Network optimisation
- OD-connection-road = the link from/to an origin/destination point. Result of a connect operator.
- NodeSet = set of nodes in the network. This is unchanged from the beginning to the end of the script
- LinkSet = set of links between nodes in the network. This is repeatedly created in each iteration
- JunctionFreeSection = a set of links that together form a link without junctions.
In this image, nodes 1, 2 and 4 to 8 are regular nodes in the network. Nodes 3 and 9 are OD points. Links a and c to g are regular links, and b and h are OD-links.
We use iterations, where Iter0 starts with the LinkSet_src from the CreateInitialLinkSet. In later iterations, we start with the IntermediateLinkSet from the previous iteration.
The unique locations are constant over the iterations. However, the LinkSet is not constant across iterations, so we need a new Link_rel in the location set. In the NodeSet, which is the same domain as the NodeSet_src and thus constant over the iterations, we define the nodes that can be deleted.
The first step is to identify the nodes that can be deleted because they are not junctions (i.e., the number of connecting links equals 2) and are not part of an OD-connection link. If a node is used in the link between an OD point and the network, it is considered an OD-connection-road-node.
In this case, junctions 6 and 7 have only 2 connecting roads and are not OD-connecting points. Therefore, they are earmarked as WillBeDeleted.
Then, we use the NodeSet/WillBeDeleted to identify which links in the LinkSet are part of the JunctionFreeSection.
- IsPartOfJunctionFreeSection is defined as the F1 OR the F2 WillBeDeleted.
- IsInsideJunctionFreeSection is defined as the F1 AND the F2 WillBeDeleted.
- IsOnBorderOfJunctionFreeSection is defined as IsPartOfJunctionFreeSection AND NOT IsInsideJunctionFreeSection.
- IsFinalLink = UnchangedLink, which are those links that will not change.
In this case, links e, f, and g are IsPartOfJunctionFreeSection. Meanwhile, link f is the only one earmarked as IsInsideJunctionFreeSection. Furthermore, links e and g are IsOnBorderOfJunctionFreeSection.
This is a subset of all links inside the JFS, as defined in the NodeSet. In our case, only link f is included. We check these links using the connected_parts-operator, which links are together one JFS.
This set comprises all the links on the edges of the JFS, in this case, links e and g. Here, we see which node will be deleted or connected to the unchanged link.
From the connected parts in LinksInsideJunctionFreeSection, we derive the distinct JunctionFreeSections. Here, we find the Connectorlinks on either side of the JFS and collect the relevant attributes from those links (e.g., impedance and length). Furthermore, we create new F1 and F2 of the endpoints for the two connector links. In our example, from link e, node 4 is the endpoint, and from link g, node 8 is the endpoint.
We now aggregate the collected attribute values from the connector links with the links inside the JFS. We have a new link, a straight line with all the attributes correctly aggregated. In our example, it is a link from node 4 to node 8.
Now, we combine the unchanged links with the new straight-line JFS.
At this point, we check for dead ends. If this domain's F1 and F2 only occur once in the NodeSet and it is not an OD-point, we earmark the link as ToBeOmitted. In the example, nodes 1 and 4 are used.
- We also check if a link is connected with itself if
F1 == F2. - And lastly, we check and remove duplicates when collapsed, and . N.B., at the moment, regardless of its direction.
From the LinkSet_cleanedForJFS, we omit all the links that are dead ends, duplicates, or connected with themselves.
Again, look for JunctionFreeSections and simplify them. Clean and look for dead ends, duplicates and connections with itself.
Continue until no further cleaning is required.
From the original 9 nodes, only 4 remain.