Constructing Popular Routes from Uncertain Trajectories
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Constructing Popular Routes from Uncertain Trajectories
Ling-Yin Wei1, Yu Zheng2, Wen-Chih Peng1
1National Chiao Tung University, Taiwan2Microsoft Research Asia, China
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Introduction
• GPS-enabled devices are popular▪ E.g, GPS loggers, smart phones, GPS digital
cameras etc.
• Location-based services are popular▪ Data: check-in records, geo-tagged photos etc.
• Spatial & temporal information
2(40.7488,-73.9898),
11:23 AM
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Uncertain Trajectory (1/3)
• Check-in records
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Geo-locationTime
Uncertain Trajectory
(24.2331,120.89355)
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Uncertain Trajectory (2/3)
• Geo-tagged photos
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Apple Store
Rockefeller Center
Time Square
Grand Central Station
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Uncertain Trajectory (3/3)
• Trails of migratory birds
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Problem Definition
• Data▪ Uncertain trajectories
• User query▪ Some locations & time
constraint
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q1q
2
q3
Top 1 Popular Route
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Application Scenarios
• Trip planning• Advertisement placement• Route recovery
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q1
q2
Using Collective Knowledge
• Possible approach▪ Concatenation
• Ours▪ Mutual reinforcement
learning
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• • •
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• • •
q1
q2
• • •
• • •
• • •
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Framework Overview
• Routable graph construction (off-line)
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Routable Graph
Region: Connected geographical area
Edges in each region
Edges between regions
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Framework Overview
• Routable graph construction (off-line)• Route inference (on-line)
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Routable Graph
Popular Route
q1
q2
q3
Local Route SearchGlobal Route Search
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Region Construction (1/3)
• Space partition▪ Divide a space into non-overlapping cells with
a given cell length
• Trajectory indexing
(1,1)TID PID
Tra3
Tra5
Tra1
1
1
1
(1,2)
(1,3)
(1,4)
(2,1)
(2,2)
(2,3)
(2,4)
(3,1)
(3,2)
(3,3)
(3,4)
(4,1)
(4,2)
(4,3)
(4,4)
GID Density
(1,4) 3
TID Sequence of GIDs
Tra3 (1,4)(1,3)(3,2)(4,1)
Median Density
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Grid Index
Transformed Trajectory
Sorted by median density
l
l Tra1
Tra2
Tra3
Tra4
Tra5
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Region Construction (2/3)
• Region▪ A connected geographical area
• Idea▪ Merge connected cells to form a region
• Observation▪ Tra1 and Tra2 follow the same route but have different
sampled geo-locations
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12p
13p
21p
22p
23p
11p tra1
tra2
Spatially close
tra3
12p
13p
21p
22p
23p
11p
31p
32p
Temporal constraint
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Region Construction (3/3)
• Spatio-temporally correlated relation between trajectories▪ Spatially close
▪ Temporal constraint
•
• Connection support of a cell pair
▪ Minimum connection support C
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Δt1
Δt2
1ip
2jp
2'jp
1'ip
Δt1
Δt22jp
1ip
2'jp
1'ipRule1 Rule2
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Edge Inference
[Edges in a region]Step 1: Let a region be a bidirectional graph firstStep 2: Trajectories + Shortest path based inference
▪ Infer the direction, travel time and support between each two consecutive cells
[Edges between regions]• Build edges between two cells in different regions by
trajectories
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p1 p2
p3
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Route Inference
• Route score (popularity)▪ Given a graph , a route
, the score of the route is
where and
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Local Route Search
• Goal▪ Top K local routes between two consecutive geo-
locations qi, qi+1
• Approach▪ Determine qualified visiting sequences of regions by
travel times▪ A*-like routing algorithm
• where a route
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Sequences of Regions from q1 to q2:
q1
q2
R1
R2
R3
R4
R5
R1→ R2 → R3
R1→ R3
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Global Route Search
• Input▪ Local routes between any two consecutive geo-locations
• Output▪ Top K global routes
• Branch-and-bound search approach▪ E.g., Top 1 global route
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q1
q2
R1
R2
R3
R4
R5
q3
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Route Refinement
• Input▪ Top K global routes: sequences of cells
• Output▪ Top K routes: sequences of segments
• Approach▪ Select GPS track logs for each grid ▪ Adopt linear regression to derive regression lines
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Experiments
• Real dataset▪ Check-in records in Manhattan: 6,600 trajectories▪ GPS track logs in Beijing: 15,000 trajectories
• Effectiveness evaluation▪ Routable graph: correctness of explored connectivity▪ Inferred routes
• Error:▪ T: top K routes (ours)▪ T’: top K trajectories (ground truth)
• Efficiency evaluation▪ Query time
• Competitor▪ MPR [Chen et al., Discovering popular routes from trajectories,
ICDE’11] 19
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Results in Manhattan
• Cell length: 500 m• Minimum connection support: 3• Temporal constraint: 0.2• Time span ∆t: 40 minutes
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Routable Graph Top 1 Popular Route
Union Square Park
New Museum of Contemporary Art
Washington Square Park
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Performance Comparison
• Competitor: MPR [Chen et al., Discovering popular routes from trajectories, ICDE’11]
• Parameters ▪ |q|:2, K:1, cell length: 300 m
• Factors▪ sampling rate S (in minutes), query distance Δd
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Impact of Data Sparseness
• Parameters▪ Cell length: 300 m▪ K:3
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Evaluation of Graph Construction
• Steps of graph construction▪ RG: Region construction▪ RG+: Region construction + Edge inference (Shortest path
based inference)
• Factors▪ minimum connection support C, temporal constraint θ
Con
nect
ivity
Acc
urac
y
Con
nect
ivity
Acc
urac
y
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Effectiveness of Route Refinement
• Parameters▪ Sampling rate S: 5 minutes▪ K:1▪ |q|: 2
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Conclusions
• Developed a route inference framework without the aid of road networks▪ Proposed a routable graph by exploring spatio-temporal
correlations among uncertain trajectories▪ Developed a routing algorithm to construct the top K
popular routes
• Future work▪ Plan routes by considering time-sensitive factors
• Different departure times
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Q & A
Thank You