Geometry Creation Strategies
Now that you have a better sense of what Building, Canopy, and Terrain Entities are, and what is considered "watertight geometry" and "non-watertight geometry", the concept of making models for use with Virtualwind will be introduced. Making Terrains, then Canopies, and finally Buildings will be addressed.
Making Terrains
Terrains are often a "nice-to-have" element of a model, but not a particular necessary one. If the surrounding landscape is flat, skip making a terrain. If a flat terrain is needed or desirable for aesthetic purposes, using SketchUp's native "Rectangle" tool is completely adequate. For rougher terrains, use the tools in SketchUp's "Sandbox" plugin. It is part of the SketchUp package, however, you will need to access the Preferences window to activate it. See SketchUp's own documentation for more information on the Sandbox plugin.
Making Canopies
Making Canopy geometry is really easy: just draw something. If you do not take any precautions, you will end up with non-watertight geometry, which can only become one or more Canopies. The downside is that any Virtualwind simulation that you run using this geometry will be slightly less accurate than if you had ensured that it was watertight geometry.
It is recommended that you make judicious use of SketchUp's "Group" feature. Virtualwind's "Part" constructs are derived directly from the SketchUp Groups in your model. Although Parts do not affect the simulation characteristics, they are very useful for display purposes. Moreover, you may decide at a later date to "clean-up" certain portions of your Canopy to conform to watertight geometry rules. If the model is already divided in Groups, you will have an easier time.
Making Buildings
Making watertight geometry (and therefore valid Building geometry) is straightforward if you take an incremental approach. Here are some tips to keep in mind:
Check for watertightness often: The Virtualwind Plugin offers a wide array of watertightness-checking tools. The Separate Solids and Canopies Tool can be particularly useful to determine at a glance if any unexpected geometry has become non-watertight: use it often. When problematic geometries do occur, the Watertightness Tools will be helpful in locating and correcting the problem.
Use Groups: In addition to all the normal-usage reasons for using SketchUp's Groups and Components features, it is smart to use them when creating watertight models. Creating a model on a group-by-group basis automatically isolates problematic geometry when it does occur. Moreover, the Watertightness Tools mostly operate on the currently active Group, making it even easier to locate and resolve problems.
Save often, but only save watertight states: Despite all your best efforts, model creation can sometimes get out of hand. If non-watertight geometry creeps in unnoticed, sometimes the easiest recourse is to reload the model from an earlier state. It is therefore good to save often, but only save if you know that your watertight geometry has not been corrupted. Use the Separate Solids and Sheets Tool before saving.
Familiarize yourself with SketchUp: SketchUp has a few features that are helpful when creating general-purposes models, but can sometimes have adverse effects when trying to create watertight geometry. For example, SketchUp will automatically create a face when it detects a co-planar edge cycle. This, and other features, can be a boon in some situations and a bane in others. If you are familiar with SketchUp you can anticipate problems before they happen – or at least be less surprised when "unexpected" geometry does appear.