AECbytes Tips and Tricks Issue
#4 (March 8, 2006)
Hiding Edges During Intersection in SketchUp
Independent Writer and Consultant
Say you have two objects and you want to trim
each object using the other object. In other words,
you want to use Object A to trim Object B, and
then use Object B to trim Object A. This is not
so straightforward, because once Object B is trimmed,
SketchUp no longer considers it to intersect Object
The example used to illustrate this trick is
a skylight. Start with a box and insert a Sphere
component (found in the Shapes
folder of the Component Browser).
Move and scale the sphere so that the top sticks
out of the box.
Two intersection cuts are needed. First, the
top of the box needs to be cut to insert the skylight.
Second, the sphere needs to be trimmed to remove
the section inside the box.
For the first cut, right-click on the top face
of the box and select Intersect with Model.
This creates intersection edges where the face
meets the sphere.
Hide the sphere (do not delete it) so that you
can see the intersection edges.
Make the skylight hole by removing the circular
face within the top face.
The next step is to cut the sphere. Unhide it
and open it for editing (right-click the sphere
and select Edit Component, or
just double-click the sphere).
With the sphere open for editing, right-click
on it and run Intersect with Model
again. No edges are created.
Why does this happen? Because the top face of
the box has already been cut, and no longer passes
through the sphere. So nothing is being intersected.
Here's the solution: First end the component
editing. Then select and hide each
of the intersection edges previously created on
the top face. There should be several
small edges (segments of the intersection circle),
and you can select groups of edges at a time,
using left-to-right selection windows.
Now open the sphere for editing again, and run
Intersect with Model. This time,
the intersection edges are created on the sphere.
Because the first set of intersection edges was
hidden, SketchUp was tricked into thinking that
the top face was still whole.
Now you can delete the lower part of the sphere.
If you assign a transparent material to the partial
sphere, you can see that both the sphere and top
face of the box are now cut.
Note that if you had exploded the sphere in the
beginning, only one set of intersection edges
would be needed. These edges could be used to
trim both the face and the sphere. But imagine
a case in which you're creating dozens of skylightsit's
much easier to keep the component intact so that
when you edit one, you edit them all.
About the Author
Bonnie Roskes is the author of a number of books
on SketchUp, including the recent "Mastering
Piranesi: version 4" and "The
SketchUp Book: version 5." She is the founder
of F1, a
technical documentation and training company,
which does project work for several CAD/CAM companies
such as updating manuals, online help, and creating
tutorials. In addition to SketchUp, she has authored
books on OneCNC, and Piranesi (soon-to-be released).
Bonnie has a BS and MS in structural engineering,
and worked for several years in bridge design
and analysis before moving to tech writing. She
can be reached at: email@example.com.
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