Network data import
The network data import is used to exchange data with external sources. Thus, on the one hand, you can integrate information into a transport model and, on the other hand, transfer results from a transport model to an external network.
Use cases
- Enriching the transport model with information from other data sources (e.g., road databases) regarding:
- Construction sites
- Road works planning
- Future planning
- Road condition
- Transfer of transport system-related information, e.g. bicycle routes
- Update of link attributes
- Transfer of volumes from a transport model to external data sources, such as road databases, for use or display in other systems
Prerequisites
- Transfer of external data into a Visum version file, e.g. by importing shape files.
- Both version files must be georeferenced.
- Route capability in the external network is an advantage, but not mandatory.
Import procedure
When importing, you typically have the transport model open in Visum - referred to below as the 'currently loaded network' - and load the version file with the external data - referred to below as the 'external network' - in the background.
In the first step, link sequences are generated in the external network for each imported transport system, i.e. a set of connected links that are permitted for this transport system including the in-between turns and are similar with regard to selected link attributes.
In the second step, the link sequences are mapped to links of the currently loaded network. This step is done using the shortest path search and Map Matching. The procedure is as follows:
- By looking at them in isolation, a set of possible locations ("candidates") in the currently loaded network are assigned to the nodes or link course points of the link sequences in the external network. When selecting candidates, the parameters Snap radius for geographic candidate search and Maximum number of candidates per link course point are relevant. If you have allowed the insertion of nodes and links in the import settings, the transformed positions of nodes or link points are also inserted as candidates in the candidate set.
- Based on the candidates of all positions of a link sequence, a node-edge graph is formed internally, i.e. a shortest path search is performed in the currently loaded network for candidates of consecutive candidate points. If this shortest path search is successful, the edge is inserted into the graph and receives a score. The evaluation takes into account:
- The position of the candidate in relation to the position in the external network
- The cost of the shortest path search
You define the weights that are included in the evaluation in the import parameters. The path in the graph with the best rating is assigned to the link sequence.
The third step is the transfer of attribute values. The transfer of attribute values can be done in both directions. In the following, the version file from which the attributes are transferred is referred to as the source network, and the version file to which the attribute values are transferred is referred to as the target network. If the currently loaded network is the target network, optional network changes can be made, i.e. Links and turns can be opened, nodes and links can be inserted or existing links can be split. According to the allowed network changes in the currently loaded network, the transport system relevant for the link sequence is transferred from the external network - according to the allocation to transport systems in the currently loaded network - i.e. links and (main) turns are opened or links and nodes are inserted. Network changes are not allowed if the external network is the target network. The attribute values are transferred using an allocation of the target link to a list of source links and their overlap length. According to the type of attribute to be transferred, aggregation functions and other parameters can be selected.
Note: Both transfer directions have their application. When you transfer results, such as volumes, from a transport model to external data sources, you typically do not want to change the network data from external sources. However, in order for all data to be transferred, the external data must be the basis for generating the link sequences, i.e. it must act as an external network, and the data from the currently loaded network must be transferred to the external network. |
Recommended procedure:
1. Import external network data to Visum, e.g. by importing shape files.
2. When importing, select this version file as External network.
3. Make the desired settings for the import (Importing network data)
4. Review and analyze network changes identified in the model transfer file generated following the import. You can also check the generated link sequences when importing them into POIs of a selected POI category in the currently loaded network.