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data are not permitted. If the tool generating the Subordinate Bathymetry component does not support the optional Mesh Type, the optional second channel of the file need not be created; in
which case the TIFF file becomes a single channel image.
5.6.1.8.4 Supported Compression Algorithm
The CDB standard supports the LZW compression algorithm for the Subordinate Bathymetry component. Consider compressing the file if its content is not of type floating-point.
5.6.1.9 Subordinate Alternate Bathymetry Component
The Subordinate Alternate Bathymetry component is similar to the Primary Alternate Terrain Elevation component: it provides a better delineation of the shoreline and bottom of water bodies
such as oceans, lakes, and rivers. To do this, the Subordinate Alternate Bathymetry component encodes information that re-positions each depth samples anywhere within its assigned grid
element. In other words, the “phase” of each bathymetry depth sample can be specified along the latitude and longitude axes. In effect, the Subordinate Alternate Bathymetry component
provides the means to locally increase the precision of the modeled representation of the floor of water bodies. Again, it is expected that the SE tools produce the Subordinate Alternate
Bathymetry component by considering constraint points, lineals and polygons provided by the modeler.
The constituents of the Subordinate Alternate Bathymetry are the depth and mesh type at the specified latitude and longitude offsets inside each grid element. These four constituents are
represented as 4 channels of a TIFF image.
5.6.1.9.1 Data Type
Requirement 97
http:www.opengis.netspeccdb1.0core subordinate-alternate-bathymetry-data-type
The first channel of the TIFF image SHALL contain the Depth component and SHALL be represented as a floating-point or signed integer value. Integer values for tiles at LOD
larger than 0 are scaled according to the following formula:
Integer samples can make use of TIFF’s 8-bit, 16-bit, or 32-bit representation.
The second channel of the TIFF image SHALL contain the Mest Type and SHALL be stored as an unsigned 8-bit integer.
The third channel of the TIFF image SHALL contain the Latitude Offset and SHALL be stored as an 8-bit unsigned integer value ranging from 0 to 255. The value is scaled so
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that each grid element is fragmented in 256 equal parts in the latitude direction. Thus, the grid post cannot be positioned on the latitude of the next grid element directly north of the
current grid element.
The fourth channel of the TIFF image SHALL contain the Longitude Offset and SHALL be stored as an 8-bit unsigned integer value ranging from 0 to 255. The value is scaled so
that each grid element is fragmented in 256 equal parts in the longitude direction. Thus, the grid post cannot be positioned on the longitude of the next grid element directly east
of the current grid element.
5.6.1.9.2 Default Read Value
Simulator client-devices should assume a Depth of zero as well as a Latitude and Longitude Offsets of zero and a Mesh Type of zero when the Subordinate Alternate Bathymetry
component is not available.
5.6.1.9.3 Default Write Value
The files associated with the Subordinate Alternate Bathymetry component for an area covered by a tile at a given LOD need not be created if the source data is not available. Tiles partially
populated with data are not permitted.
5.6.1.9.4 Supported Compression Algorithm
The CDB standard supports the LZW compression algorithm for the Subordinate Alternate Bathymetry component. Consider compressing the file if its content is not of type floating-
point.
5.6.1.10 Subordinate Tide Component
