Feature Description

Various features in global oceans (such as lighthouses, ports, shipping channels, etc.) constitute essential components of electronic charts. They provide detailed navigation and geographic information to ensure maritime safety and operational efficiency.

To facilitate data updates, maintenance, and improve data exchange interoperability between systems, each feature requires a unique identification marker.

The IHO electronic chart standard (ENC) defines the structure of the Feature Object Identifier (FOID) field to achieve unique identification. FOID contains the following subfields:

1. Producing agency (AGEN): Identifies the organization producing feature data. Each national/regional maritime authority has a unique code for decentralized global management. For instance, Chinese and American maritime agencies have distinct codes to prevent numbering conflicts.
2. Feature Identification Number (FIDN): A unique identifier assigned to each feature ensuring global uniqueness.
3. Feature Identification Subdivision (FIDS): Further distinguishes subdivisions of features sharing the same identification number.

In S-57 standards, this identifier is also called "Long name". The uniqueness of FOID within the same producing agency is guaranteed by the unique combination of FIDN and FIDS.

In ENC, different instances of the same object may share the same FOID. For example, a feature might be represented as different geometry types (e.g., a shipwreck as line or polygon) across charts of varying scales/purposes while retaining the same identifier. Similarly, when split across different chart cells (equivalent to map sheets), features may share identifiers. However, distinct features must never share duplicate FOIDs, even if a feature has been deleted.

When creating new editable S-57 chart dataset groups or converting read-only groups to editable S-57 chart dataset groups, you must specify FIDN sequence names and FIDS to assign unique FOIDs to new features. FOIDs are automatically generated upon feature creation. Therefore, FIDN sequences must be created for the datasource beforehand to ensure unique identifiers for new features.

Steps

1. In Workspace Manager, right-click the datasource node and select Properties from the context menu to open the Properties window.
2. In the Feature Sequence panel, click the Add button on the toolbar. In the Create Signature Sequence dialog, configure the name, start value, and end value for the feature identification sequence.
3. Click OK to complete FIDN sequence creation. Repeat step 2 to create additional FIDN sequences. Close the Create Signature Sequence dialog when finished.

Related Topics

Chart Data Storage

Create Editable Chart Group

Convert Chart Group