Modeling on top of a dxf

I have dxf files of the floor plans of a 6-story building. I’ve imported them to SU, making each a locked group and assigning it to a layer of its own. Next I’d like to build a SU model based on these plans. I’ve drawn a floor plane on top of the first floor dxf, then made that plane a group. I assumed that when I opened that group, any modeling I do there will be separate from the dxf. But not so. Sometimes lines I attempt to draw within the group respond to the locked dxf instead of the geometry in the open group. For example, if I attempt to draw a line from one side of a rectangle to the other, sometimes the line registers in the open group as a thin line. Other times it registers as a thick black line, not integral with the geometry in that group.

How can I isolate the dxf and prevent geometry in my new group from connecting to the dxf? Help will be greatly appreciated.

Geometry in Group A does not interact with geometry in Group B. Honest. Therefore, you must be missing some relevant detail in your description. It would be useful to examine the model.


Here’s a link to my model:
To see where I’m having this issue, have visible Layer 0, Level 1, Level 1dxf.
Open the group (Level 1) containing the floor plane and brick wall.
Try drawing lines on the floor plane, ending the lines at points in the dxf.

With those three layers visible, a line drawn on the floor plane, where the brick wall has not yet been pulled up, does not register on the geometry in Level 1. It appears as a thick black line. Make the Level 1 dxf layer not visible, draw the same line, and it WILL register with the geometry in Level 1, appearing as a thin black line.

Better yet, I’ve added a scene to my model, named “two lines”, that shows my issue. One of the lines lies entirely within the Level 1 group and appears thin. The other line, the thick one, seems to me to have one end in the Level 1 group and the other end in the Level 1 dxf group.


The dxf layers contain a great deal of information I’d like to use in building this model, but it’s very frustrating to have some geometry fail to remain with the open group.

SketchUp’s inferencing system will snap on every visible geometric feature in your model, regardless if it is inside or outside the group you are currently editing. The “thick” lines you see are probably snapping to some point that is outside the current editing context and not on the face the edge is supposed to cut.


@jimshipsky, tip: instead of naming groups “level …” use names that seem to refere to layers or level of modeling context. A first nested group or component is in level 2 (modeling context) regardless of its name.

Thick lines are profiles that do not yet split a single (flat) face into two separate coplanar faces.
It can be in the same modeling context as thin lines. So it has nothing to do with edges “running from” one group to another. As Anssi said, the cursor may snap to geometry in another context, say your level1-dxf lever geometry. But it is definitely drawn in your current modeling contest, your opened level1 group. Although some edges were drawn (inadvertently?) whit this group closed again.

Just to amplify what Anssi and Wo3Dan have said, here are your two lines. The thick one doesn’t quite reach the end of the face until I move it.


And on an unrelated but import note, you need to look at face orientation.
Un hide all your layers and look at your model in monochrome. You should be seeing a majority of white faces but you have many blue/gray back faces showing.

Gentlemen, thank you for your input.
Two thoughts.

  1. Gully, at first I thought you were onto something, where you wrote the ‘thick’ line didn’t quite split the face. I assumed that meant the line didn’t quite reach the edge. But when I enlarge it to the max, it seems it does go all the way to the edge. At this point I think the issue is that one end of the ‘thick’ line has inferenced to the geometry in the open group, while the other end has inferenced to a point in the not-open dxf group/layer, as Anssi wrote.
  2. At this point I’m thinking there is no solution to this dilemma; that Anssi’s thought describes what is going on. If I draw quite a few lines from edge to edge, most of them split the face in the open group, but occasionally one will inference to the not-open group, and I get a thick line. Since I need to use the not-open group as a guide in adding detail, it seems I just have to live with this, and any time I get a thick line, delete it and try again to avoid the inference point in the not-open group.

Box, in my preliminary sketching on upper floors, I intentionally reversed some faces. Is there some danger in having both front and back faces present?

Imported geometry often exhibits poor intersections, and sometimes the errors are too small to see clearly. However, when I snapped the endpoint to the nearby edge, getting positive feedback from the inferencing engine, the subject edge clearly changed from a profile to an ordinary edge, meaning it now splits the entire face.


Gully, that’s helpful.
I tend to work too fast, and not read the inference notes.
If I slow down and pay attention, I get one of two inference notes:

  1. on edge (result [most of the time, but not always]: a thin line that splits face)
  2. on edge outside active (result always: thick line)

you can use wireframe mode, and move copy to help avoid the underlying endpoint snaps…
it can be very fast when your not trying to make a gif…