Intersect face; cut face problems


I’m an architect working with re-purposing old New England mill buildings, typically into apartments. My model needs to show all the apartments on every floor. Since this means literally hundreds of partitions, I want to use a partition component, rather than modeling hundreds of separate partitions. No problem so far. But the developer needs to know the square footage of each apartment. Normally I click on Entity Info and get a very accurate square footage.

But I’m having a nightmare of a time getting the partition components to cut the face of the floor. Not only that, but when I attempt using Intersect Face, hundreds of hidden lines are created that separate the floor into many triangular wedges, visible only with View > Hidden Geometry. This hidden geometry controls selecting the portion of the floor hopefully cut by the partition. Often the partition fails to cut the face. I’ve tried Intersect face with Model, with Context, with Selection. Sometimes that works, sometimes it doesn’t. I’ve tried employing Cut Opening when making the component. Sometimes that works, sometimes it doesn’t.

I’ve had many, many hours go down this particular SketchUp black hole. I need a reliable method of placing partitions that will cut the floor face every time. I’m attaching my current model. Thanks in advance for any help.



Oops! Didn’t see how to attach my model.


Model still not uploaded. Use the bar with an arrow icon 7th from left in the edit window.

But here are a couple of advance thoughts.

First, the fact that your floor gets triangulated by hidden lines is probably telling you that either it or your partition it is not planar. Small errors when drawing can cause this.

Second, for an Edge to cut a Face, they must both be in the same “context”. So, for example, if your floor is one Group or ComponentInstance and your partition is another ComponentInstance, the partition’s Edges will not cut the floor. One way to handle this (assuming the non-planar issues are cleaned up) is to open the partition for edit, select the bottom edges, copy them, close the partition and open the floor (if it is also a Group or Component), and use Edit->Paste in Place to create a copy of the edges in the same context as the floor. These Edges will cut the Face of the floor. With a lot of partitions, this isn’t a one-step process, but it will work.


Thank you for your reply.

That was my first post to the new Forum, and I was about to ask how one goes
about selecting to have replies e-mailed, when yours arrived.

I suspect you’re right-somehow my floor is not quite planar.

The building has an angled wing, and in going back and forth from wing to
wing, I’ve been resetting the axes.

I’ve still not mastered how to reset axes: instructions say to right-click
on the axis, then reset them.

Most times when I right-click on the axes, I do not get a reset option.

So I use the axis tool instead.

Sometimes it “takes”; other times it quickly reverts back.

I think what happened in one such reset is the blue axis got tilted about
one degree or less.

That somehow led to my making a not-quite-planar floor.

Sure wish I could fix it.

I tried copying the bottom of my floor slab, and placing it 1/2" above the
not-planar one.

Didn’t help.

But something else I noticed:

The piers on Level 1 are components.

My process was to place one on the floor, then move-copy others as needed.

When I go to Hidden Geometry, I see numerous diagonal lines tracing the
paths of each of these copied components.

I wouldn’t care about these lines, except they interfere with selecting
particular portions of the floor, namely one apartment.

I’ve tried erasing many of them, so you won’t see how many there were

Sorry to be so wordy.

Tried your suggestion for uploading my model, but I got an error message:
file is too large.

So here’s a link:

I’m going to be doing more such models in the future, and really want to
overcome these issues.

Thanks in advance,


If you love trees, you don’t use paper towels. ~ Yes! magazine


I got so frustrated with the non-planar floor that I just wiped it out

Copied a good planar Level 5 floor, and moved it down to Level 1.

All those ■■■■ diagonals somehow reappeared:

Any thoughts about what’s going on?



If you love trees, you don’t use paper towels. ~ Yes! magazine


Just fiddling with your model now. One immediate suggestion: use more layers to manage selective visibility instead of hiding things.

In the model for download, I’m finding that I can erase those triangulation lines without losing the level 1 floor face. I haven’t finished investigating why they are there.



Formerly I used layers a lot in this kind of work.

However, it got me into all sorts of trouble.

For example, when I’d want to add to a particular layer, I’d make that layer
the active layer and model away.

I’d often get a message something like: Your action has merged with geometry
a line on a hidden layer."

Linework became uncontrollable.

I posted on the former SU Forum, and I think it was Tully who advised me to
avoid layers for actual modeling, and use Outliner instead.

That guarantees that all geometry is in Layer 0, and has kept me out of that
particular brand of trouble.

To repetitively hide and unhide a lot of geometry, I set up scenes.

In this model I have used layers for the Google Terrain and for floor
height/window-spandrel templates.

If you love trees, you don’t use paper towels. ~ Yes! magazine


After looking closely at your model, I found that there are a lot of things that are slightly out of line with each other, slightly out of level, slightly out of plumb, etc… For example, the bottom of the partitions are not parallel to the surface of the floor. In the attached screenshot I drew construction lines through the bottom, front, and back edges of a partition. I then created CL’s parallel to the bottom at the points where the front and back CLs meet the floor. You can see that the front edge is above the floor surface, whereas the back edge is below! {edit: no that’s not quite correct. The floor is closer to the bottom at the near edge than at the far edge).

