# How can I join the geometry of intersecting faces/planes and then remove parts?

As a small example, I have two intersecting faces, both part of a larger object. Without destroying the textures, I'd like to connect them (so they share vertices) where they intersect. That way I can create edges and delete whatever sections I wish to remove. Here is a small example:

My cumbersome method so far is to subdivide an edge, slide the vertex to where it looks like it meets, draw new lines, delete original faces, create new faces, and remap the UV. Is there an easier way?

Below is a larger example. The following link is a small piece of my blend project of which I'm trying to do this maneuver on. In short, I want to remove all the green on the inside of the brown and all the brown on the inside of the green. I hope that makes sense :-)

http://www.pasteall.org/blend/29003

example2 http://www.pasteall.org/pic/show.php?id=70940

• Did you try the Knife tool or Knife project even? (I believe the latter requires both faces being separate mesh objects). – CodeManX May 7 '14 at 0:22
• I can use the knife to estimate a cut on, say, the red piece, but there's no guarantee that the new edge is perfectly aligned with the brown piece. Then further, I'm not sure how to make that new edge an actual part of the brown piece without simply creating a whole new face. It does save me one extra UV remapping though. – CodeMonkey May 7 '14 at 0:46
• You may want to look at this addon – sambler May 7 '14 at 3:40

## Separate, add Boolean Modifiers, then Rejoin

You can achieve this by:

1. Separating the different planes into different objects.

2. Adding a Boolean modifier set to either Union or Intersect on both of your planes, then applying both modifiers. The result is that both planes will have perfectly made edges where they intersect.

3. You can then Join them into one mesh and edit parts of each as you wish without disrupting the textures of either plane.

For example, here there are 2 intersecting planes, both part of one object:

Here's how you begin:

1. Select the object, enter Edit mode (TAB) and then separate each plane to be it's own object with the following method:

• Select one plane → Separate (P) → Selection

Repeat this until each plane has been separated, then exit Edit mode with TAB.
NOTE: Do not move either plane from it's location so they will still be in the proper place when you rejoin them back to the larger object at the end.

2. Add a Boolean modifier to each plane:
Select plane → Object Properties panel → Modifiers tab → Boolean

• Set the Operation to Union or Intersect

• Set the Object to the other plane

For example, here is the modifier added to the "Blender Logo plane":

And here is the modifier on the "Blank plane":

3. Click the Apply button on both modifiers

4. Select both planes and the larger structure they were part of, then use Join (CTRLJ) to join them back into one mesh again

The result is you now have one mesh object with perfectly marked edges where the planes intersected, and you can edit the faces as you wish without disrupting the textures:

NOTE: I'm using 2.70a and there may be a bug in the Boolean modifiers: I noticed that sometimes when I clicked "Apply" on the modifiers, the planes disappeared sometimes, and other times they behaved oddly. If this happens, just use Undo (CTRLZ) to go back to before you clicked "Apply" and try again. Eventually it worked for me.
:)

• This looks like an amazing answer and I'm attempting to try it out. I'm thinking we have a bit of a difference, however. When trying to apply the Boolean modifier, it tells me that I can't do so in edit mode. But if I'm not in edit mode, then I cannot select the plane I want to do this on. They're not their own separate objects, they're two planes within the same object. Must I first break the planes apart? Thanks for the response, btw! – CodeMonkey May 7 '14 at 16:51
• Ah hah! I didn't realize the planes were part of the same object. Yes, for this technique, you'd have to separate the planes into different objects. I'll update my answer to show you how to do that. – Thom Blair III May 7 '14 at 17:12
• Ok, but fyi, if I did make them separate objects, they are still just part of a much larger object that I'd want to reconnect again. – CodeMonkey May 7 '14 at 17:22
• Ok, I'll make sure I answer that part also. :) – Thom Blair III May 7 '14 at 17:29
• CodeMonkey, I just heard from the Blender programmers/developers and they said the reason the booleans do not work on planes is because booleans are only designed to work on manifold meshes, i.e. meshes that have an inside. So, if you want to give your planes a very minimal thickness, you can then use booleans on them. If you add a Solidify modifier to your plane, the booleans should then work. Hope this helps! – Thom Blair III May 8 '14 at 15:54

Select the face, which you would like to cut at the intersection and press Ctrl+F.

Then select "Intersect (Knife)".

Done!