You can set up user-defined VD functions for the following use cases:
- To include further attributes for links, turns and connectors in the calculation
- To calculate PCUs in a non-standard way
- To define separate volume-delay functions for different transport systems
Volume-delay functions are very often evaluated within the assignment methods, so computational efficiency is a key consideration. Therefore Visum adopts a compiled rather than an interpreted approach to user-defined volume-delay functions. Users program their functional forms as a dynamic-link library (DLL) following a given template. Then copy all *.dll files created to the following project directory, which by default is created during the installation process in the User Data folder of the Windows user. It is scanned by Visum at start-up: ..\AppData\Roaming\PTV Vision\PTV Visum 2021\UserVDF-DLLs (User Manual: Applying user-defined volume-delay functions).
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Note: A *.bmp file with identical file name which is stored in the same folder will be displayed for VDF selection. |
