Table 6.127—DRM_Grid_Overlap

Property

Description

Superclass

·         <DRM SEDRIS Abstract Base>

Class

·         <DRM Grid Overlap>

Subclass

·         none

Definition

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:

a. A and B are not disjoint due to any higher-level organizing structure in the transmittal, such as membership under different branches of an <DRM Alternate Hierarchy Related Geometry>, or disjoint <DRM Time Constraints Data>.

b. A and B have matching <DRM Classification Data>.

c. At least one <DRM Table Property Description> in A has a meaning matching a <DRM Table Property Description> in B.

d. Both A and B actually have data for that matching <DRM Table Property Description> at L.

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 DT_OP_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.

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

DT_OP_ADD and DT_OP_MEAN can only be applied to numeric data.

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

STEP 3:

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

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

A

10

0

DT_OP_BASE

B

10

1

DT_OP_REPLACE

A

20

0

DT_OP_BASE

C

20

1

DT_OP_REPLACE

D

20

2

DT_OP_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

DT_OP_BASE

B

1

1

DT_OP_MEAN

M

1

999

DT_OP_ADD

B

2

0

DT_OP_BASE

M

2

999

DT_OP_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.

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)

·         none

Composed of (two-way metadata) (inherited)

·         none

Composed of (two-way metadata)

·         none

Component of (two-way) (inherited)

·         none

Component of (two-way)

·         one <DRM Property Grid>

Constraints

·         none

Notes

none

Class diagram

<DRM Grid Overlap>