Colour Table Group

The SEDRIS Data Representation Model APPENDIX A - Classes Colour Table Group

Class Name: Colour Table Group

Superclass - <SEDRIS Abstract Base>

Subclasses

This DRM class is concrete and has no subclasses.

Definition

An instance of this DRM class specifies an interchangeable group of one or more <Colour Table> instances. The primary <Colour Table> instance in the group is indicated by the primary_table_index. When a reference is made to a <Colour Table> instance (for example, from a <Colour Index> component of a <Polygon> instance), the reference identifies the <Colour Table Group> instance and the index within the <Colour Table> instance, but not the specific <Colour Table> instance within the <Colour Table Group> instance. By definition, a <Colour Index> instance refers to a <Primitive Colour> instance from the primary <Colour Table> instance of the indicated <Colour Table Group> instance. An alternate <Colour Table> instance from within the <Colour Table Group> instance can be chosen at the discretion of the data consumer.

Primary Page in DRM Diagram:

Secondary Pages in DRM Diagram:

Example

Consider a <Colour Table Group> instance G with two <Colour Table> components, where the first <Colour Table> component A is for OTW viewing, and the second <Colour Table> component B is for a view as seen through night vision goggles. A <Colour Index> instance associated to G shall reference A if index = 1 but shall reference B if index = 2.
A data provider is required to provide three alternate colour tables for a particular set of environmental data. A <Colour Table Group> instance with three <Colour Table> components with the same usage of OTW is provided. One <Colour Table> component defines the colours as originally created by the data modellers. The second <Colour Table> component has different shades of blue for the lakes and skies that are preferred by one set of customers. The third <Colour Table> instance contains yet another set of blues for the lakes, and different shades of green for the trees preferred by a different set of customers. The data provider identifies the first <Colour Table> component as the primary <Colour Table> component for the group.
Consider a <Colour Table Group> instance with three <Colour Table> components: one for an OTW view, one for a radar view, and one for an infrared view. Each of the three <Colour Table> components contains 234 <Primitive Colour> components. Entry 234 in each <Colour Table> component in this example is a <Primitive Colour> component for the representation of granite, where that in the first <Colour Table> component represents granite in the OTW domain, that in the second <Colour Table> component represents granite in the radar domain, and that in the third <Colour Table> component represents granite in the infrared domain.

FAQs

Can a transmittal in any way refer to a <Colour Table> instance component of a <Colour Table Group> instance other than the primary <Colour Table> component?: No. The only <Colour Table> component that can be referenced of any <Colour Table Group> instance is the primary <Colour Table> instance.
Since they cannot be referenced, why bother to have alternate <Colour Table> instances within a <Colour Table Group> instance?: Because in real life, many run-time systems do have multiple colour tables they can switch between for various reasons, and these tables should be shared to promote interoperability. See the example section, below.