CityEngine does a great job at generating street networks, but how do we model the places where streets already exist? Drawing geometry over an aerial view may suit a very small project. What about entire neighborhoods or corridors? The answer is we need files containing street “centerlines”, and the word means exactly what it says. The lines (edges) in these files run right down the middle of each street so you can vary widths as needed without losing basic roadway alignments.
CityEngine can handle four street centerline file types:
- Drawing eXchange Format (DXF)
- OpenStreetMap (OSM)
- Shapefiles (SHP), developed by ESRI to store vector data
- File Geodatabases (GDB), where collections of data are stored for ArcGIS
DXF – Autodesk, Inc. is the producer of AutoCAD, an established Computer Assisted Design application used in the Architecture-Engineering-Design world. According to the Autodesk Knowledge Network, “A DXF (drawing interchange format) file is either a binary or an ASCII representation of a drawing file. It is often used to share drawing data between other CAD programs.”
OpenStreetMap (OSM) is a worldwide, open-data street map maintained by “a community of mappers”. Data can be used at no cost as long “as long as you credit OpenStreetMap and its contributors”. Getting an OSM file of a specific area is simple:
- Go to the OpenStreetMap web site, www.openstreetmap.org
- Pan and Zoom the map so the area you need is entirely within the browser window — or click “Manually select a different area” in the upper left and draw a box around what you need
- Click EXPORT at the top of the page; a file will download
- Move the OSM file to your CityEngine project folder
I called up and downloaded an OSM file of my old suburban Chicago neighborhood in less than a minute m(Figure 2).
SHAPEFILES – of course, there are some great data sets out there on the Web if you know where to look. I downloaded all of the street centerlines for the City of Chicago, and building footprints (802,606 of them) to boot via the City of Chicago Data Portal (Figure 3). With all of that geometry, if I want to work with a certain area in CityEngine or ArcGIS, I must clip out the area I need.
GEODATABASES will likely contain a number of different layers — like centerlines and building footprints — that you can use when needed.
Importing a centerline file into CityEngine is as easy as dragging it from the Navigator window into the Viewport. You should see a street network (graph) with nodes and edges. There may be a pop-up that asks you things like what layers you want to import, whether you want to run graph cleanup, what your snapping tolerances are, etc.
As you may be modeling changes to existing conditions, having accurate, geographically correct street centerline data is hugely important, particularly where tolerances may be crucial. Having related data like building footprints that fit right in to your street network, is a huge time saver too!