What factors affect the accuracy of ship's position on electronic nautical charts

Since human civilization has possessed the technology of navigation, one of the major concerns of navigators has been the exact position of a ship in the sea. In order to obtain the ship's position, navigators have had to use celestial bodies/landmarks/radio signals, etc. to obtain the ship's position line, and then plotted the ship's position line or digital ship's position markers on the charts to obtain the intuitive ship's position. According to the acquired ship's position, the pilot can judge the safety of navigation and whether the ship is sailing on the planned route. In the process of practical operation, the pilot often spends more time on observation and marking, and the judgment of the safety of navigation is often carried out only after the observation and marking. That is to say, using this way of obtaining the ship's position by marking on the charts, it is difficult for the pilot to get the intuitive and immediate ship's position, and the intuitive ship's position marked by the pilot is the ship's position at the moment of observation rather than the immediate ship's position, which results in a lag in obtaining the ship's position. If in the ocean this lag influence is not very big, if the near shore navigation time will have a great influence on the ship's safety.

Electronic charts are able to solve the phenomenon of lag in obtaining ship's position arising from positioning on traditional paper charts, and can automatically display the immediate ship's position on the charts instantly, so that the driver can judge the safety of the ship's navigation according to the display of the immediate ship's position in a continuous manner; what is more beneficial for the use of electronic charts is that the ship's position obtained through the GPS/DGPS is uninterrupted, which makes the use of electronic charts advantageous. The use of electronic charts is further facilitated by the fact that the ship's position obtained by GPS/DGPS is uninterrupted, giving the use of electronic charts a favorable technical guarantee. A good pilot or team can get a position every 3 minutes at best, and an electronic charting system can get a more accurate and reliable position every second.

Electronic charts can also integrate and process other navigational aids, such as the ship's heading/speed/depth sounder and radar data, which are displayed on the instrument along with the instantaneous ship's position; and all these information can be set up as alarm ranges, which can alert the pilot of potential navigational hazards in advance, thus ensuring the safety of the ship's navigation.

All in all, with the help of electronic charts, the driver will have a clear picture of the immediate ship dynamics and any dangers in the navigation area, and at the same time, with the help of radar observation, he will also have a clear idea of the dynamics of the surrounding ships; "Knowing the enemy and knowing yourself is never in danger", and he will know the situation clearly. Knowing oneself and the surrounding situation clearly, the safety of navigation will have a strong guarantee. For the electronic nautical charts the following will focus on the discussion of its types, methods of use, characteristics, role and some of its limitations and so on.

Types of electronic charts

1. Terminology related to electronic charts

Before we understand what electronic charts are, we need to master some terms and definitions. We must distinguish what is official charts and unofficial charts. Official charts refer to the charts surveyed and drawn by the government-authorized hydrographic department, while unofficial charts refer to the charts drawn by some civil organizations, and unofficial charts are somewhat different from the official charts in terms of the drawing standards and the accuracy of the data.

ECS: Electronic Chart System (electronic chart system abbreviated as ECS) is a commercial electronic charting system, she is not fully applicable to the International Maritime Organization's SOLAS Convention requirements. ECS is mainly used for navigational aids, but also as a supplement to the functional deficiencies of paper charts.

ECDIS: Electronic Chart Display and Information System (An electronic chart display and information system abbreviated as ECDIS) is an electronic charting system that uses electronic navigational charts or other charts with similar functions (e.g., NIMA digital navigational charts) and is fully applicable to the requirements of the SOLAS Convention. ECDIS is an electronic charting system that uses electronic navigational charts or other functionally similar charts (e.g. NIMA digital navigational charts) and fully applies the requirements of the SOLAS Convention.

EC: An electronic chart (EC) is a digital chart that can be displayed on a computerized navigational aid.

ECDB: An electronic chart data base (ECDB) is a database for the production of electronic charts.

ENC: An electronic navigational chart (abbreviated as ENC) is a standardized electronic chart issued by a state-authorized hydrographic office.

ENCDB: The electronic navigation chart database (The electronic navigation chart database, abbreviated as ENCDB) is the database for the production of electronic navigation charts.

SENC: The system electronic navigation chart (The system electronic navigation chart abbreviation for SENC) is the electronic chart display and information system database.

RNC: A raster navigation chart (RNC) is a raster navigation chart issued by the state-authorized hydrographic department. A raster navigation chart (RNC) is an electronic copy of a paper chart that is scanned in a single pass to form a single digital file of information, which can be thought of as an electronic replica of the paper chart.

RCDS: A raster chart display system (abbreviated as RCDS) is a system for displaying official raster charts on ECDIS (Electronic Chart Display and Information System). Raster charts are not a substitute for traditional paper charts because the characteristics of such charts cannot be adapted to IMO requirements, and therefore ECDIS can only use raster charts in ECS mode.

The display of electronic nautical charts can be done at large and small scales respectively. If you want to display a large scale, you can operate the display to make the content closer and then the scale of the display is enlarged, of course, this kind of large scale display is also based on a certain accuracy of the chart, and not the larger the display the higher the accuracy. Therefore, it is better to use large scale display in some dangerous areas.