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while preserving the distribution characteristics of the initial pattern. The majority
of the existing researches focus on the building typification (Regnauld
2001
; Sester
2005
; Anders
2006
; Burghardt and Cecconi
2007
). Meanwhile, there are a few
researches aiming at linear elements such as drainage system and ditches (Sandro
et al.
2011
; Zhang
2007
). More works remains to be done to promote two oper-
ators, displacement and typification, which were found to be the most problematic
operators during the generalization process (Foerster and Stoter
2008
). Therefore,
the study of typification is challenging and meaningful.
Typification usually consists of two steps. It should begin with the recognition
of the pattern of those objects in groups that are subjected to typification, that is,
classifying those objects or recognizing the specific alignment. For instance, the
classification of the building set and the recognition of the arrangement pattern
such as grid pattern (Anders
2006
), linear pattern and curve pattern (Zhang et al.
2013
). Thereafter, those objects would be represented. In detail, the new objects
would replace the old ones while the initial characteristics, such as direction,
arrangement, and density, are preserved. For example, when the initial building set
is replaced by the new ones, the new direction should be determined according to
the initial average direction.
Following the idea of typification, this paper proposes a method aiming to work
on ditches that run approximately parallel to each other. This method combines
two clustering ideas. One is ditch grouping according to the idea of division, and
the other is considering density variation.
The rest of this chapter is structured as follows.
Section 2
introduces the basic
concepts and characteristics of ditches.
Section 3
describes the method.
Section 4
presents the experimental results and the shortcomings of the method. Conclusions
are drawn in
Sect. 5
.
2 Characterization of Ditches
A ditch is a man made channel that is used to irrigate, conduct, and drain water
(Sandro et al.
2011
). It can be classified as a linear element if only considering its
geometry. As shown in Fig.
1
, some ditches run approximately parallel to each
other (i.e. Fig.
1
a), while some are not (i.e. Fig.
1
b).
The structure and morphological characteristics of the artificial hydrographic
net in irrigated area should be reflected correctly in the map compilation. They
cannot be selected based solely on their length, whereas the monolithic con-
struction should be taken into account. It is obvious that simply using the length of
the ditches or practically choosing one out of two cannot meet the requirement of
the cartographic generalization of those ditches in almost parallel distribution
pattern. To address this issue, this paper proposes an approach to the typification
for this particular case.
