Theory – Why Correct?
There are two reasons why you might want to correct textures in a SketchUp model that you plan on exporting to Virtualwind:
- Visual Accuracy
- Geometric Accuracy
Visual Accuracy
The current version of Virtualwind only supports faces that are textured on the "front" side; any texture on the "back" side will be ignored. If you are technically oriented, the "front" a Face is the side that the normal vector sticks out of, according to the right-hand rule. If it is important for your model to appear similarly in Virtualwind as it does in SketchUp, you will want to run Texture Validation on your model &ndash although you should note that you will never be able to export two-sided texturing without tweaking the geometry. If visual accuracy is not very important, then you can skip texture validating – however read the section on Geometric Accuracy before making your decision.
Geometric Accuracy
When simulating windflows around Canopies, Virtualwind distinguishes between the "front" and "back" sides of a face. In particular, Virtualwind assumes the front side of a given face corresponds to the "outside" of the Canopy, and the back side of the face corresponds to the "inside". For Canopies that are truly "sheet-like" – for example, an open fence – the concepts of "inside" and "outside" have little meaning, so it doesn't matter which way the face is oriented. However, for Canopies that represent closed structures, for example, a building that was too difficult to convert into a Solid, there is a well-defined notion of the "inside" surface and the "outside" surface. In these cases, having the wrong orientation can have a slight impact on the accuracy of your simulation.
Having said this, it is important to point out that, although this effect is real it is a small effect. In many cases, the reversed-face effect will be dominated by other factors. For example, if you intent to run a course-grid simulation (e.g. 32-cubed), the inaccuracies introduced by running on an unrefined grid will far outweigh reversed-face inaccuracies. Indeed, if the intended use of your Virtualwind simulation is so sensitive that reversed-face inaccuracies are troublesome, you might want to consider modelling your geometry as a Solid instead of a Canopy. Virtualwind handles Buildings with generally more accuracy than Canopies.
At this point, you might be thinking, "Thanks for the tip – but what does this have to do with textures?" It turns out that Textures can sometimes provide clues that a face might be reversed. In particular, it turns out that "back-textured faces" – that is, faces that have textures only on their "back" side, but not on the "front" side – are often an indication of a reversed face. This is handy, because by flipping back-textured faces, you can often correct a lot of reversed faces. You will note in the following sections that the Virtualwind SketchUp Plugin provides tools for detecting and even correcting problematic textures.