2.2.7 Analysis and development of chart display in electronic chart system-data layering and display classification

Chart display refers to the visualization of chart data (points, lines and surfaces) for users to consult. Compared with paper charts, electronic charts have the characteristics of information diversity and flexibility.

The diversity of information may include:

The demonstrated flexibility may include:

Electronic chart display has the same rules as paper chart projection, but it is different from paper chart once forming. Electronic chart can selectively display the required data in layers at any time according to different navigation requirements. Electronic chart drawing is actually layer by layer, such as drawing shoals first, then land, then mountain lines, and finally drawing lighthouses on blank charts. All data in electronic chart system, including chart information, radar information and ship /AIS information, are displayed in layers and priority management according to S-52 standard. In the process of display, when objects overlap in space, priority should be given to ensuring that high-level information can be displayed clearly and completely, and low-level information cannot cover its previous information.

In the S-52 standard, ECDIS should divide the processed data into at least 10 levels (there may be multiple object elements in the same level or multi-level information), and the classification information is as follows:

After chart analysis, the display priority of each object is obtained through the display library, and the objects with low priority are drawn first, and then the objects with high priority are drawn; Within the same level, draw in the order of face, line and point. The display priority of each object is preset and stored in related files, and users of electronic chart system do not need and cannot change the display priority of some objects.

Due to the diversity of navigation data, the comprehensive display on a limited screen may present a confusing situation. Theoretically, electronic chart belongs to vector data, and whether to display any data can be selected by the end user. However, excessive freedom sometimes makes the primary users at a loss, and if the wrong operation hides the information related to navigation safety, it will have serious consequences. Therefore, the display of electronic chart information is controlled at three classification levels, which is convenient for navigators to screen and view the chart display information.