Architectural_Design_with_SketchUp

Chapter 5 Rendering in SketchUp
This has various implications for rendering. First of all, many 3D modeling
and rendering programs display only the front side of faces—the
back side is often simply not displayed. In addition, SketchUp has the
ability to assign two different materials to the same face—one to the
front and one to the back. This is also not always supported by other
software.
While many exporter plugins and integrated rendering software
deal with this internally (where you don’t have to think about it), it is
important to know about this in case you need to troubleshoot. In any
case, the best rule is to always have fronts of faces point outward (or
toward the camera).
Fortunately, SketchUp has a built-in function that flips a face’s orientation. To use it, select
the faces you need to flip and then right-click on one of them. Select Reverse Faces from the
context menu, and you will see the face color change. If you already have materials applied
to those faces, switch the Face Style to Monochrome (in the View menu) beforehand. This
suppresses all textures and lets you find reversed faces by showing you default face colors.
If you need to export a SketchUp model to use in any other 3D modeling or rendering
application, look at the exporter options. Some of the options, accessible through the File k
Export k 3D Model. . . menu item, allow for transfer of two-sided faces. (See Figure 5.26.)
Figure 5.26: Option in the DAE export
dialog to use two-sided faces
Triangulation
Unlike many other 3D modeling software packages, SketchUp has the ability to use polygonal
faces that have more than three edge points (or vertices). This allows us to use rectangular faces
for walls—or even hexagonal faces (as shown in an earlier example).
While this is very useful for texturing—SketchUp’s built-in texture positioning functions
work on single faces only, for example—3D model export and processing by rendering applications
typically leads to a triangulation of these polygonal faces.
This does not often cause problems, because the textured 3D model export into a rendering
application is handled automatically by an exporter plugin. It is important to know
this, however, for troubleshooting and for special cases.
One of these cases occurs when you use faces with a light-emitting material (e.g., to
simulate a “light box” or a neon tube). While this can make a very nice-looking, diffuse light,
it is important to keep in mind that the geometry of the faces that have the material applied
should be as simple as possible—best is a triangle. If you use a circle with a light-emitting
material, for example, the circle will be exported into the rendering application with many
more faces than the one it has in SketchUp (see Figure 5.27 for an illustration of this). The
higher number of faces can increase rendering time significantly.
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