Link orientations play an essential role when defining node geometries (Geometries). The link orientations are used to determine the amount of legs. Each link has at least four orientation attributes: From and To node orientation, and From and To main node orientation. The two latter attributes are only defined for cordon links of a main node (Main nodes and main turns). The orientations are always undefined for closed links. A link is closed if its transport system set is empty or if the number of lanes is zero. If a link is not closed, it is an open link.
Up to sixteen link orientations can be defined at a node or main node. If a node or main node has more than sixteen open incoming links or more than sixteen open outgoing links, all link orientations will be undefined. At such nodes, no geometry and thus no signalization can be defined.
The allocation of link orientations complies with specific rules. If an incoming link and its opposite outgoing link are open, the To (Main) Node Orientation of the incoming link and the From (Main) Node Orientation of the outgoing link are identical. If there is an incoming link whose opposite direction is closed, you can allocate the same orientation to an outgoing link, as long as its opposite incoming link is also closed. You can also combine incoming one-way roads and outgoing one-way roads in one leg (Geometries) if you give them the same orientation.
Whether Visum calculates the link orientations automatically at a node or main node or not, depends on the attribute Use automatic link orientation. If the link orientations are calculated automatically, the type of calculation depends on the option set under Network > Network parameters > Network objects > Link orientations (Using Visum: Specifying the number of link orientations). Normally, the value is set to 8. This means that Visum picks the best orientations from the four main directions (N, E, S, W) and the four secondary orientations (NE, SE, SW, NW). The entry angle of the link at the node or main node is decisive when selecting the orientation. If the orientations do not suffice – i.e. the node or main node has more than eight legs – Visum adds the subordinated secondary orientations (e.g. NNE).
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Note: Please note that you can define varying numbers of legs at a node or main node, depending on the number of pairs of incoming and outgoing one-way roads that are given the same orientation. |
