Erratic behaviour of edge intersect in simple geometry

@Step, I can’t see how you could call this a feature rather than a bug, the sequence Box mentioned.
What is the relation between what you are doing and his example.

@Box. This failure of correctly splitting a face into two or more faces has been mentioned several times in the past. I think even your example can be brought down to the breaking an unwritten rule in which SketchUp fails to create faces in a correct way. It has to do with splitting up an existing face with newly drawn geometry into two or more faces where bounderies have only one mutual vertex. I had to look closely at you example but yes, it is there.

Create the exact same shape within the large rectangular box but this time without that large face.
SketchUp doesn’t fail. In the end draw one of the large sides of the rectangle to fill in its face. All parts are selectable as single faces.

It is a long known (I would say) bug. Do not make SketchUp split up a face with only one mutual vertex in its loops.

p.s. Two simple examples:

  1. Draw a rectangle. Select one side and rotate it 180 degrees about the central axis perpendicular to this edge. You’ll get a flat buggy sandglass.

  2. Draw a rectangle and on its face create a triangle that touches in one corner by only one vertex.
    Selecting faces reveales an error.

Take example 2). Do the same but first delete the large face. Later fill in the large face by tracing one side of the rectangle. Selecting faces won’t reveale any error in split faces.

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Which part of all this haven’t I made clear.
You are even calling it a long term Bug, I am just bringing it to people’s attention.
I’m not specifically complaining about it or theatening to storm off and use some other software!
I am simply pointing out a distinct, repeatable inconsistency in the way edges interact with faces.
It’s what people do when testing software, if they find something that isn’t quite right they point it out so it can be fixed. They don’t jump on people and say that is the way it has always been so learn to live with it.
@Shep has simply brought another inconsistency from another thread here to help consolidate them rather than making more threads. It is wholly relevant if you read all the posts.

Box, was the first part of your last post addressed to me?
If so, like you I call this a bug, one that somehow needs to be fixed. But unfortunately it has been there for a long time.
I was trying to find a pattern in why your example shows this odd behavior and only pointed out that it also fits unwritten odd/incorrect rule of new faces sharing oly one vertex in their boundaries.
If you were offended, sorry about that, my bad choice of words I guess.

Since the bug is there, a workaround is to have a second mutual vertex in both loops and then slide one vertex on top of the other where it should eventually be.

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I’m Sorry Wo3Dan, I did bite there…
It was just that I know there are work arounds, I know how to fix it etc
It was simply that I found an easily repeatable sequence of drawing something that shows perfectly the problem that has plagued people from time immemorial and people keep telling me how to get around it.
I just wanted someone who had the ability to do something about it look at it so that they might be able to work out why it does this. I was being helpful but I’m only coming across as obnoxious.

@Shep, I have always seen the hidden geometry you show during operation like folding. But In my case, the display of hidden geometry disappears after I’m done moving/folding/whatever unless I’ve done something to alter the plane.

Try typing a value for rotation instead of angle snapping. This was discussed elsewhere but I can’t quickly find the thread.


Reading Box’s “bite”, (sorry Box;-) and rereading your (quoted) post I now see that you pointed to an entirely different weird behavior.
Somehow here SketchUp doesn’t like an input without having done the full operation.
As you said, typing in a rotation value before clicking an end rotation triggers the hidden lines.
Typing in a value after that second click makes hidden lines disappear immediately after numerical input. So does, as it seems, retyping the same value in the first case. This corrects the visible mistakes.
Odd behavior, to say the least.

28 posts and no reaction from one developer or SketchUp team member. Do they work on the solution and want to surprise us?

these bugs have always been there (or, at least for the past 11 years)… or, i’m ~100% sure the devs know of the behavior already.

it’s probably not a simple fix and (speculating->) involves base level changes to be made… possibly something to do with the way tolerances are handled… or, the line intersecting algorithm(?) sees an intersection has occurred and breaks the line where as the face maker doesn’t see it the same way.

but my point isn’t trying to guess at why it happens… just saying it’s likely this is a can-of-worms type of situation… seems like a basic bug but if it were a simple fix, i’m guessing it would be fixed by now… the bug(s) are likely tied to something deeper in the program and may be a much greater effort to fix than if it were a ‘regular’ bug.

