The objective of the external choice is to assign volumes to a given number of connections according to variable user-defined rules for later re-import of the connections in Visum so that a usual assignment result will be available (User Manual: Reading connections and routes).
In the chart in Image 161 this is scheduled above the network loading. The paths contained in the connection file are converted into the internal data structure and therefore no longer differ from paths calculated within Visum. Thus, connection import has the same effect as an assignment.
This means the following:
- By default, the program deletes assignment results for demand segments to which connection import is applied.
- From the imported connections, paths are generated in Visum according to the current setting of the option Save paths (as connections / as routes / do not save) (User Manual: Settings for saving PuT assignment results).
- The procedure setting Save paths as connections includes an option that allows you to sum up the volumes of existing connections.
- At the same time the path volumes read in are transferred into network volumes.
- If the volumes of a demand segment that has been selected for the import are to be saved with another demand segment according to the current general procedure settings, then this parameter will be reset to the default (Do not save with a different demand segment).
