How Do You Intersect Groups in SketchUp?

To intersect geometry residing in different groups in SketchUp, you typically utilize the "Intersect Faces" command while working within one of the groups. This command allows you to create new edges where selected faces or edges within the group meet or pass through other geometry in the model (which could be in another group or outside of any group).

One common method, as described in the reference, involves editing a group and then intersecting its faces with the rest of the model.

Using the Intersect Faces Command Within a Group

The core process involves entering the group you wish to modify and using the Intersect Faces command on the geometry inside it against the geometry outside it.

Here are the steps based on the provided reference:

1. Edit the Group: You need to be inside the group whose geometry you want to intersect. You can do this by:

   • Double-clicking on the group using the Select tool ().
   • Right-clicking on the group and choosing Edit Group.

   This action opens the group for editing, making its contents editable and dimming the rest of the model.

2. Select Geometry (Optional but Recommended): While inside the group, select the specific faces and/or edges that you want to use for the intersection. If you don't select anything, SketchUp will attempt to intersect all geometry currently being edited within the group with the model outside. Selecting specific geometry provides more control.

3. Initiate the Intersection: Right-click on a selected face (or anywhere on the geometry you are editing if nothing is selected).

4. Choose the Intersection Target: From the context menu, select Intersect Faces.

5. Specify Intersecting Geometry: Choose With Model.

   Selecting With Model tells SketchUp to look at the selected geometry inside the group you're editing and compare it against everything else visible in your SketchUp model (geometry outside this group).

Reference Information:

As noted in the reference: "Double click on the group with the Select tool or right click on it and chose Edit Group. Then right click on the face and choose Intersect FacesWith Model."

Practical Tip: The reference also correctly advises: "Best to make sure the oval is passing through the surface, not just sitting on it." This highlights that the geometry needs to overlap or pass through the target geometry for the intersection to occur effectively.

What Happens Next?

After performing the Intersect Faces > With Model command, SketchUp creates new edges wherever the geometry you were editing inside the group intersected with the geometry outside the group. These new edges appear on both the geometry inside the group and the geometry outside the group.

• Inside the Group: You will see new edges on the faces you were editing. These edges define the boundary where the intersection occurred. You can now use these edges to split faces, push/pull parts of the shape, or delete sections.
• Outside the Group: If the geometry outside the group was also raw geometry (not grouped or componentized) or if you edit the group/component it belongs to, you will also find the new intersection edges on that geometry.

This process is fundamental for operations like cutting holes through objects, trimming one shape with another, or combining complex forms that originate from different groups or components.

Example Use Case:

Imagine you have two overlapping groups:

• Group A: A rectangular prism.
• Group B: A cylinder passing through the prism.

To cut a cylindrical hole in the prism (Group A) using the cylinder (Group B), you would:

1. Double-click Group A to edit it.
2. Right-click on a face of the prism within Group A.
3. Select Intersect Faces > With Model.
4. New edges defining the cylinder's intersection will appear on the faces of the prism inside Group A.
5. Use the Eraser tool () to delete the interior faces and edges created by the intersection within Group A, leaving a hole.
6. Exit Group A.

This method effectively uses the geometry of one group to modify the geometry within another group by creating the necessary intersection edges.