TRANSCAD教程2：The Miasma Beach Transportation Model

  ch direction is AB and which is BA, you need to know the direction in which transcad draws this link. Look at the following example.

Link 25 contains two end nodes, Node 310 and 320. If this link is drawn from 310 to 320, then Arrow 1 is AB and Arrow 2 is BA.

               Node 310 +------------------+ Node 320

                             Link 25

               Arrow 1  ------------------->



               Arrow 2  <-------------------

The direction a GIS draws a link is referred to as the topological direction of this link. This information exists internally in the database (e.g., somewhere in the MB2001 files). If you want to see a link's topological direction in Dataview, set Highways/Streets as the working layer and go to Dataview / Formulate Fields. On the Formula (Dataview: Highways / Streets) dialog box, click at the Node Fields button. Another dialog box Node Formula Fields come up. Highlight ID under Choose one or more node fields and select "From" and "To" under Option. Click OK. You should see two fields, [From ID] and [To ID] being add to the dataview. [From ID] is ID of the node from which the link begins and [To ID] is ID of the ending node.

Exercises:

• How do you designate a link as a one way street? (Hint: 1 or -1 in Dir)

To calculate the free flow speed for all the streets in the Miasma network, first go to Dataview / Modify Table. Click on Add Field button. Enter the followings under Field Information:

1. Name: AB_TRAVEL_TIME
2. Type: Real Number
3. Width: 10
4. Decimals: 2

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