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Quantifying Distances from Points to Polygons - Applications in Determining Fetch in Coastal Environments

Mika Murtojärvi, Tapio Suominen, Harri Tolvanen, Ville Leppänen, Olli Nevalainen, Quantifying Distances from Points to Polygons - Applications in Determining Fetch in Coastal Environments. Computers & Geosciences 33(7), 843-852, 2007.

Abstract:

Distance from a point to adjacent borderlines is a variable that has many
applications in environmental research. Geographical information systems
(GIS) include tools for measuring such distances, but these tools are
inefficient if there are multiple, i.e. millions of distances to be
calculated. In this paper we propose an efficient algorithm which
calculates the distances in multiple predetermined directions from a
large number of points to polygon borders.


The problem is significantly simplified by the fact that the distances
are calculated in some directions, only. An interval tree is utilized for
efficiently retrieving those line segments describing the coastal lines
and the borders of the islands that are relevant in determining these
distances. The algorithm is also robust so that it gives meaningful
results in the presence of rounding errors regardless of the positions of
the study points with respect to the polygon borders. In coastal
environments the straight-line distance from a point to the nearest
shoreline over an open water surface is referred to as fetch length. The
fetch lengths in multiple directions indicate general openness around a
studied point and it may also be used as a variable in wave power
calculations. An implementation of the algorithm was used for calculating
fetch data for the archipelago of SW-Finnish coast in the Baltic Sea. The
map data contained 3 million vertices and fetch lengths were calculated
for 2.5 million points in 48 directions. The algorithm enabled
determining fetch lengths in the complex archipelago environment quickly
in high spatial accuracy and it may have applications also in other
geographical research and image processing.

BibTeX entry:

@ARTICLE{jMuSuToLeNe07a,
  title = {Quantifying Distances from Points to Polygons - Applications in Determining Fetch in Coastal Environments},
  author = {Murtojärvi, Mika and Suominen, Tapio and Tolvanen, Harri and Leppänen, Ville and Nevalainen, Olli},
  journal = {Computers & Geosciences},
  volume = {33},
  number = {7},
  pages = {843-852},
  year = {2007},
  keywords = {Efficient algorithms; GIS; Fetch length; Exposure; Computational geometry},
}

Belongs to TUCS Research Unit(s): Algorithmics and Computational Intelligence Group (ACI)

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