How to cut-off border edges of a non-watertight object without closing them?

[ajz3d]

I have a VoxTree surface layer which contains a non-watertight object. I need to slightly cut-off jagged border edges. however if I use a Cut-off tool - apart of cutting, it also closes those border edges. How can I make a cut and preserve them?

[The Candy-floss Kid]

Does PaintHole do what you need?

[ajz3d]

Yeah, it almost does its job, but it leaves border edges a little bit jaggy and I need them perfectly straight with no tris crossing the cut line. Cut-off tool does exactly that, it's just that it also closes border edges at the same time (similarly to PaintHole with Remesh cut area turned on).

[The Candy-floss Kid]

Even with 'cut area exactly' option checked?

That leaves a nice tight line.

[ajz3d]

Even with 'cut area exactly' option checked?

Yes, I'm afraid so:

 

[ajz3d]

Now this is interesting! I probably found a bug in the Cut-off tool, but this is one of those times when a bug works to one's advantage.

I accidentally discovered that if I make a cut in such way that there's at least one border edge below the cut line then Cut-off tool won't close those edges.

[The Candy-floss Kid]

 

I accidentally discovered that if I make a cut in such way that there's at least one border edge below the cut line then Cut-off tool won't close those edges.

Hmm sound interesting - how do you add an extra border edge before using cut-off?

 

Something off/ peculiar with your results with 'cut area exactly' option  methinks - working here.

Possibly you've found another bug?

[ajz3d]

Hmm sound interesting - how do you add an extra border edge before using cut-off?

I didn't have to. I made a cut just a little above the lowest border edge(s) of the hole. This seems to be enough to make Cut-off not to close the hole and still results in almost perfectly straight cut. Then I zoomed-in on those untouched border edges and roughly moved their vertices upwards to match the cut line.

But if border edges weren't jaggy, I'd probably use the PaintHole tool to make a hole reaching from the border edges to just below the planned cut line first.

 

Something off/ peculiar with your results with 'cut area exactly' option  methinks - working here.

Possibly you've found another bug?

I'm not sure, but I think this depends on triangle distribution and the resolution of the surface. On high definition surfaces the jaggedness from the PaintHole might not be that noticeable as would it be with low-res geometry, but it's still there. For example, on the second image I selected a triangular area and the result of this is the green jaggy line which will also be the line of cut of the PaintHole tool (if "cut area exactly" is selected). But subdivide that mesh a couple of times and the jaggedness is barely noticeable. Barely, but it's there (3rd image).

[Tony Nemo]

What does "Remesh cut area" do?

[ajz3d]

I didn't try it on a closed mesh, but on open one, if PaintHole selection includes border edges, it will seal them like normally Cut-off tool does. Also, the geometry it creates will be very dirty (again, in this particular case).

Generally speaking I think some of the tools weren't written with open meshes in mind.

Edited May 29, 2014 by ajz3d

[The Candy-floss Kid]

 

I'm not sure, but I think this depends on triangle distribution and the resolution of the surface. On high definition surfaces the jaggedness from the PaintHole might not be that noticeable as would it be with low-res geometry, but it's still there.

I concur. Had never noticed it when taking a simple slice off the top - but yes it's there alright on closer inspection.

That said sometimes I get as near as dammit results too with edges -odd.