Mesh intersections and doorway cutting

[ekimmai]

Okay, another cry for help......

I've been exploring Boolean operations (Difference etc) to try and find the best way to cut out a section of a mesh where a tunnel entrance intersects with a rockface (to open as doorway as such). When I use Boolean I get faces disappearing where I don't want them to too and my vector count shoots through the roof (with desimate no longer functioning on the resultant mesh). Please could anyone advise me the best way forward?
I would like to avoid just subdiving and cutting out smaller and smaller faces manually in a hope the "tunnel-entrance" looks half-decent :\

Uploaded an image if that helps. I have an example blend file but cannot upload.

Tunneldoor.jpg (117.03 KiB) Viewed 3900 times

THANKS
Mike

[Moiety Jean]

I have similar issues all the time with my very complex mesh.. the desire to cut into it just so, and at my current knowledge level this requires a lot of manipulating vertices by hand. On a mesh of nice, even quads like you seem to have there, using V key to "rip" vertices in two (while retaining their attachment to the faces on one side of them) is sometimes helpful to open a hole in the middle of a mesh.
http://www.blender.org/development/rele ... h-ripping/

But, I'm beginning to think (without having researched this enough, or looked up tutorials) that Retopo tools may be what I'll need to more easily create vertices where I want them on my complicated underlying shape, if Retopo tools work like I suspect they do.
http://www.blender.org/development/rele ... 43/retopo/

Any other thoughts?

[edit: I should add that I was having the exact same problem with trying to use boolean intersections. I was trying to create an intersection of two cylinders, using nice, manifold meshes subdivided cleanly into quads (rather than triangles), and the intersected object would be full of jagged holes on the side opposite the intersection, despite my care in selecting all of the objects before intersecting them. I ended up abandoning this method and opted to join meshes by hand, which has taken me months.]

[ekimmai]

Thanks MJ, glad to hear I'm not alone in these "trials".
The vertices ripping is a new idea to me and looks useful for many purposes - I shall have to practice! The retopo technique seems very similar to Curve modifiers (which I used to create the tunnel by linking it to a Nurbs Curve) but with a more 3D angle.

Taking my example (as per screenshot) one would think it might be straightforward to just select the surface encompassed by the doorway and delete. To avoid the problems caused by Boolean techniques I have tried taking a duplicate of the tunnel edge and using that alone to obtain the "Difference" between the meshes but this still produces strange results. My next thought was to manipulate the rockface quads until the doorway appears within one quad face only - with the hope that this will reduce residual effect. I am not feeling very hopeful!

If all else fails I will probably end up creating a jaggered hole in the rockface, approximating to the tunnel entrance, and then lay an additional archway (resembling the l'arc de triumphe in shape) in front of the entrance to hide the "mess". Ideally though I wanted to retain the effect of a cave entrance (hole cut straight into the rock).

On a side note, do you know the quickest, neatest way to create a floor to my tunnel? (perhaps avoiding the need to lay a second plane/mesh underneath).

[Moiety Jean]

Not knowing how familiar you are with Blender it's difficult to advise you, but it sounds like you need to do a little tweaking of your vertex positions by hand. What I would do (and keep in mind I'm not the expert.. I can get the shapes I want but my methods may not be the most efficient) is rip a gap, and then adjust vertices on the wall plane until you get a gap that is approximately the same size and shape as the opening of the tunnel. I'd then adjust the vertex count and positions on the tunnel edge until they line up with the gap's vertices, and then I'd begin merging (with two vertices selected, Alt+M to merge them at your choice of positions) gap vertices with their nearest, corresponding tunnel edge vertices until the tunnel joins smoothly with the wall into one continuous mesh. You may need to reduce the number of vertices that makes up the shape of your tunnel to do this comfortably. For the floor I'd just select bottom edges opposite each other and use F key to make a quad face between them.

[Grogyan]

Other than using booleans, there is one other method, but I can't say how useful it is as I have only ever done it once, that being for my shell.

If you have drawn your doorway the way you want, Blender allows a method in which you can join vertices from one mesh to the other mesh, then you can just use the delete key to delet the faces that are blocking your entrance

[ekimmai]

Thanks guys. Ripping and merging sounds like the way forward for me. I'll give this a shot over the next few days......

[Chacal]

I do as Moiety Jean says. I'd rather do it by hand than trust booleans.

[Jojon]

While I too prefer to do these things by hand, I just tried doing the boolean thing and saw no unnecessary splits done. A few observations:

The operation assumes we are working with volumes, rather than single surfaces, so the resulting mesh will consist of the cliff face that you have cut a hole in AND any parts of the cutting tool that is "inside" the cliff, i.e. in the opposite direction of its normals. Just delete all residual tunnel-section faces and you should be fine -- you may want do use only a duplicate of the last tunnel section, rather than the whole length, to reduce the number of stuff to clean up.

If you want a sharp cut, you may want to keep the tunnel and cliff separate (i.e. no common vertices), because Plasma shades according to vertex normals, not face normals and if you have a 90 degree corner, the shading for the two face edges that meet there, will be shaded as if they were both facing the same direction (45 degrees relative to their actual facing - tick vertex normals in the mesh tools to see), which works well for rounded surfaces, but less so for pointy ones. If you still want them connected, you can add extra vertices near the corner, to confine the "rounding" to the very edge -- this does result in a few extra faces though. Then again, a slightly rounded corned looks better than a razor sharp one. :7

[ekimmai]

All sounds very technical and hopefully one day that will all make sense to me

I have managed to complete the tunnel entrance quite quickly using the following procedure (which is probably not the best but seems to work so far!):

1. subdivided tunnel faces near to entrance in order to select, duplicate and seperate (as new mesh) an entrance area for the tunnel. Decimated this new object until about 14 vertices remaining round arch.
2. Joined this new object to the rockface (ctrl-J).
3. Deleted rockface quads covering the tunnel entrance to give first picture below.
4. Formed new faces by selecting combinations (3 or 4 at a time) of the cliff and tunnel-entrance vertices. Gives 2nd picture below.
Done! (Could have used merging of vertices I guess instead).

Thanks for all the advice as this has really helped me work out the possible approaches and get a reasonable result (I think).
Mike

tunnel_prepn.jpg (150.84 KiB) Viewed 3744 times

tunnel_done.jpg (186.59 KiB) Viewed 3744 times

[pappou]

Man, that looks super-good to me.
Thanks for putting up your detailed solutions for attacking the cave wall.