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Summary Improving Hydrographic Information Zones of Confidence (ZOC) for New Zealand

Improving Hydrographic Information

Zones of Confidence (ZOC) for New Zealand

By: K. Smith, HSA Systems Ltd, G. Cox Discovery Marine Ltd

Summary

In July 2004 HSA Systems Ltd (HSA) commenced an 18 month project for Land

Information New Zealand (LINZ) to assess and assign Zones of Confidence (ZOCs) to all

hydrographic surveys incorporated within 138 hydrographic charts of New Zealand. The

project required each hydrographic survey to be assessed in relation to the data quality

aspects of the International Hydrographic Organisation (IHO) S-57 Standard. During the

survey assessment process the project team was cognisant of the Australian Hydrographic

Service, RAN recommendations and experience with ZOC assessment. The application of

an extensive local knowledge of hydrographic surveying practices undertaken in New

Zealand was crucial to the project.

This paper will describe the process by which HSA assessed in excess of 1,792

hydrographic survey fair sheets and allocated 1,465 ZOCs to survey areas. ZOC metadata

and polygon coordinates were captured using the IHO S-57 version 3.1 format prior to

export in eXtensible Markup Language (XML) format.

Introduction

To date, New Zealand has provided quality indicators on all of its hydrographic charts by way of Source Data Diagrams and Diagrams of Sounding Line Density. To address the current hydrographic data quality requirements, LINZ required the capture of ZOC information for their hydrographic surveys. LINZ (2004) contracted HSA to undertake this project with the project outcomes being:

?Provide a detailed understanding of the quality of all hydrographic surveys used in the compilation of New Zealand’s larger scale nautical charts;

?Improve the survey prioritisation process; and

?Allow for the future depiction of ZOC diagrams on LINZ’s paper charts and electronic navigational charts (ENCs).

The purpose of this paper is to provide an overview of how the ZOC information was acquired including a discussion on the data sources, assessment and encoding approach.

Zones of Confidence (ZOC’s)

A concise history of the development of ZOCs and their adoption by the International Hydrographic Organisation (IHO) is described by Johnson (2004). Aspects of Johnson’s paper are briefly restated here in order to provide an overview of ZOCs. During the 1990’s the concept of ZOCs was developed by the Australian Hydrographic Office (AHO). The IHO Data Quality Working Group (DQWG) developed ZOCs as a technically feasible solution for the assessment and display of hydrographic data quality to support safe and efficient navigation.

The method of encoding data quality information as a Zone of Confidence (ZOC) is contained within the IHO Special Publication No. S-57, Transfer Standard for Digital Hydrographic Data, which includes the Feature Object “M_QUAL” and the attribute “CATZOC” – Category of Zone of Confidence in Data (ZOC).