I can’t afford enough time to try to fix all the misalignments, I’ll have to leave you to do that. But here are some ideas to help avoid this kind of issues in the future:

  • create construction lines and helper rectangles based on the model axes to keep things vertical and level
  • pay close attention to inference engine snaps while drawing. They will cause new things to match the pre-existing ones

In addition, please reconsider what you were told about layers. You should never make any layer except layer0 “active” for any reason. You should only assign Groups or ComponentInstances to any layers except layer0. Following these two rules, you will always have all primitive entities on layer0 and can use other layers to control the visibility (which is independent of active) of the Groups and Components. Using the Outliner will also work, but has some drawbacks compared to using layers: You can easily put large numbers of Groups or ComponentInstances (e.g. an entire level of your model) onto a layer and turn its visibility on or off en-masse. Doing that via the Outliner is much more difficult and tedious. Items on a hidden layer are not revealed when you show hidden geometry, so you get less clutter. You only get the “merge with” warning when you have put primitives onto hidden layers - Groups and Components on hidden layers may provide inference snap points (which is occasionally confusing), but they can never merge with new geometry any more than they could if they were visible.


Thank you.

I’m facing a deadline, and will not try to fix all these slight

Instead, I’m creating work-arounds.

If I understand correctly what you wrote about layers, it is fine to place
components or groups on other layers, but all primitive modeling must be
done on Layer 0.

So in a final presentation of, say a 5-story building, if I want to be able

  1. Remove the roof
  2. Remove Level 5

  3. Remove Level 4

  4. Remove Level 3

  5. Remove Level 2

  6. Remove Level 1 Mezzanine

It would be safe to make each level a group, then place each group in a
separate layer?

It is a context of economic and ecological violence that shapes our moral
relationships with self, neighbor around the globe, and Earth itself.

` Cynthia D. Moe-Lobeda


So in a final presentation of, say a 5-story building, if I want to be able to:

Remove the roof

Remove Level 5

Remove Level 4

Remove Level 3

Remove Level 2

Remove Level 1 Mezzanine

It would be safe to make each level a group, then place each group in a separate layer?

Absolutely! That is just what I did while examining your model to get other levels out of the way while looking at level 1


I suspect your habit of hiding things is at the heart of your issue. You seem to have lots of hidden loose geometry lying around and if any of it is near the floor you are having problems with it will cause the face to split.
Here is a screen shot of a bunch of stray edge above the building, I imagine there are things like this within the structure causing you problems.


Box (?),

Thank you for your reply.

I too noticed all that stray geometry and wiped it out.

Didn’t help my face problems.

Worse, I have no idea how that stray geometry was created, especially way up

I guess I must have done it, but am nearly clueless as to how.

Maybe in the course of Intersect Face operations?

I have learned that when there are a lot of components, and they overlap (to
form connecting beams and demising partitions ) using Intersect Faces
generates a vast quantity of new geometry


If you love trees, you don’t use paper towels. ~ Yes! magazine


[quote=“jimshipsky, post:12, topic:8440”]
If you love trees, you don’t use paper towels. ~ Yes! magazine
[/quote]Do you really need to make a political statement after every one of your posts? However worthy your political opinions may be, this is not the venue for it. I can think of far more objectionable slogans or mottos one could use–should they all be tolerated because yours is? What, then, does that make this forum?



Sorry, Gully, for causing you to take offense.

I had no idea the replies I thought were going to only one person were being

This is the first time I’ve used the Trimble version of the Forum.



Well, Jim, that’s the kind of non-apology that politicians are known for. All it says is you’re sorry I took offense to something you said (implicitly because I’m hyper-sensitive)–there’s no remote acknowledgement that you were out of bounds. What’s the point of such an apology?



From the Forum Guidelines that you should have read by now


See …
Does SketchUp support layers? — SketchUp Help


I totally deleted Level 5, which was not perfectly planar, thus causing some of my difficulties.
I also discovered one corner was not perfectly 90 degrees, also causing problems.
I modeled a new Level 5 from scratch, being very careful to ensure a perfectly planar face with perfect 90 degree corners.

I created a new partition component and began demising apartments.
Then I began the process of trying to get the components to cut the face.
Sometimes Intersect with model or context worked like a charm.
Other times it didn’t, but Intersect plus explode worked.
Sometimes neither worked, and I resorted to drawing a rectangle on the face in order to derive the square footage.
Checking ‘Cut opening’ when creating the component had no effect.
I imagine I would need to go thru the window-making procedure for that to work.
Thus, I am still mystified as to what is going on.

I’m also mystified by my original not-quite-planar face: why does SketchUp “fix” such a face, resulting in the problems I encountered working with a softened or otherwise “fixed” face?


There is no way to be subtle about this, your model is flawed.
Your workflow is flawed.
You don’t seem to understand the basics of the geometry of Sketchup.
I have been through your model and it terrifies me, there are edges on layers unrelated to their faces, there are hidden bits everywhere, loose and grouped. There are too many fundamental problems to address in one thread.

You intersect things with other things without understanding what thing 1 and thing 2 will do. You talk about cut openings and window making procedures in such a way that leaves me totally mystified.

Spending some time learning or relearning the basic of the program will help you immeasurably.


Some things to consider

  • At all times leave basic geometry on Layer0, so do NOT assign another layer to these basic entities
  • Don’t overdo when using different drawing axes. If you really need them (like in your case) to switch between working on different wings, save (capture) their orientatoin in a few scenes (here two or three at most). Now you can switch from one to the other scene avoiding mistakes in different axes.
  • avoid hiding stuff without keeping track of what should be visible, only use it for temporary working on geometry (example: quickly hide a face to get behind it). Use layers (on grouped geometry) to contriole what should be visible.
  • Avoid having geometry slightly “out of line” (by say 0,01mm) when it is in the same context. New edges just snap to existing geometry in between on their way from start to target. I assume that is what happened here over and over. If possible, separate such geometry by creating groups or componentrs.