may be travel
LED in two directions, each attribute of the arc is represented by a from-to attribute and a to-from attribute. The first six fields of this table are standard and contain internal information. They are created by ArcInfo when building the arc-node topology. The EMME2-ID field is used to store a unique arc identifier number in order to maintain the correspondence between an arc in ArcInfo and a link in EMME/2. If the EMME/2 coverage is derived from an existing user coverage in the master GIS, then this number is already present and can be directly exported to an extra attribute in the EMME/2 data bank. However, if the EMME/2 coverage is derived from an EMME/2 network, this identifier must be evaluated in EMME/2. Since a two-way street, represented by two links in EMME/2, is represented by only one arc in ArcInfo, one needs to compute the identifier based on the internal link index of the EMME/2 data bank, and keep the result in an extra attribute (by default @arcid). The
EMME2-ID is computed as follows:
- the link table is scanned in ascending internal index number, and all links are assigned an index number;
- for all two-way links, the first link encountered will be assigned a positive identification value while the reverse link (the link in opposite direction) will be assigned zero minus this same value.
This is easily done with an EMME/2 macro. This distinction is required in order to establish which information is related to the from-to direction and which to the to-from direction. The table definition of
EMME2.AAT can be found in Appendix A.
The EMME2.NAT table stores information related to nodes. The first two fields of this table con
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