Table 6.102 — DRM_Grid_Overlap

Property

Description

Class
  • <DRM Grid Overlap>

Superclass

Subclass
  • None.

Definition

An instance of this DRM class specifies how the data provider intended the consumer to resolve data ambiguity at a location falling within a grid cell for two or more <DRM Property Grid> instances, such that the ambiguity cannot be resolved by other means.

An ambiguity occurs at a location L lying within two <DRM Property Grid> instances A and B if all four of the following conditions hold.

When such an ambiguity occurs, <DRM Grid Overlap> instance(s) indicate how the data provider intended the consumer to calculate the <DRM Table Property Description> value intended at each such location.

When <DRM Grid Overlap> instances are required and are present, resolution only occurs within an overlay group. The resolution process is performed on data from <DRM Property Grid> cells that contain a given location (choose the first priority group that includes all relevant grids.) The resolution process is as follows:

STEP 1:

Start with priority 0. Each priority group shall have exactly one <DRM Grid Overlap> instance with priority 0. The <DRM Property Grid> instance for this <DRM Grid Overlap> instance shall overlap the other <DRM Property Grid> instances in the given priority group. The operation for priority 0 shall be BASE.

Extract cell data from the <DRM Property Grid> instance that has this <DRM Grid Overlap> instance as a component; this becomes the current data.

STEP 2:

Find the next priority. Priorities within an overlay group need not be consecutive, but they shall be unique. Extract the cell data from the <DRM Property Grid> that has this <DRM Grid Overlap> as a component. Operate on this and the current data according to the <DRM Grid Overlap> operation. The result of the operation becomes the current data for the next step.

REPLACE means that this data overrides the current data from the last step.

ADD and MEAN can only be applied to numeric data.

MERGE operations are dependent on the classification of the <DRM Property Grids>, and use methods documented outside SEDRIS.

STEP 3:

Look for next priority. If found, goto step 2. Otherwise use the current data.

Class diagram

Figure 6.118 — DRM_Grid_Overlap

Inherited field elements

Field name

Range

Field data type

None

    

Field elements

Field name

Range

Field data type

overlay_group

 

Short_Integer_Positive

priority

 

Short_Integer_Unsigned

operation

 

Grid_Overlap_Operator

Associated to (one-way) (inherited)
  • None.

Associated to (one-way)
  • None.

Associated by (one-way) (inherited)
  • None.

Associated by (one-way)
  • None.

Associated with (two-way) (inherited)
  • None.

Associated with (two-way)
  • None.

Composed of (two-way) (inherited)
  • None.

Composed of (two-way metadata) (inherited)
  • None.

Composed of (two-way metadata)
  • None.

Component of (two-way) (inherited)
  • None.

Component of (two-way)

Constraints

Clarifications

  

Example(s)

  • Low resolution grid A covers a large area, and contains smaller (but higher resolution) grids B, C, and D. The <DRM Grid Overlap> scheme is:

    <DRM Property Grid> overlay_group priority operation
    A100 BASE
    B101 REPLACE
    A20 0 BASE
    C20 1 REPLACE
    D20 2 REPLACE

    In intersection A & B, B data overrides A.
    In intersection A & C, C data overrides A.
    In intersection A & D, D data overrides A.
    In intersection A & C & D, D data overrides others.

    B should not intersect either C or D as this scheme will not provide ambiguity resolution.

  • A seamount is modeled as a grid M of elevation offsets above the underlying bathymetry in grids A and B. The <DRM Grid Overlap> scheme is:

    <DRM Property Grid> overlay_group priority operation
    A 1 0 BASE
    B 1 1 MEAN
    M 1 999 ADD
    B 2 0 BASE
    M 2 999 ADD

    In intersection A & M and outside of B, add M offsets to A bathymetry values.

    In intersection B & M and outside of A, add M offsets to B bathymetry values.

    In intersection A & B, average A and B bathymetry values.

    In intersection A & B & M, first average A and B bathymetry values, and then add offsets from M to the average.