Topology and DNC (Maritime Charting)

Topology is a set of rules that allows you to accurately model geometric relationships. Topology enforces spatial integrity by defining relationships between features.

Topology is only enforced when you validate it. When the topology is validated, the following occur:

• Clustering—The cluster tolerance is the minimum distance between vertices of features that are not coincident. Vertices that fall within the cluster tolerance are defined as coincident and snapped together during the clustering process.
• Cracking—Cracking adds vertices at the intersection of feature edges.
• Rule validation—Once the data has been clustered and cracked, the topology rules are validated and errors are logged.

Validation

Validation takes the longest when you run it for the first time. The first validation checks every feature in the database. Subsequent validations only check dirty areas (areas where edits took place).

DNC Rule base

If you have rules that require specific features to exist to validate another feature, you get false errors. For example, if a rule depends on the existence of Dqyarea but you validated before that feature was created, you have a lot of errors that would not exist if you created the feature first.

A rule in DNC that almost always has an exception is that the boundary of GroundSurfaceElementAS in Ecrarea must be covered by CoastL. Where the GroundSurfaceElementAS meets the Dqyarea edge, there is no coastline, so this error is marked as an exception.

Depending on what stage of production you are in, you may or may not want to correct the error when it is identified. The context menu gives correction options that automatically fix the problem when chosen.

Note:

You should only validate after your chart has been collected and you have made topological edits.

Error Inspector

Once you have made edits to a feature that participates in a topology and validated your edits, you may see one or more topology errors. You can manage topology errors with Error Inspector.

The Error Inspector lets you view topology errors in a table that tells you the rules violated, the feature class or classes involved in the errors, the geometry of the errors, the feature IDs of the features involved in the errors, and whether or not the errors have been marked as exceptions. You can sort the errors by any of the fields in the table so that you can work with all the errors of a given type. You can also limit the errors shown in the table to errors of a given type, errors that occur in the currently visible map extent, or errors that have been marked as exceptions.

In addition to letting you view and sort errors, the Error Inspector lets you select errors, pan or zoom to selected errors, and apply topology fixes of various types to errors. The Error Inspector also allows you to use keyboard shortcuts.