Special FME feature attributes are used to hold GDF information. The GDF writer will use these attribute values as it fills in GDF records during output. The GDF reader will set these attributes in the FME feature it creates for each feature it reads.
The GDF writer uses the FME feature type attribute to correctly write each feature, and will ignore those that do not correspond to GDF primitive record types. The feature type will be set by the reader to either the value without the gdf_ prefix (and GDF record type in uppercase), or a geometry type in lowercase, such as gdf_level_1_point.
| Attribute Name | Contents |
|---|---|
|
gdf_type |
The FME name for the type of element this feature represents. Range: See the table in the Overview section. Default: No default |
The topics below describe parameters specific to each of the supported feature types:
- level_0_point
- level_0_line
- level_0_polygon
- level_1_point
- level_1_line
- level_1_polygon
- level_2_point
- level_2_line
- level_2_polygon
Level 1 and Level 2 features may also contain attributes from the GDF specification as well as user-defined attributes.
For example, if a user-defined postal code attribute is included, the following attributes will be present on the feature:
- “Custom Postal Code” - holds the actual value of this attribute
- “Custom Postal Code_ABS_REL” - indicates whether absolute or relative curvimetric positions are stored.
- “Custom Postal Code_ATT_DIR” - holds the direction(s) for which this attribute is valid.
For example, if a standard GDF attribute such as “official name” (ON) is included, the following attributes will be present on the feature:
- “Official Name” - holds the actual value of this attribute.
- “Official Name_ABS_REL” - indicates whether absolute or relative curvimetric positions are stored.
- “Official Name_ATT_DIR” - holds the direction(s) for which this attribute is valid.
- “Official Name_DESCRIPTION_ID” - Source Description Identifier ID. Number of a source document for the attribute.
- “Official Name_LANGUAGE” - The MARC language of the specified name.
- “Official Name_NAME_DESCRIPTION_ID” - Source Description Identifier ID. Number of a source document for the name.
Some attributes are actually composite attributes, meaning they are groups of values that together have a particular meaning. At this point, this representation of composites is handled only by the GDF reader. For example, Direction of Traffic Flow may have different restrictions for bicycles than they do for passenger vehicles. These composite attributes will be represented as follows:
- “Composite Direction of Traffic Flow” - {{Direction of Traffic Flow=4}{Vehicle Type=10}}
The outer bracket pair shows that the contained values refer to each other and the inner brackets mark each particular value. In some cases, a composite may contain other composites. In certain instances, it may be inconvenient to deal with such a structure, but composites are also represented on a feature in a list format as follows:
- “Composite Direction of Traffic Flow{0}.Direction of Traffic Flow” = 4
- “Composite Direction of Traffic Flow{0}.Vehicle Type” = 10
Note: In the case of composite attributes, the ABS_REL and ATT_DIR will only appear on the top level (that is, they won’t be included for subattributes).
All the standard GDF attributes as well as user-defined attributes are concatenated together as a single string provided in an attribute gdf_all_attributes. The attribute names are followed by their values in this string.
All features will have the following attributes: gdf_volume_id, gdf_dataset_id, gdf_section_id, and gdf_layer_id where applicable. These values are taken from the header of the corresponding record and attached to the feature. A feature will only have these IDs for its level and those levels that are higher, provided that the ID value is specified.