Why won't these faces intersect all the way?

I’m trying to intersect a mesh of land with a rectangular box in order to separate the face of the mesh in a perfectly rectangular area. I create a group that I placed over the land mesh (the big white box) and put that group inside the land mesh group. When I select “Intersect Faces > With Model” it draws NEARLY all the lines of the rectangular group except this specific corner.

I’ve tried a bunch of combinations but for some reason this particular part of the land mesh refuses to intersect the same as the rest of the mesh.

Any suggestions?

  1. Here’s where the white box and green mesh are intersecting.

  1. After the “Intersect Faces” option is applied, the new intersect lines seem to appear everywhere BUT this specific area which prevents me from separating the faces of the land mesh.

  1. With Hidden Geometry visible, you can see there are areas that simply don’t accept the new lines. They seem to be fine everywhere else.

Here’s a copy of the SKP file that I’m wrestling with in case anyone wants to dig in directly.

Box with Land Mass.skp (3.7 MB)

What happens if you scale everything up by 100 or 1000 before intersecting?

The scale is already pretty significant (1,500 ft I believe) but what were you thinking that might accomplish?

Also, worth noting I tried “Draping” a flat plane on the land mesh and that left me with the same issue.

If the land consists of a very fine mesh, intersecting could cause problems due to SketchUp’s trouble to create tiny geometry.

It seems to me that tweenulzeven has given you the right answer, wilschroter.

Here’s why I think so.
First of all, I moved the Component 10AC and the Group Box to the top level.
Screenshot 2021-07-22 015334

Then I intersected the Box with AC10 and got the same result as you did.
Then I intersected AC10 with the Box and got the same result as you did. Selecting AC10 first meant it was a two hour wait for the result.

Then I ran the “CleanUp3” Validity Check which also runs SketchUp’s native “Fix Problems” routine.
As you can see, this also took nearly two hours.

Screenshot 2021-07-22 014202
Screenshot 2021-07-22 014239
Finally, I intersected the Box with AC10 again. It’s fixed the corner, but there are still gaps elsewhere in the line of intersection.
Screenshot 2021-07-22 020811