Depth areas (Maritime Charting)

Depth areas are S-57 objects used to depict depth ranges between contours in Electronic Navigation Charts (ENC). The Generate Depth Areas (Selected Feature) tool is used to create these depth areas in a desktop or enterprise production environment. It updates depth areas that exist, creates depth areas as needed, and deletes areas that are no longer relevant based on a given extent and compilation scale. Boundaries of the extent are defined by selecting a polygon feature.

Prior to using the Generate Depth Areas (Selected Feature) tool, several conditions must be met for the tool to attribute correctly. Proper collection of depth contours, closing lines, and group 1 features will ensure that closed areas can be formed and attributed accordingly.

Depth contours

Depth contours establish the geometric limits of each depth area feature. In addition, the VALDCO attribute serves to attribute each polygon depth area with the appropriate depth range, ensuring accurate depiction of the depth profile. Depth contours must be collected so that they form closed areas by snapping to existing skin of earth features, metadata borders, or other available depth contours.

Closing lines

Depth contours derived from a hydrographic source or through traditional charting workflows usually do not completely delineate the boundary of the depth area features to which they correspond. As a result, it is required to close off the boundaries of each depth area so that the geometry needed to completely form the polygon depth area feature exists. To resolve this problem, the ClosingLinesL feature class is provided to hold the additional line work necessary to support the closure of each polygon depth area feature. The tool is aware of the ClosingLinesL feature class and will consider these features when executed. If the depth contour boundary is not closed or is incomplete, the tool will ignore the contour when generating the depth area.

Group 1 (skin of the earth)

There are two groups defined for ENC: group 1 (skin of the earth) and group 2 for all other geometric objects. To create a valid ENC, each area covered with data must be covered with group 1 features that do not overlap each other (the skin of the earth). These features correspond to records with FCSubtype of DEPARE_DepthArea, DRGARE_DredgedArea, FLODOC_FloatingDock, HULKES_Hulk, LNDARE_LandArea, PONTON_Pontoon, and UNSARE_UnsurveyedArea. The tool is aware of all group 1 features within the extent you specify and will leverage their geometry to clip portions of the depth area polygon boundary.

Defining the extent

The extent of the area of interest can be defined by selecting a feature such as a polygon representing the area of a hydrographic survey or a new feature you created. It is recommended that when defining the extent, you do not go outside the area that contains data. If you go beyond the area containing data, the tool may interpret the depth contours as open. The extent of the area of interest contributes to the forming of closed areas, so depth information is available to attribute the depth area (DEPARE_DepthArea) feature output.

Defining depth band values

After the extent of the area of interest is defined, the Generate Depth Areas (Selected Feature) tool will scan existing features to prepopulate the depth band values. You may override these values as needed.

Shallowest depth band or drying height

Drying height, or -H value, is defined in the use of object catalog as H = Height of the coastline datum above sounding datum, or a rounded value (for example, the value of the highest drying contour indicated on the source document or zero if the coastline datum is the same as the sounding datum).

Deepest depth band

Depth bands are determined by the values of the depth contours that occur within the defined area of interest. The deepest depth band typically cannot be determined from that information alone and requires you to input what the upper limit will be for the DRVAL attribution.

Merging depth areas

When the Generate Depth Areas (Selected Feature) tool executes within an area of interest that cuts existing depth area features, you have the option to merge the newly created depth areas with those that preexisted. The attribution must correspond and have the same DRVAL1 and DRVAL2 values for this to be possible. When merging occurs, the original object ID and other identifying attributes will be preserved from the preexisting depth area features. If the Merge Depth Areas check box is unchecked, or based on new attribution the features cannot be merged, then the newly created features will have new identifying attributes.

Generating depth areas in the NIS database

When using the Generate Depth Areas (Selected Feature) tool in the Nautical Information System (NIS) database, the tool will use the compilation scale value setting. The scale of the features used to form the new depth areas must match the compilation scale setting for them to be considered. All other features contained in the NIS will be ignored. The compilation scale value will be assigned to the newly created features using the attribute PLTS_COMP_SCALE. Additionally, all of the features (depth contours, closing lines, and group 1) needed to generate the new depth areas must conform to the same compilation scale.

Description of rules

The attribution of the depth area features created by the tool incorporates the guidance found within the IHO’s use of object catalog. The rule descriptions correspond to the image.

Rule based on bounding depth contours

The following rule applies when sufficient depth contours exist to contribute to the proper attribution of new depth area features.

1. If the depth area is bounded by two or more depth contours:

• DRVAL1 will take the value of the dataset depth contour immediately shallower than the value of DRVAL2.
• DRVAL2 will take the value of the deepest depth contour bounding the area.

Rules that rely on soundings

Soundings will be used to assist in the attribution of the newly created depth areas.

注:

Soundings that have the attribute EXPSOU defined as either shallower or deeper than the surrounding depth area will not be used to determine attribution.

2. If the deepest depth is shown by a depth contour, and the shallowest depth is shown by a sounding (a shoal):

• DRVAL1 will take the value of the dataset depth contour immediately shallower than the value of the sounding or -H.
• DRVAL2 will take the value of the depth contour.

3. If the deepest depth is shown by a sounding and the shallowest depth is shown by a depth contour (a deep):

• DRVAL1 will take the value of the depth contour.
• DRVAL2 will take the value of the dataset depth contour immediately deeper than or equal to the value of the sounding.

Rules that do not rely on soundings

When no soundings are present, the adjacency to land area, encoding of surrounding depth areas, and those of the bounding depth contours will be used to determine the attribution of the newly created depth areas.

4. If the shallowest depth is defined by the coastline:

• DRVAL1 will take the value of -H.
• DRVAL2 will take the value of the shallowest dataset depth contour bounding the area.

注:

Rule 4 was altered in two ways to control how it is enforced:

• DRVAL1 will only take the value of -H when the bounding depth contour has a value of 0. This is to limit the creation of foreshore areas when they do not make sense.
• It will only apply when rules 1, 2, or 3 cannot be applied. Many times depth areas have one or more of their borders defined by land area, so the use of rule 4 will result in incorrect attribution.

5. If the depth area is bounded by only one depth contour, contains no soundings, and is a shoal:

• DRVAL1 will take the value of the dataset depth contour immediately shallower than the value of the depth contour, or -H.
• DRVAL2 will take the value of the depth contour.

6. If the depth area is bounded by only one depth contour, contains no soundings, and is a deep:

• DRVAL1 will take the value of the depth contour.
• DRVAL2 will take the value of the dataset depth contour immediately deeper than the value of the depth contour.

Rules that involve incomplete contours

The following rules will apply when incomplete contours exist and do not form a closed area.

7. If the depth area is bounded by an incomplete depth contour on one side (such as an incompletely surveyed area) and a complete depth contour on the other: This area is optional and the tool ignores the depth contour.

8. If the depth area is bounded by complete depth contours, but contains an incomplete (floating) depth contour:

• DRVAL1 will take the value of the shallowest depth contour.
• DRVAL2 will take the value of the deepest depth contour.