1. Developing space-time data models and representations for GIS
Simon McBride

2. “… 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)

3. OVERVIEW INTRODUCTION MOBILE OBJECTS PROPOSED MOBILE OBJECT MODEL
TIME GEOGRAPHY
LINEAR REFERENCING
CASE STUDY
PROPOSED SPACE-TIME TOOLBOX
CONCLUSIONS & FUTURE DIRECTIONS

4. INTRODUCTION Current situation Why was this the case?
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

5. 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 – Present
Aug – Present
Oct – Nov. 2000
Nov – Present
Road Completion Dates
time
Present
Dec. 2000
Sep. 2000
Aug. 2000
Jan. 2000

6. Object-based models
This model tracks changes in objects through time instead of locations
Changed information only is stored
Some problems remain unsolved
Jan – Present
Aug – Present
Oct – Nov. 2000
Nov – Present
Road Completion Dates
time
Present
Nov. 2000
Oct. 2000
Aug. 2000
Jan. 2000

7. 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

8. 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

9. 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)

10. 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

11. 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

12. TIME GEOGRAPHY: Geometric representation
Path: a
representation of a
person for a period of
time in a defined 2D
environment
eg. home, work,
home
space
time
Home
Work

13. TIME GEOGRAPHY: Geometric representation
Station: a
representation of
a temporal object in a
fixed position in
space
eg. opening hours
space
time
location A
location B

14. TIME GEOGRAPHY: Geometric representation
Bundle: formed
when several space-
time paths meet at
the same position at
the same time
eg. home,
restaurant, home
space
time

15. TIME GEOGRAPHY: Geometric representation
Prism: a
representation of
a person’s time
budget
eg. lunch break
space
time t1 t2
Work

16. 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

17. LINEAR REFERENCING

18. 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

19. 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

20. CASE STUDY

21. 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?

22. 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

23. 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

24. 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

25. 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
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
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

26. 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
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
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.