A rotation invariant filter for two-dimensional string matching

  • Kimmo Fredriksson
  • Esko Ukkonen
Session III
Part of the Lecture Notes in Computer Science book series (LNCS, volume 1448)


We consider the problem of finding the occurrences of two-dimensional pattern P[1..m, 1..m] in two-dimensional text T[1..n, 1..n] when also rotations of P are allowed. A fast filtration-type algorithm is developed that finds in T the locations where a rotated P can occur. The, corresponding rotations are also found. The algorithm first reads from P a linear string of length m in all θ(m2) orientations that are relevant. We also show that the number of different orientations which P can have is θ(m3). The text T is scanned with Aho-Corasick string matching automaton to find the occurrences of any of these θ(m2) linear strings of length m. Each such occurrence indicates a potential set of occurrences of whole P which are then checked. Some preliminary running times of a prototype implementation of the method are reported.


Pattern Match String Match Input Text Pixel Color Pixel Boundary 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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Copyright information

© Springer-Verlag Berlin Heidelberg 1998

Authors and Affiliations

  • Kimmo Fredriksson
    • 1
  • Esko Ukkonen
    • 1
  1. 1.Department of Computer ScienceUniversity of HelsinkiHelsinkiFinland

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