a single space-time path (id,x,y,t,m,a)

• Similar to time geography’s space-time path element

CASE STUDY

• Development environment• ArcGIS™• ArcObjects™• Visual Basic™

• Geographical data (Land Victoria data)• Topographic data • Transportation network data (roads, tracks, etc.)

• Temporal data – mobile objects (Parks Victoria)• Visitors’ movements were monitored using

GPS receivers at Loch Ard Gorge within the Port Campbell National Park

CASE STUDY

PROPOSED SPACE-TIME TOOLBOX

• Query difficulties exist in the temporal dimension• A space-time toolbox has been developed to

analyse and query mobile objects in GIS

• Point instance queries:• Where is object X at time T?

• Interval queries: • Where is object X between T1 and T2?

• Region queries: • Which objects O are located in region R at time T?

Space-time queries

• 3D geometry queries:

• A cube selection would select objects in space-time

• Space-time clusters

• Co-location in time, Co-location in space and Co-location in space and time

Temporal analysis

• 3D GIS is useful for the visualisation of mobile objects (id,x,y,t,m,a) and the background data

• Animation• 3D GIS has a few limitations:

• 3D environment is not a full functional GIS system• Basic queries and selections are available• True 3D topology does not exist at present

CONCLUSIONS & FUTURE DIRECTIONS

• Merging of time geography and linear referencing shows potential in modelling time in GIS

• Minimal data redundancy• Where objects are mobile, all movements are

stored• Some space-time queries were developed

• Develop space-time analysis and queries• Time budgets and space-time pattern analysis

• Build a framework for 3D geometry queries

REFERENCES

• Bian, L. (2000), ‘Object-oriented Representation for Modelling Mobile Objects in an Aquatic Environment’, IJGIS, vol. 14, no. 7, pp. 603 – 623.

• Frank, A.U. (2001). ‘Socio-Economic Units: Their Life and Motion’. In Life and Motion of Socio-Economic Units. eds. Frank, A. U. & Raper, J., London, Taylor and Francis.

• Galton, A. (1995), ‘Towards a Qualitative Theory of Movement’, In Spatial Information Theory, eds. Frank, A. & Kuhn, W., LNCS, pp. 377-396.

• Guting, R., Bohlen, M., Erwig, M., Jensen, C., Lorentzos, N., Nardelli, E., Schneider, M. & Viqueira, J. (2003), ‘Spatio-temporal Models and Languages: An Approach Based on Data Types’, In Spatiotemporal Databases: The Chorochronos Approach., et al. (eds), Springer-Verlag, Berlin.

• Hägerstrand, T. (1970), ‘What about People in Regional Science?’ Papers of Regional Science Association, vol. 24, pp. 7-21.

• Laube, P. & Imfeld, S. (2002), ‘Analyzing Relative Motion within Groups of Trackable Moving Point Objects’, Proceedings of GIScience, eds. Egenhofer, M. J. & Mark, D., Springer-Verlag Berlin-Heidelberg, September 2002, Boulder, CO, USA, pp. 132-144.

REFERENCES• Mark, D., Egenhofer, M., Bian, L. & Rogerson, J. (2001), ‘Spatiotemporal GIS

Analysis for Environmental Health: Solutions using Geospatial Lifelines’, In Geography and Medicine, eds. Flahault. et al., Paris, Elsevier, pp. 65-80.

• Miller, H. (draft), “What about People in Geographic Information Science?”, In Re-Presenting Geographic Information Systems, ed. Unwin, D., John Wiley.

• Minkowski, H. (1908), ‘Space and Time’, Proceedings of the 80th Assembly of German Natural Scientists and Physicians, Köln.

• Raper, J. (2000), ‘Multidimensional Geographic Information Science’, Taylor and Francis, London and New York.

• Smyth, C. (2001), ‘Mining Mobile Trajectories’, In Geographic Data Mining and Knowledge Discovery, eds. Miller, H. J. & Han, J., Taylor and Francis, London, pp. 337 - 361.

• Vazirgiannis, M. & Wolfson, O. (2001), ‘A Spatiotemporal Model and Language for Moving Objects on Road Networks’, In Advances in Spatial and Temporal Databases, ed. Jensen, C., Springer, CA, USA.