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There are two types of digital charts; raster charts and vector charts. A raster chart is simply a scanned image of a paper chart, whereas a vector chart is a digital database of objects, such as points, lines, areas, buoys, etc., that cannot only be displayed as an image on a navigation system, but also queried for additional information.
Chart Updates are provided weekly by means of download, e-mail or on CD. However, updates to individual ENCs are sequential, and the sequence is unique to each ENC. Therefore, during the updating process a type-approved ECDIS always checks that all updates in the sequence have been applied. It alerts the user if an update is missing and prevents further updates to the ENC concerned until the missing update is applied. A type-approved ECDIS maintains a list of updates applied and the date of application. This list can be used to check the update status of the loaded ENCs. If all available ENCs show the same date for the latest update it is most likely that they have not been updated regularly, and the chart distributor should be contacted for verification. Port State Control officers may use the ECDIS listing to ensure that ENCs are being kept up to date in accordance with SOLAS V Regulation 27.
Electronic Chart Display and Information System - An ECDIS is a computer-based navigation information system that complies with International Maritime Organization (IMO) regulations and can be used as an alternative and replacement to paper nautical charts. An ECDIS can replace paper charts only when:
- Official ENCs are loaded and used.
- The system (hardware and software) is type approved according to latest IMO standards (with a wheel mark sticker affixed).
- The crew operating the ECDIS has successfully passed Generic ECDIS Training and Type Specific ECDIS Training.
- A back up has been arranged for, which can be either a second ECDIS, or fully corrected paper charts.
ECDIS Carriage Requirement
The IMO has decided that all existing passenger ships >500 gross tons and all new cargo ships >3,000 gross tons are required to carry ECDIS from their first survey after 1 July 2014. In 12 months time, on 1 July 2015, this will be further extended to include all existing tankers >3,000 gross tons, extending to cargo ships >50,000 GT from 1 July 2016. This will mark a major expansion in the proportion of the merchant fleet that is subject to the mandatory carriage of ECDIS.
Electronic Chart System –Software and hardware displaying electronic navigational charts. An ECS can be used as a navigational aid only and does not replace paper nautical charts.
ENC stands for Electronic Navigational Chart and was originally introduced to signify a digital chart that complied with the IHO chart data transfer standard S-57. By definition, ENCs can only be produced by or on the authority of a government, authorised Hydrographic Office, or another equivalent government institution. The ENC content is based on the source data of the responsible Hydrographic Office and is always referred to the World Geodetic System 1984 Datum (WGS84). ENCs are regularly updated with information that is digitally distributed.
Firstly, ENCs can only be purchased from an authorized distributor who will always supply the ENC as part of a subscription service including the delivery of updates throughout the subscription. Secondly, a type-approved ECDIS can distinguish an ENC from unofficial chart data. If unofficial data is shown on the ECDIS display its boundaries are marked by a special line style. It is a one-sided RED line with a diagonal stroke on the unofficial side of the line. Finally, the mariner can normally use the ECDIS or ECS system to interrogate the chart data and get details, such as chart producer, edition number, update status, etc.
The majority of ENCs are made available to end users in a protected format called IHO S-63. S-63 is designed to maintain the integrity of all transactions between service provider and end user. It also enables the end user’s systems to check the authenticity of the sent data. S-63 ENCs are usually distributed on CD because of the large amount of data. In order to load and display S-63 protected ENCs, the end users need "chart permits" that are normally emailed by their service providers. The chart permits are loaded into the ECDIS and allow the licensed charts to be loaded from the CDs and displayed in the ECDIS. Chart permits need to be renewed whenever the ECDIS is changed, subscriptions are renewed, or additional ENCs are licensed. A few nations (most notably the USA) distribute their data in unencrypted S-57 format, rather than encrypted S-63. All type-approved ECDIS systems are able to load and display S-57 ENCs without chart permits.
International Hydrographic Organization - The IHO is an intergovernmental consultative and technical organization that was established in 1921 to support safety of navigation and the protection of the marine environment. The object of the organization is to bring about:
- The coordination of the activities of national hydrographic offices;
- The greatest possible uniformity in nautical charts and documents;
- The adoption of reliable and efficient methods of carrying out and exploiting hydrographic surveys;
- The development of the sciences in the field of hydrography and in descriptive oceanography.
International Maritime Organization - As a specialized agency of the United Nations, IMO is the global standard-setting authority for the safety, security and environmental performance of international shipping. Its main role is to create a regulatory framework for the shipping industry that is fair and effective, universally adopted and universally implemented.
Official Data / Inofficial Data
Official charts are issued by or on the authority of a government authorized Hydrographic Office or another relevant government institution that may be used to fulfil carriage requirements - provided they are kept up to date by the user. Besides official paper charts there are two kinds of official digital charts commonly available; Electronic Navigational Charts (ENCs) and Raster Navigational Charts (RNCs), of which the most well-known are UKHO ARCS charts. All other nautical charts are by definition unofficial and are often referred to as private charts. These charts are not accepted as a formal basis for navigation under the SOLAS convention.
An electronic chart must conform to standards stated in the International Hydrographic Organization (IHO) Special Publication S-57 before it can be certified as an ENC.
IHO Special Publication S-63 developed by the IHO Data Protection Security Working Group is used to commercially encrypt and digitally sign ENC data. Chart data is captured based on standards stated in IHO Special Publication S-57, and is displayed according to a display format stated in IHO Special Publication S-52 to ensure consistency of data rendering between different systems.
Official charts subject to specific approval of the format concerned and its distribution system, and subject to approval by the producing hydrographic office. The International Hydrographic Organization has approved the direct distribution of ENCs in the internal machine code format used by the individual ECDIS manufacturer. The generic name for this type of distribution is "SENC Distribution" and, depending on the make of ECDIS involved, this can make loading ENCs into an ECDIS significantly easier and faster. ChartWorld is approved to distribute a great number of ENCs in the SevenCs SENC format called "DirectENC."