Please Help: How do I make Straight parts in corners with Shrinkwrap & Sub Surface?

Hey guys, i’m trying to model a helmet. So what i did was shape a simple quad sphere to model from it’s basic shape there.

the problem is, i can’t make the corners at the base of the helmet straight, even if i already scaled Z to 0. Also how do i make the front part near the cheeks straight?

Thanks in afvance

I’m not entirely sure it’s possible to get truly straight lines with Shrinkwrap and Subdiv.

You can approximate more by duplicating and applying one shrinkwrap modifier to snap vertices closer to final positions. Even more if you apply subdiv, but I assume it’s not a desired course of action at the moment.

Have you tried using a project method in the shrinkwrap modifier? Specifically one along an axis aligned with the view you are showing?

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Interesting technic. Did you copy your base with lesser subdiv and shrinkwrapped it on the base ? If youhave a subdiv modifier on on the helmet it may do this… front straight: Maybe rotate all so you can scale in Y and re-rotate?
(Last edit before posting, because @StrayBillie and @LordoftheFleas annswered while i was typing…)
I meant applying the modifier… so no warp after…

Oh, that’s a good idea!

How about this:
before ‘main’ Shrinkwrap Mod add another one with Project Method on X-axis and assign to it a Vertex Group (of “border” vertices)


Thanks for the ideas guys. by the way, i followed your instructions and got the lines straight. May I ask how you got the corner sharp without creasing?

Screenshot 2021-12-04 201129

Used “Simple” in Subdivision… which probably won’t help you since you’ve got a curved line above.

by the way, is it normal to get these artifacts (shrink wrap acting weirdly for vertices near the axis where you chose to project.

When i chose X axis, the vertex where at the center looks weird.

when i choose Y the side of the helmet looks weird.

You may wanna distribute the vertices mannually in a smoother way or even using the sculpting smooth tool. The inner bulging seems to come from unroundness of the border curvation.

Hello again. My internet connection just disappeared a few days ago while i was typing this reply :’) so don’t know if it’s still relevant. And don’t have access through my pc yet, so no screenshots either atm.

Anyway. This thing happens because of the new vertices in border Vertex group (due to subdiv creating them). They all have weights between (but not including) 0 and 1. They are affected by Shrink-wrap accordingly.
With Vertex Weight Modifier you can edit them by removing from Vertex Group any vertex that has weight value less than 1. Place it before Shrink-wrap.

I can maybe attach screenshots later if still needed.

Yes please. i don’t know what i’m doing. thanks in advance

Ok. Still experiencing connectivity issues, will try to reply properly when I get around the problem =)

So. You’ve got a vertex in Vertex Group with a weight value of 1. And the neighboring vertex outside said group has weight = 0.
And in-between there’s a linear (i think) gradient of values from 0 to 1. When Subdiv Mod generates new vertices it assigns them appropriate weights from that gradient: with one subdivision level there’s a new vertex in the middle with weight = 0.5, with two subdivisions there’s 3 new vertices with weights 0.25, 0.5 and 0.75, etc…
When you use a Vertex Group in a modifier it will have all these values for new vertices. So in this case Shrinkwrap affects not only border vertices that you assigned but all the new ones nearby as well.

(Here’s what it looks like in Edit Mode with Viewport Overlays > Vertex Group Weights checked)

And this particular shrinkwrap with X-axis Project reacts weirdly (vertices get offset to X+ side). Why? No idea. Someone smarter than me should explain these things…

Luckily, there’s a modifier to edit weights.
We can remove vertices from a certain group if they have value below given threshold (less than 1, in our case). Yay!

Like so:

Now you should have a Vertex Group with only border vertices in it.
Place that Mod above shrinkwrap and that should solve the issue.

PS. I apologize if this reply got too… convoluted.

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thanks bro. it worked!