Depth Contours and Coastline Generalization for Harbour and Approach Nautical Charts

Andriani Skopeliti,Lysandros Tsoulos,Shachak Pe’Eri

doi:10.3390/ijgi10040197

Abstract

Generalization of nautical charts and electronic nautical charts (ENCs) is a critical process which aims at the safety of navigation and clear cartographic presentation. This paper elaborates on the problem of depth contours and coastline generalization—natural and artificial—for medium-scale charts (harbour and approach) taking into account International Hydrographic Organization (IHO) standards, hydrographic offices’ (HOs) best practices and cartographic literature. Additional factors considered are scale, depth, and seafloor characteristics. The proposed method for depth contour generalization utilizes contours created from high-resolution digital elevation models (DEMs) or those already portrayed on nautical charts. Moreover, it ensures consistency with generalized soundings. Regarding natural coastline generalization, the focus was on managing the resolution, while maintaining the shape, and on the islands. For the provision of a suitable generalization solution for the artificial shoreline, it was preprocessed in order to automatically recognize the shape of each structure as perceived by humans (e.g., a pier that looks like a T). The proposed generalization methodology is implemented with custom-developed routines utilizing standard geo-processing functions available in a geographic information system (GIS) environment and thus can be adopted by hydrographic agencies to support their ENC and nautical chart production. The methodology has been tested in the New York Lower Bay area in the U.S.A. Results have successfully delineated depth contours and coastline at scales 1:10 K, 1:20 K, 1:40 K and 1:80 K.

Highlights

The cartographic rules are different for depth areas and contours in paper charts and their digital form compared to electronic nautical charts (ENCs)
The research presented in this paper aims to cover specific gaps in depth contours and coastline generalization identified through a literature review and in nautical chart production environments
It proposes a generalization methodology that utilizes both depth contours already depicted in nautical charts and those extracted from digital elevation models (DEMs) and ensures integration with generalized soundings

Summary

Introduction

The cartographic rules are different for depth areas and contours in paper charts and their digital form (raster navigational chart) compared to electronic nautical charts (ENCs). Cartographers extract contours (and soundings) for portrayals on nautical charts from these data sources. The two main reasons are the data volume and the resulting shape of the depth contours that need to contain all soundings within a value range of the two bounding contours. High-resolution accurate coastline data are collected from detailed light detection and ranging (lidar) survey measurements, high-resolution tidally-referenced imagery and topographic surveys. The coastline needs to be generalized according to chart scale [2]. The purpose of depth contours and elevation points in a nautical chart are different than those of a topographic map. Standards, constraints and existing practices for depth contours and coastline generalization are reviewed

Objectives

Methods

Results

Conclusion