A note on Feature Codes

74 © 2016 Open Geospatial Consortium

3.3.8 Terms and Expressions

When referring to 3D Models, this standard makes use of a number of terms and expressions that are frequently mentioned throughout the text; these terms and expressions are defined below.

3.3.8.1 Feature Classification

The CDB standard has an important Feature Data Dictionary FDD whose origins are traceable to the DIGEST v2.1 Specification. However, the current FDD is a consolidation of the DIGEST, DGIWG, SEDRIS, and UHRB dictionaries. The CDB FDD makes use of feature codes 23 to classify features. To provide an even better classification of features, the CDB standard defines an additional attribute called the feature sub-code FSC. By extending the feature code hierarchy structure in this manner, it is possible to define a broader set of model types. The sub- code value and its significance depend on the primary feature code. Refer to CDBMetadataFeature_Data_Dictionary.xml for the complete list of feature codes and subcodes. Feature Code aka FACC and FSC are two CDB attributes defined in sections 5.7.1.3.24 and 5.7.1.3.25 respectively. One of the uses of feature codes is to create a hierarchy of subdirectories by taking advantage of the manner in which a Feature Data Dictionary is built. In CDB, a feature code is a 5-character code where the first character represents a category of features, the second represents a subcategory of the current category, and the last three characters represent a specific type in the subcategory. The CDB standard uses these three parts to compose the following hierarchy of folders: \A_Category\B_Subcategory\999_Type\ Where A is the first character of the feature code, Category is the category name, B is the second character of the feature code, Subcategory is the subcategory name, 999 are the 3 rd , 4 th , and 5 th characters of the feature code, and Type feature type as per CDBMetadataFeature_Data_Dictionary.xm l.

3.3.8.1.1 A note on Feature Codes

Feature codes provide a means for encoding real-world entities or objects and concepts, including those which are not necessarily visible or have a tangible physical form e.g., airspace. Featuture codes allow a standardized way to describe the world in terms of features, attributes and attribute values. Feature codes do not specify the delineation or geometry of features. Attributes are the properties or characteristics associated with features. A standardized dictionary is required to support encoding in order to maximize interoperability and to understand the production, exchange, distribution, and exploitation of digital geographic data. 23 In CDB Version 1, Feature Codes were orginally based on the FACC see section 3.3.8.1.1. Future versions of CDB will enhance and extend the capability to allow use of other feature code vocabularies. 75 © 2016 Open Geospatial Consortium Feature codes are defined and stored in a dictionary of features, attributes and attribute values organized in a standardized coding system 24 . Feature codes have not been developed to satisfy the requirements of any single application, product, or data store. Feature codes are intended to be independent from level of resolution scale, representation, or portrayal. The appropriate selection of features codes and attributes are intended to be implemented as part of the overall solution for an application, by means of a database supported by a data schema or model, a product, or dataset defined according to a format specification and a data model. Users of feature codes are advised that, as with any dictionary, there may be more than one way to encode geographic entities, either by offering a choice of features or a combination of features and attributes. A heliport is listed as feature GB035 Heliport, but could also be encoded as feature code GB006 Airfield associated with the attribute APT Airfield type containing a coded value of 009 Heliport. Another example would be AK090 Fairgrounds and AK091 Exhibition Grounds, which could be interchanged depending on the users own interpretation.

3.3.8.2 Model Name