Opus is a new platform for urban and regional simulation, designed to support the development and integration of model components for simulating the effects of major transportation investments and policy changes on transportation, land use, and the environment. Opus consists of a collection of packages written in the Python language. The choice of Python was based on Python's balance of characteristics, which provide a good combination of a productive development (even for users who are not expert programmers), and good performance due to the availability of Python libraries for fast numeric processing that use C or C++ to implement computationally intensive aspects. The basic functionality of Opus is implemented in a package named opus_core.
UrbanSim Version 4 is implemented as a set of Opus packages. (Previous versions were in Java.) The decision to migrate from Java to Python was based on the faster development and computation time available in the Python environment with numeric libraries, and on the objective of making models in UrbanSim more modular than they had been in the previous Java version, allowing users to rapidly configure models, estimate their parameters, and use them. In addition, Python is turning out to be a more accessible language for modelers, which addresses another key goal: to create a system where modelers can write their own models, and understand the models written by other modelers.
This document covers both the base set of Opus packages and the UrbanSim system implemented in a set of Opus packages. As descriptions become available, other packages besides those related to UrbanSim will be added. We expect that over time many users and developers will contribute packages to the system, making their work available to others in the same way that they themselves have benefited from others' work.
The document includes both a user guide and reference manual. Part I is currently just this introduction and a technical overview of the UrbanSim model system, but will soon also include a technical overview of Opus. Part II describes how to install and use Opus and UrbanSim. Part III contains reference material on the details of Opus and UrbanSim. Part IV provides information for software developers (i.e., people who will be writing new Opus packages or documentation). A short Glossary is provided in an appendix.
This document will continue to evolve -- questions and open issues are in italics. Please feel free to send your comments, criticisms, and suggestions to info(at)urbansim.org. The latest version (as a pdf file, and as html pages) is linked from http://www.urbansim.org/.