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Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann
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Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Dec 17, 2015

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Page 1: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Context-Aware Similarity of Trajectories

Maike BuchinSomayeh Dodge Bettina Speckmann

Page 2: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Location sampled over time• noisy sampling• geographic context

2:402:50

3:00

3:20 3:30

3:40

3:503:554:10

4:154:20

4:25

4:304:35

Trajectory Data

3:10

Page 3: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Trajectory SimilarityHow similar are two trajectories?

Geographic context needs to be taken into account!

Page 4: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Geographic Context

• Landcover• Network • Terrain • Ambient attributes

Model: labeled polygonal subdivision

Page 5: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Context-Aware Similarity

How does geographic context influence similarity?

Page 6: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Context-Aware Similarity

Geographic context distinguishes trajectories

Page 7: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Context-Aware Similarity

Integrate context & spatial distance: • use time to match points • for matched points add spatial and context distance

(p,t,c)(p‘,t‘,c‘)

for matched points (p,t,c) and (p’,t’,c’) dist(p,p’) + α dist(c,c’)

2. spatial distance(e.g., Euclidean dist)

3. context distance(based on cells)

4. context scale(depends on application)

1. matching based on time (e.g., Fréchet dist)

Ingredients:

Page 8: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Context Distance

Compare two points based on cells they lie in

• Labels• Subdivision distance

Example: dist(p,p’) = dist(sand,grass)

Page 9: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Context Distance

Compare two points based on cells they lie in

• Labels• Subdivision distance

Example: dist(p,p’’) =

dist(sand,sand) = 0 or dist(p,p’’) =

min ( 2*dist(sand,water),

2*dist(sand,grass) )

Page 10: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Computing Similarity

Preprocessing• Compute context distance• Locate trajectory points in

subdivision• Possibly split trajectories

at subdivision boundariesAlgorithm• Adapt known algorithms

using as distance dist(pt,pt’) + α dist(ct,ct’)

2:402:50

3:00

3:20 3:30

3:40

3:503:554:104:15

4:204:25

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C1

C2

C3

Equal time distance: straightforward

Fréchet distance: add context distance per free space cell

Page 11: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Experiments: Hurricane Data

Geographic context• Hurricanes are strongly

influenced by land/sea

Similarity• Prediction• Classification

Page 12: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Experiments: Hurricane Data

Data• Hurricanes

– North Atlantic Basin – years 1995, 2004, 2005– sampled every 6 hours– 48 in total

• Coastline data

Page 13: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Results of Experiments

interesting triple among the 10 most similar hurricane pairs:

• Erin & Katrina become most similar than the other pairs

• order of similarity changes: Rita & Katrina become more similar than Rita & Erin

Rita Katrina Erin2004 2005 1995

Page 14: Context-Aware Similarity of Trajectories Maike Buchin Somayeh Dodge Bettina Speckmann.

Conclusion

We can and should integrate geographic context into the analysis of trajectories!

Future Work:• more data sets• more analysis tasks