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DOI: 10.4230/LIPIcs.SoCG.2025.34

Simplification of Trajectory Streams

Authors: Siu-Wing Cheng, Haoqiang Huang, and Le Jiang

Published in: LIPIcs, Volume 332, 41st International Symposium on Computational Geometry (SoCG 2025)

Abstract

While there are software systems that simplify trajectory streams on the fly, few curve simplification algorithms with quality guarantees fit the streaming requirements. We present streaming algorithms for two such problems under the Fréchet distance d_F in ℝ^d for some constant d ≥ 2. Consider a polygonal curve τ in ℝ^d in a stream. We present a streaming algorithm that, for any ε ∈ (0,1) and δ > 0, produces a curve σ such that d_F(σ,τ[v₁,v_i]) ≤ (1+ε)δ and |σ| ≤ 2 opt-2, where τ[v₁,v_i] is the prefix in the stream so far, and opt = min{|σ'|: d_F(σ',τ[v₁,v_i]) ≤ δ}. Let α = 2(d-1)⌊d/2⌋² + d. The working storage is O(ε^{-α}). Each vertex is processed in O(ε^{-α} log 1/ε) time for d ∈ {2,3} and O(ε^{-α}) time for d ≥ 4 . Thus, the whole τ can be simplified in O(ε^{-α}|τ| log 1/ε) time. Ignoring polynomial factors in 1/ε, this running time is a factor |τ| faster than the best static algorithm that offers the same guarantees. We present another streaming algorithm that, for any integer k ≥ 2 and any ε ∈ (0,1/17), maintains a curve σ such that |σ| ≤ 2k-2 and d_F(σ,τ[v₁,v_i]) ≤ (1+ε) ⋅ min{d_F(σ',τ[v₁,v_i]): |σ'| ≤ k}, where τ[v₁,v_i] is the prefix in the stream so far. The working storage is O((kε^{-1}+ε^{-(α+1)})log 1/(ε)). Each vertex is processed in O(kε^{-(α+1)}log²1/(ε)) time for d ∈ {2,3} and O(kε^{-(α+1)} log 1/ε) time for d ≥ 4.

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Siu-Wing Cheng, Haoqiang Huang, and Le Jiang. Simplification of Trajectory Streams. In 41st International Symposium on Computational Geometry (SoCG 2025). Leibniz International Proceedings in Informatics (LIPIcs), Volume 332, pp. 34:1-34:14, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2025)

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@InProceedings{cheng_et_al:LIPIcs.SoCG.2025.34,
  author =	{Cheng, Siu-Wing and Huang, Haoqiang and Jiang, Le},
  title =	{{Simplification of Trajectory Streams}},
  booktitle =	{41st International Symposium on Computational Geometry (SoCG 2025)},
  pages =	{34:1--34:14},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-370-6},
  ISSN =	{1868-8969},
  year =	{2025},
  volume =	{332},
  editor =	{Aichholzer, Oswin and Wang, Haitao},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.SoCG.2025.34},
  URN =		{urn:nbn:de:0030-drops-231860},
  doi =		{10.4230/LIPIcs.SoCG.2025.34},
  annote =	{Keywords: streaming algorithm, curve simplification, Fr\'{e}chet distance}
}

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Track A: Algorithms, Complexity and Games

DOI: 10.4230/LIPIcs.ICALP.2023.40

Approximate Nearest Neighbor for Polygonal Curves Under Fréchet Distance

Authors: Siu-Wing Cheng and Haoqiang Huang

Published in: LIPIcs, Volume 261, 50th International Colloquium on Automata, Languages, and Programming (ICALP 2023)

Abstract

We propose κ-approximate nearest neighbor (ANN) data structures for n polygonal curves under the Fréchet distance in ℝ^d, where κ ∈ {1+ε,3+ε} and d ≥ 2. We assume that every input curve has at most m vertices, every query curve has at most k vertices, k ≪ m, and k is given for preprocessing. The query times are Õ(k(mn)^{0.5+ε}/ε^d+ k(d/ε)^O(dk)) for (1+ε)-ANN and Õ(k(mn)^{0.5+ε}/ε^d) for (3+ε)-ANN. The space and expected preprocessing time are Õ(k(mnd^d/ε^d)^O(k+1/ε²)) in both cases. In two and three dimensions, we improve the query times to O(1/ε)^O(k) ⋅ Õ(k) for (1+ε)-ANN and Õ(k) for (3+ε)-ANN. The space and expected preprocessing time improve to O(mn/ε)^O(k) ⋅ Õ(k) in both cases. For ease of presentation, we treat factors in our bounds that depend purely on d as O(1). The hidden polylog factors in the big-Õ notation have powers dependent on d.

Cite as

Siu-Wing Cheng and Haoqiang Huang. Approximate Nearest Neighbor for Polygonal Curves Under Fréchet Distance. In 50th International Colloquium on Automata, Languages, and Programming (ICALP 2023). Leibniz International Proceedings in Informatics (LIPIcs), Volume 261, pp. 40:1-40:18, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2023)

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@InProceedings{cheng_et_al:LIPIcs.ICALP.2023.40,
  author =	{Cheng, Siu-Wing and Huang, Haoqiang},
  title =	{{Approximate Nearest Neighbor for Polygonal Curves Under Fr\'{e}chet Distance}},
  booktitle =	{50th International Colloquium on Automata, Languages, and Programming (ICALP 2023)},
  pages =	{40:1--40:18},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-278-5},
  ISSN =	{1868-8969},
  year =	{2023},
  volume =	{261},
  editor =	{Etessami, Kousha and Feige, Uriel and Puppis, Gabriele},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ICALP.2023.40},
  URN =		{urn:nbn:de:0030-drops-180929},
  doi =		{10.4230/LIPIcs.ICALP.2023.40},
  annote =	{Keywords: Polygonal curves, Fr\'{e}chet distance, approximate nearest neighbor}
}

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Documents authored by Huang, Haoqiang

Simplification of Trajectory Streams

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Approximate Nearest Neighbor for Polygonal Curves Under Fréchet Distance

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