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AECbytes Tips and Tricks Issue #34 (September 25, 2008)

Using the Intersect Tool in Google SketchUp

Bonnie Roskes
Independent Writer and Consultant

Most SketchUp users are familiar with the Intersect tool, but many don’t know how to use all of the tool’s options. This tutorial will explain the various ways you can use Intersect.

The first example will demonstrate Intersect Selected. We’ll start with a building like this, with exterior walls in a stone material and blue interior walls.

We want windows and doors cut into the exterior walls. The easiest way to do this is to make cutting shapes (in yellow below), and combine all of the shapes into a group.

Select everything, and right-click on any selected object. From the popup menu, choose Intersect > Intersect with Model.

This creates intersection edges where any selected object meets any other object in the entire model. This means that intersection edges are created on both the exterior and interior walls. You can see this clearly if you hide the cutting group (right-click on it and choose Hide).

Undo, and this time select only what you want to intersect. (If your interior and exterior walls have different materials, you can select just the exterior faces by right-clicking on any exterior wall and choosing Select > All with same material.) With just the exterior walls and the cutting group selected, right-click and choose Intersect > Intersect Selected.

When the group is hidden, you can see the intersection edges only on the exterior walls.

To finish the doors and windows, bring back the group and Explode it. Then you can trim away the portions you don’t need.


Now let’s look at Intersect with Context. The “context” refers to the contents of a group or component. We’ll use this model—a board with pegs that could be used for hanging coats or hats. Each peg is a component consisting of a cylinder and sphere.

Open one of the pegs for editing. (To hide everything else while editing, open the Model Info to the Components page and check the Hide boxes.) Select the whole component and run Intersect with Model.

The result is intersection edges between the sphere and cylinder (shown by the yellow arrow), as well as edges where the peg meets the board (shown by the red arrow). Intersect with Model includes the entire model in the calculation, even for objects that are not displayed.

Undo, and this time choose Intersect with Context.

This time only objects within the component are included in the calculation. So only edges between the sphere and cylinder are created, and the rest of the peg remains intact. (Of course, you would get the same result if the peg were a group and not a component.).

To cut holes in the board, run Intersect with Model on it. When you hide the pegs, you can complete the holes.


About the Author

Bonnie Roskes is the author of Google SketchUp 6: Basic and Advanced Exercises, which is her fifth release on SketchUp. Books on Version 7 will be released soon, including one for O’Reilly Media. She has also released a series of SketchUp design project books and geometry project books for kids in K-12, along with some free resources for teachers and parents. Info on these can be found at www.3dvinci.net.

Bonnie has also authored books on Piranesi and OneCNC, as well as reference manuals, user guides, and tutorials for other CAD applications. She has a BS and MS in structural engineering, and worked for several years in bridge design and analysis before moving to tech writing.

Contact bonnie@3dvinci.net for info on any of her books.

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