From the release notes of 2015:

Face Finder improvements

We’ve mined and optimized the code for Face Finder, one of the core under-the-hood operations that make SketchUp’s magic possible. Face Finder is the code that runs whenever SketchUp automatically creates a face from coplanar edges. Think for a second about how often that happens. When we tested this sharpened code on large models, we found big performance improvements in operations like Explode and Intersect.

I have a similar problem. Sometimes I will try to draw a simple rectangle after carefully laying out the size and boundries with tape measure. I’ll draw the lines and can see the rectangle, but it stays just four lines and not a solid plane liike I want.

One of the problems with discussing this sort of thing is that without total context and careful analysis it can be difficult to tell a real bug from a user error. What you describe is so simple and basic that unless there is more going on than you state it seems likely you are making some mistake. Could you post an example?

Forgive me for not posting a graphic example however,
I’ll describe the anomalies I’m fighting with at this time,
a major one appears to be that some ( even totally straight lines )
appear to get into a condition where they behave like very finely dashed lines
and lack continuity so as to be utilized as the complete line I intended.

and the other Feature/bug is the fact that if I have two parallel circles and draw lines between the edges of said circles, I get random results that is to say sometimes it produces a surface in the area created, and sometimes it doesn’t. This is VERY frustrating in that I’m used to using commercial Cad programs such as AUTOCAD, but for hobby use, I thought I’d try Sketchup, however if I can not get consistent results, why bother?

It’s not quite clear what the problems are that you are facing.
Parallel circles as in one above the other? Or concentric?
Could you upload a model with examples and write some comments to what edges you mean and where you expect consistency in SketchUp creating faces, (a cylinder or a flat object?)

You can’t just connect the circles with random lines and expect to form faces. You have to draw them correctly or it won’t work. The lines must connect endpoints, and they must form a coplanar outline. You may need to subdivide quadrilaterals with a diagonal, making eventually a mesh of triangles.

Perhaps more to the point, if you’re not going to do it correctly, or don’t even understand what the objective is, why bother?


I’ve been trying to learn Sketchup and what I’m seeing is apparently some grossly inconsistent performance when it comes to lines and the way that lines work, sometimes I get a line that for all practical purposes is a finely dashed line and selecting it requires making a box around the whole thing to get it all or multiple select operations, now if I’m using sketchup improperly, where is the INFORMATION that will tell me what I’m doing wrong? Please throw me a bone here.

I’ll try to figure out the upload procedure, so I can show an example of what I’m attempting to do.
The goal of the design work is to be able to customize an automotive type design and I have seen other work by sketchup users who produce drawings of VWs and others that look really cool, however this is to be a from scratch design that is different than anything in current production.

An example would be most useful. It should by now be evident that people here are trying to help but are having trouble understanding what you are doing.

The Knowledge Base contains a searchable users’ manual and links to vast resources of video tutorials. You really should take yourself systematically through these to get a solid foundation in basic program operation before you launch off on some ambitious automotive design project.

I think you should focus on learning how to perform operations correctly the first time rather than making a poor guess at how to do something and then trying to figure out what you did wrong afterward. That’s about the most inefficient way there is to learn something.


I now get the limitation of the program in that if I want a surface, I will either have to manually create a mass number of triangles ( impractical ) or possibly find a plug-in that can help me out with this. I know its possible to generate a sphere and then using the scale tool mash it into a shape that is a pretty good approximation of what I’m looking for, but the real trick is going to be getting the dimensions correct. This is were these modeling programs are different from AutoCad in that one specifies dimensions from the very beginning and its all set, in a modeling program its a bit more tricky to assign dimensions and get the desired shapes. Any suggestions on a handy plug-in that aids in the production of calibrated size curved surfaces?