Importing Geometry
The first step of conducting a Virtualwind study is to set up the environment within which the wind is simulated and visualized. The environment, which may feature an urban, suburban or rural area, typically encloses structures such as buildings, canopies, and terrain. In Virtualwind, the models of these structures are referred to as geometry. Geometry can be constructed in 3D design packages or captured from 3D digital sensing systems.
When importing the geometry, Virtualwind needs to know whether it is a Building, Canopy, or Terrain.Virtualwind provides two different paths to import geometry:
- Build the geometry in Google SketchUp and export to Virtualwind by using the tools of Virtualwind SketchUp plugin.
- Convert the geometry into a STL file (Stereolithography file format, usually with an extension .stl) and import to Virtualwind by using the importing tools of Virtualwind.
Importing Geometry Created in Google SketchUp
Using Virtualwind SketchUp plugin tools, you can directly construct geometry that meets Virtualwind requirements – the geometry is well-formed and readily classified to Building, Canopy, and Terrain.
Another benefit of constructing geometry in SketchUp is that you can choose to retain the texture information from SketchUp models when exporting to Virtualwind (whereas taking the second path, i.e., via the STL file format, will lose all the texture information).
Importing Geometry in STL format
Virtualwind also provides tools to import geometry in the STL file format, both ASCII and binary. However, since the STL file format does not convey the classification information, you have to tell Virtualwind whether you want to import the geometry as buildings and canopies, or terrain.
Note that STL files do not store the unit information used for the models and Virtualwind assumes that they are expressed in meters. So when converting models to a STL file, you have to make sure that they are in the right unit, otherwise you will find that they are wrongly scaled when imported into Virtualwind.
Importing Geometry as Buildings and Canopies
The tool, located at File → Import → Import Buildings And Canopies, automatically separates the models if multiple models are contained in the STL file. Then it examines the Watertightness of each model and classifies it as Building if it is watertight or Canopy if not.
Importing Geometry as Terrain
Virtualwind assumes that the imported terrain is an open surface (a sheet) and the projection of its boundary on the ground is a simple polygon (or simple polygons that do not intersect with each other) – the projection of the boundary does not have self-intersection.
The tool, located at File → Import → Import Terrain, checks the above condition and pops up a message (and aborts the importing process) if it is not satisfied.