Digital Revolution of Navigation -

Since ECDIS systems and used ENC (Electronic Navigational Chart) data are quite complex , a number of standards have been produced. There are technical specifications and display standards for ECDIS, and also ENC product specifications and standard for the exchange format of the data. The last ones are known as S-57, and for the moment it is out in its third edition.

Even if ECDIS are rather complex systems they are "stand-alone" systems on one ship, there is no interaction with other ships or traffic control centres. Among other countries, Sweden and Finland take active part in the development of a way to manage this interaction with Vessel Traffic Service Systems (VTS) and Environmental and Traffic Information Systems (ETIS).

National hydrographic offices are explicitly responsible for production and authorisation of ENC data in their waters. In Finland and Sweden this task has been tackled by a joint development project for Hydrographic Information System (HIS). Hydrographic offices are also responsible for delivery of ENC data and updates to customers (i.e. ECDIS operators) in a reliable and cost-effective way. The United Kingdom and Norway have established Northern Europe Electronic Navigational Chart Coordinating Centre (RENC/NE) for commercially-based service for the storage and distribution of ENC data. These services will be made available on CD ROM, ISDN, Inmarsat B High Speed and GSM mobile telephones. Both Sweden and Finland have joined the RENC/NE and are working in the related development projects.

Historical Background

As the result of the technological development during the 1980's the hydrographic community became aware of the future demand for nautical charts in computer assisted navigational systems. This awareness lead to a first meeting in Canada where this topic was discussed. After this a lot of meetings have taken place, work groups have been put together and standards have been produced. All this has lead to the concept of ECDIS (Electronic Chart Display and Information System

Standards

• Specifications for Chart Content and Display Aspects of ECDIS (IHO S-52)

• IHO Transfer Standard for Digital Hydrographic Data (IHO S-57)

• Electronic Chart Display and Information System - Operational and Performance Requirements Methods of Testing and Required Test Results (IEC 1174)

Chart content and display standard (S-52)

Figure 1. Extraction from test database shown according to S-52

Transfer Standard (S-57)

• Theoretical background, definitions and conceptual model.
• Object Catalogue, which describes all allowed objects; who they are , their definitions and which attributes that are allowed for the objects.
• Attribute Catalogue, which describes all allowed attributes; who they are, their definitions and in some cases also what values that are allowed.
• Description of the transfer format.
• Product specifications, describes what objects and attributes that are allowed for the different products. ENC (Electronic Navigational Chart, data to the ECDIS-systems) is one product. S-57 also deals with exchange of paper charts as well as survey information.

Performance requirements (IEC 1174)

Figure 2. Components in an ECDIS system

ECDIS and future developments

Another name of a traffic control centres is Vessel Traffic Centres (VTS). These centres are monitoring the traffic in a certain area, i.e. areas with very dense traffic, important fairways and harbours etc. The first VTS in Sweden is situated in Malmö (on the south-west coast). Its task is to control the traffic during the construction of the bridge between Malmö and Copenhagen, and later during operation of the bridge. Naturally the VTS will use digital nautical charts for display of the vessels.

What does ENC stand for?

• production of official₁ Electronic Navigational Chart (ENC)₂ data
• infrastructure to deliver ENC
• updating service

₁ national Hydrographic Offices (HO) are exclusively responsible for production and authorisation of ENC data in their waters

₂ only data, which conforms to IHO S-57 standard edition 3, can be considered as ENC

What makes ENC so special?

The main technical characteristics of the S-57e3 compliant ENC are:

• ENC data must be encoded using chain-node topology, duplication of coincident linear geometry is prohibited.
• The horizontal datum must be WGS 84 and no projection is used
• Only binary implementation must be used for ENC. The use of compression algorithms is prohibited, but ENC data may be protected from unauthorised access by the use of encryption algorithms.
• S-57e3 allows for feature-based incremental updating of ENC. Since each object and attribute as well as each geometric element are assigned with unique identifiers, update files containing commands to insert, delete or alter specific features can be incorporated to the existing ENCs in the ECDIS systems without need for changing the whole ENC cell. This provides a great saving in data volume involved in an updating process. (Figure 3.)

Figure 3. A rough example of an incremental updating of ENC

ENC running the gauntlet

Reasons for this state of affairs are at least three-fold:

• S-57e3 standard was officially accepted very late, November 1996
• Since both applicable data structure and product specifications state very complex rules for ENC, requirements for the ENC production system development are extremely high.
• It has become evident that HOs only seldom have needed resources and knowledge in terms of in-house ENC production system development. Therefore many HOs are in hands of software suppliers.

HIS solution for ENC production

HIS project will, among all its other tasks (Figure 4.), cover the requirements for the ENC production by developing tools and processes for extracting appropriate features from HIS central data storage (= seamless SDE database containing all feature objects and spatial presentation to them) according to the predefined ENC product definitions (e.g. cell boundaries) to ENC data sets, and by processing these further into IHO S57e3 compliant transfer files.

Figure 4. ENC production line as a part of the Hydrographic Information System concept

One ENC file will contain data within a defined geographical area, the cell. Since HIS is based on a seamless data base, special care has to be taken of mapping between HIS Feature identifiers and ENC output file specific Record identifiers. It must also be possible to issue updates also for features that have been split by cell boundaries. Final file conversion must also include creation of data set descriptive records, which contain meta data i.e. information that is specific to the file, e.g. description and location of the real-world entities. S-57 Transfer file (ENC data set resulting of the conversion) must be stored to appropriate directory as a base cell file (EN) or update cell file (ER).

Firm Quality Control guarantees the safety of navigation

• landmarks in water
• submarine cables on land
• depth contours crossing
• depth areas not closing

The ENC production line will be controlled by a workflow management system. Procedure descriptions are stored as flow diagrams and stored in a workflow library. ENC operator actions are guided by these procedure descriptions and job status reports are always available to system administrators and authorised users.

Never-ending story

How to reach the navigator on-ship?

Figure 5. WEND model and the ECHO partners

European Chart Hub Operations (ECHO) -project

ECHO will establish a telematics infrastructure to link Hydrographic Offices (HO), a Regional ENC Centre (RENC) and the end-users (ECDIS) to disseminate electronic chart and related information. An ENC Service Specifications will be developed defining the basic transactions that can take place between the data distributor and end user. They cover:

• requests and deliveries of ENC cells and updates
• services related to product availability, status and coverage
• services to receive decryption permits to access ENC information