Aggregating isolated nodes

Note: You can only execute this operation if there are isolated nodes in the network, for example when reading external network data additively (Reading network data additively).

The aim is to automatically integrate isolated nodes into an existing network. You can insert isolated nodes as stop points in the network, even if no stop points were assigned to the nodes before. This facilitates the integration of stop data into an existing private transport network model.

The integration sequence is based on the distances between the isolated nodes in the network. The process begins with the node that is located closest to the basic network. If required, the distances are determined anew after each integration step. Then, the next closest isolated node is integrated and so on.

It ends when all isolated nodes have been integrated or when the network lies beyond the snap radius of all remaining isolated nodes. For stop points, the minimum distance between neighboring stop points on links is regarded. Below the minimum distance, a node carrying a stop point is inserted.

It is ruled out that two initially isolated nodes are merged in the process, as data would be lost otherwise. This situation could occur if the first node, after it has been integrated, turns into the network object nearest to the second one. The second node would not be merged with the first one then, but would either remain isolated or be integrated into the network in a different way, using the following trick. This trick only works if the first integrated node has one or two legs following integration. In this case, an incident link of the node is split and the second isolated node is used as an intermediate point.

The isolated nodes retain their attributes in any case – even if merged with network nodes which would then lose all their attributes instead.

Note: The coordinates are an exception to this. You can specify whether the coordinates of the existing network or the coordinates of the isolated nodes shall be used.

1.  Select the nodes, which you want to integrate, via

• the spatial selection (Setting network objects active/passive via the spatial selection) and/or
• filter criteria (Using filters to set network objects active or passive).

2.  In the Network window, right-click the Nodes button.

A shortcut menu opens.

3.  Select the Aggregate isolated nodes entry.

The Aggregate isolated nodes window opens.

4.  Make the desired changes.

Scope Nodes to be integrated (source)
Element	Description
Integrate only active nodes	If the option has been selected, only active isolated nodes are integrated into the network. If the option has not been selected, all isolated nodes are integrated into the network. Note The active/passive attribute is not relevant to existing network nodes.
Snap radius	The snap radius determines the area surrounding an isolated node, within which network objects will be searched. If neither network nodes nor links are located within this area, the node in question remains isolated. As with link lengths, the snap radius takes the scale of the network into account. The default value is 100.
Tolerance range for merging	If there are any nodes within the tolerance range that are contained in the snap radius (default=5m), the node to be integrated will be merged with the nearest node within reach. This is done, even if a link is positioned closer to that node.

 

Scope Integration parameters
Element	Description
Use coordinates of	Use this option to specify whether the coordinates of the isolated nodes or of the existing network nodes shall be used. Nodes and links of the network If this option has been selected, the isolated nodes slide into the network. Isolated nodes If this option has been selected, nodes and links (intermediate points) move towards the initially isolated nodes. In this case, a few things should be noted: Due to the gradual changes to the network topology, it can happen that a different network object is allocated to the isolated nodes that have not yet been integrated (which, as a result, changes their distance to the existing network) than at the start. This can result in the existing network "going beyond" the snap radius of an isolated node, or that it "moves into" the snap radius not until the course of the procedure. The basis for each subsequent step in the integration process is always the shortest distance of the isolated nodes to the network that is currently valid. Adjust link lengths to direct distances If the option has not been selected, the link lengths are not recalculated.
Use stop allocation of	Allocations of stop points to stop areas should remain untouched by the integration of isolated nodes. If two stop points are merged however, their aggregate can refer to only one of the previously allocated stop areas. Use the options to specify which stop area shall be used. Nodes of the network Default setting Isolated nodes You can delete stop areas and stop points which are separated from the network as a result of this operation. You can, for example, filter isolated objects via the attributes CStopArea::NumStopPoints and CStop::NumStopAreas and delete them via Multi-delete.

