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Building a Visual Summary of Multiple Trajectories - PowerPoint PPT Presentation

Building a Visual Summary of Multiple Trajectories. Natalia Andrienko & Gennady Andrienko http://geoanalytics.net. Introduction. Problem statement.

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Presentation Transcript

Building a Visual Summary of Multiple Trajectories

http://geoanalytics.net

• Given: data about movement of multiple objects {<o, t, x, y>}.o  { o1, o2, …, oN }; t0 ≤ t ≤ tmaxTrajectory: {<o, tk, x, y>} where o = const, tk > tk-1 for k>1

• Example: movement of vehicles and/or pedestrians in a city

• Problem: represent groups of spatially similar trajectories in a summarised form.

• E.g. trajectories with close starts and/or close ends and/or similar routes

• Such groups may be found e.g. by means of clustering

• Purposes:

• Promote abstraction, understanding of common spatial features

• Reduce display clutter and overlapping of symbols

Trajectories on Wednesday morning (6591 trajectories, shown with 20% opacity)

Result of density-based clustering by route similarity (noise excluded)

How can we see several (all) clusters at once? How can we compare the clusters?

A summarised representation (graphical spatial model) of a cluster

Divide the territory using a suitable mesh*

Transform each trajectory into a sequence of moves between areas (cells of the mesh)

Count the moves between pairs of areas

Represent by arrows with varying thickness

* Voronoi polygons built around characteristic points

Groups of trajectories with close ends (or close starts)

47 clusters (noise excluded)

• Numeric estimation of displacement

• Minimization of displacement

• User evaluation

• Application to trajectories stored in a database

• Extending the method to spatio-temporal summarisation