Google SketchUp Cookbook

Chapter 5. Roofs: Constraints and Inferences

Inferences in SketchUp are those colored dots and dashed lines, and helpful text boxes, that appear while drawing, such as On Red Axis, On Face, Midpoint, and so forth. You can use inferences to ensure that you are drawing lines in the correct direction (red, green, or blue), starting a line at the right place (on an edge, endpoint, or midpoint), or drawing an object on a face. In addition to those basic uses, inferences also can be used to constrain objects, either to another object or to a direction. Constraining means you are forcing an object to have a certain geometric characteristic, such as a direction or start point.

To master SketchUp, understanding constraints is a must. You know the basics: a red preview line means a line will be drawn parallel to the red axis, and so on. You may even be an old hand at Shift-locking, aware that pressing and holding Shift while a preview line is red keeps the line in the red direction. But have you used double constraints or tried using the arrow keys? In this chapter, you’ll learn about these and many more powerful ways constraints can help you work more accurately and effectively.

Most of the recipes involve roofs, which can pose vexing problems in building design but benefit from well-applied constraints. Even if you’re not an architect, keep reading. The techniques presented are great for a wide variety of projects, because learning how to use SketchUp’s constraints is simply essential to ...