 

Scope Network integration (target)
Element	Description
Integrate nodes:	As existing If this option has been selected, isolated nodes are inserted with an assigned stop point only if they carried a stop point before the integration. Always as node with stop point (default setting) If this option has been selected, isolated nodes are always inserted with a stop point. The link is split and the isolated node inserted where the link is split. Note The Permit creating on links must be selected. Always just as stop point If this option has been selected, the isolated node is inserted as a stop point which is placed either on a network node or on a network link. Links are not split however. Note If the Permit creating on links option has been selected, undirected link stop points might be inserted.
Permit creating on links	If this option has not been selected, the network integration is performed exclusively by merging nodes. This ensures that, when determining the next network object, only nodes are considered. Usually, more isolated nodes remain as a result. If this option has been selected, stop points are created; the link without the link being split. Stop points created in this way are undirected and therefore serve both directions of the link. If a node is merged with an already existing directed stop point, the stop point will be undirected after the aggregation.
Create only on active network links	If this option has been selected, objects will be inserted on active links only. Passive links are ignored.
Merge only active network nodes	If this option has been selected, isolated nodes will only be merged with active network nodes. Passive network nodes are ignored.
Permit merging with stop points	If this option has been selected, an isolated node can be merged with a stop point which already exists in the network, as long as it lies within the user-defined snap radius and the tolerance range. If this option has not been selected, an isolated node cannot be merged with an already existing stop point. This might make sense if you want to import a large number of nodes as stop points, because it is usually undesirable to merge an existing stop point with another object that has just been inserted. The new node remains isolated and needs to be handled separately, where applicable. Exception Since the Aggregate isolated nodes procedure prevents that two initially isolated nodes are merged, just one node will be integrated into the network, if any, if the option has not been selected. Further nodes remain isolated or split an incident link, if possible. Note The log file (Using protocol files) also contains failed integrations. If integration fails because it is not allowed to merge nodes with stop points, a corresponding entry with the operation number "4" is added.

 

Note: In large networks, select option Temporarily deactivate command history to save storage space, if required. No commands will then be saved during the aggregation.

5.  Confirm with OK.

Notes on the integration logic

During the integration, the attributes (especially IDs) of the isolated nodes (and their stop points) are always transferred to the network. Only for co-ordinates and the stop hierarchy, there are special choice options. If a stop point is generated from a node, the code and the name of the stop point is the same as the code and the name of the node. However, if two stop points are merged, no transport system will be blocked that was permitted to use the stop point in the network before.

The objects contained in the network are only overwritten despite transferring the data, rather than being deleted in terms of the object identity; in other words, dependent data (for example line routes that use stop points) are not lost.

Stops and stop areas which exist at isolated nodes, might also be isolated after the integration process, yet are not deleted automatically. Their coordinates are never adjusted.

Case 1: Merging isolated nodes with network nodes

Note: The minimum distance of an isolated node to the network determines which of the following cases results.

Merging an isolated node with a network node leads to one of four scenarios, as both, the isolated node and the network node, can but do not necessarily carry a stop point. The Use coordinates of option clearly determines, which network object "wins". The transport system set of an existing stop point is never reduced.

Case 2: Creating on link courses

If the Permit creating on links option has been selected and a point on a link polygon, which is neither the From-node nor the To-node of the link, is the network point located nearest to the node, the isolated node will be inserted on the link course.

The link is either split and a new node (possibly with stop point) is inserted, or a stop point is placed on the link.

Please note: Since there is an internal minimum distance (= link length/1000) between adjacent stop points on a link, the insertion of a stop point might fail if the value falls below the limiting value. In this case, a node with a stop point on the link is created, even if option Always just as stop point has been selected. This is possible as there is no internal minimum distance between stop points and link nodes.

Case 3: Merging with link stop point

In rare cases, a stop point on a link might be the network point located nearest to the isolated node. This is a combination of case 1 and case 2: a merge operation according to case 1 is performed on a link as in case 2, which is then split (only if a node shall be inserted). As in case 1, the transport system set of existing stop points is not reduced. The minimum distance problem cannot occur in this context.

Note: You will find detailed information on the procedure in the message window.