Class Name: Edge Direction

Superclass - <SEDRIS Abstract Base>

Subclasses

Definition

An instance of this DRM class indicates, for the associated relationship, whether the target edge should be traversed forwards (from start node to end node) or backwards (in the opposite direction).

Primary Page in DRM Diagram:

• 23

Secondary Pages in DRM Diagram:

• 8
• 11

Example

1. A <Linear Feature> instance representing a stream is associated with several <Feature Edge> instances that define the path of the stream. The <Edge Direction> associated with each <Feature Edge> has forwards = SE_TRUE if the <Feature Edge> is oriented so that the stream flows in the direction from its starting node to its ending node, and SE_FALSE if the stream flows in the opposite direction.

2. Consider a <Linear Feature> instance representing a one-way street. Its path is defined by a <Feature Edge>, so that the <Edge Direction> between the <Linear Feature> and the <Feature Edge> indicates whether the orientation of the <Feature Edge> matches the permitted direction of travel along the one-way street.

3. The <External Feature Face Ring> of a <Regular Feature Face> consists of three <Feature Edge> instances. In traversing the ring, the first <Feature Edge> might be traversed from starting node to ending node, so that its <Edge Direction> has forwards = SE_TRUE If the next <Feature Edge> was traversed from its ending node (which in this example is the same <Feature Node> as the ending node of the previous <Feature Edge>) to its starting node, its <Edge Direction> would have forwards = SE_FALSE (i.e., backward).

FAQs

What if the object associated with the edge represents a spatially located entity, such such as a tree line, that has no well-defined orientation?

In such cases, the <Edge Direction>'s forwards field shall be set to SE_FALSE.

Isn't this information redundant, in the case of ring edges?

While this information can be derived by comparing the starting and ending nodes of consecutive edges within the face ring, it is provided as a convenience and as a validity check.

Constraints

Inherited Field Elements

Field Elements

Notes

Fields Notes

forwards

 If this value is SE_TRUE, the edge is oriented in the same direction
 as the object with which it is associated, so that it should be
 traversed from its starting node to its ending node.

 If this value is SE_FALSE, either the orientation of the edge is
 the opposite of that of the associated object, or the associated
 object has no clearly defined orientation. In this case, the edge
 should be traversed from ending node to starting node.