A New Simplification Approach Based on the Oblique-Dividing-Curve Method for Contour Lines

Haizhong Qian,Meng Zhang,Fang Wu

doi:10.3390/ijgi5090153

Abstract

As one of the key operators of automated map generalization, algorithms for the line simplification have been widely researched in the past decades. Although many of the currently available algorithms have revealed satisfactory simplification performances with certain data types and selected test areas, it still remains a challenging task to solve the problems of (a) how to properly divide a cartographic line when it is too long to be dealt with directly; and (b) how to make adaptable parameterizations for various geo-data in different areas. In order to solve these two problems, a new line-simplification approach based on the Oblique-Dividing-Curve (ODC) method has been proposed in this paper. In this proposed model, one cartographic line is divided into a series of monotonic curves by the ODC method. Then, the curves are categorized into different groups according to their shapes, sizes and other geometric characteristics. The curves in different groups will trigger different strategies as well as the associated criteria for line simplification. Whenever a curve is simplified, the whole simplified cartographic line will be re-divided and the simplification process restarts again, i.e., the proposed simplification approach is iteratively operated until the final simplification result is achieved. Experiment evidence demonstrates that the proposed approach is able to handle the holistic bend-trend of the whole cartographic line during the simplification process and thereby provides considerably improved simplification performance with respect to maintaining the essential shape/salient characteristics and keeping the topological consistency. Moreover, the produced simplification results are not sensitive to the parameterizations of the proposed approach.

Highlights

Following the developments of information techniques, it became necessary to automate tasks that were previously manual such as map generalization between various representations used for digital cartography and/or geographical information science (GIS)
A new line-simplification approach based on the Oblique-Dividing-Curve (ODC) methIondthhaissabretiecnlep, raonpeowsedlin
Divided into a chain of shorter curves by the ODC method. According to their geometric characteristics regarding shapes and sizes, the curves are categorized into four groups: “large U-shaped”, “large V-shaped”, “small” and “minimum”

Summary

Introduction

Following the developments of information techniques, it became necessary to automate tasks that were previously manual such as map generalization between various representations used for digital cartography and/or geographical information science (GIS). Nabil Mustafa et al [18] presented a so-called Voronoi diagram method, which first divides a complex cartographic curve into a series of safe sets and simplifies each safe set by using the algorithms such as DP and VW. In this way, it avoided intersections among the lines input. IInn tthhee pprrooppoosseedd lliinnee--ssiimmpplliiffiiccaattiioonn aapppprrooaacchh,, tthhee ccuurrvveess ddiivviiddeedd bbyy tthhee OODDCC mmeetthhoodd wwiillll bbee ccllaassssiiffiieedd iinnttoo ddiiffffeerreenntt ggrroouuppss ffoorr ffuurrtthheerr pprroocceessssiinnggaaccccoorrddiinnggttoobbootthhoofftthheeiirrsshhaappeessaannddssiizzeess

Identiffiication of the U and V--sshhaappeeddCCuurrvveess

Customized Simplification Methods for Different Kinds of Curves

Schematic Process of the Overall Line Simplification

Comparison of Different Division Methods on the Same Cartographic Line

Conclusions