Why do so Many Auto-retop Tools Spiral and Why do People Not Seem to Care?

flamingmonkey93

For context, my job involves taking 3d scans of furniture and retopping them to a more useable, renderable state. We do not however bring in or use colour scan data due to how a single piece of furniture will have numerous kinds of materials applied to it.
Naturally this is tedious. There are numerous ways to speed things up, with much more efficient tools and software like Topogun etc.

However, when it comes to just overall fully automatic retopping tools these always leave some sort of unsightly, and often unworkable spiralling geometry. 

So, to my question above really. 
You see so many of these auto-retopping tools and the praises sung by them, but if they constantly give spiralling geometry is this a result that is not actually cared about/effects the workflow? or is there just more work needed to be done from out side in order to make these auto-retopping tools work?

e.g. Are the spirals a non-issue, because of how the diffuse is brought in and baked onto the mesh. Or that they're painted in 3D with the likes of substance and thus weird seam placements are a thing of the past.

poopipe

if you're looking at conventional  (non-ML) algorithms there really aren't any very good ones for inferring a direction of flow from an arbitrary cloud of points cos it's just not a thing you can express mathematically. 

ML is probably the answer to this one.  it's an ideally suited problem ... 
That of course means you'll be waiting a while for anything decent to show up.  Nobody's funding anything useful when there's money to be made generating porn and gathering personal data from users



I've not poked around much in several years but zbrush's guide painting was probably the best way to handle the issue in practice. 

gnoop

If a 3d scan is really hi res   with sharp edges  Zbrush  Zremesher with "detect edges" on  does pretty nice job actually without much of spiraling  edge  loops.  As well as 3d max one.    The issue are things like blades  with triangle  profile  where it can't recognize the cutting edge .       Boxes and cylinders with holes   are often sort of  okish.

Also i prefer to use topology brush with Shift  to draw straight lines on hard surface objects . Zremesher works with any curve brush.

iam717

zbrush's guide painting was probably the best way to handle the issue in practice.

Yeah, & op, when i care to do it i do the zremesh,topogun route to cut out the b.s. if you want a method to try, but i agree.

Couldn't they just use patterned geo with proper topology to be unified with the math-algorithm they use(like do it like this, patterning and not spiraling,"lazy-method")? like cylinders for clothing and pretty much anything else, except for some hard-surface works. (+ abnormal/unique creations/cases).//fix,readability.

Michael Knubben

The spirals are an issue, it's just a hard problem to solve automatically. Giving the algorithm facegroups/materials to cut the mesh up into multiple parts and to mark hard edges helps, but it's still hard to get a usable mesh out without manual fixing.

I use Exoside's Quadremesher (the same algorithm as Zbrush's) and it's nice, but needs manual work to guide it.

Shrike

I would look into houdini, they recently were showing some good looking scan optimization features I think but never did it myself

Eric Chadwick

3ds Max has some really good options lately for tweaking how the retopology is generated, worth a look 

https://www.youtube.com/watch?v=Pg2Nm-fwyME

oglu

If you cut your char first into parts its much better.
https://youtu.be/B6tS1nPaFAU?si=Igw-2MZhuHMyj9cn

gandhics

In 3dsMax, you can just add slice modifier and set to refine mesh. Then, choose to constraint to selected edges.

gandhics

Shrike said:

I would look into houdini, they recently were showing some good looking scan optimization features I think but never did it myself

Houdini quadremesh quality is simplely unusable.

Shrike

Is there any quadremesh thats good? C4D has zbrush quad remesher, and that also seems unusable for any hard surface
Retopo is really a topic for machine learning to solve, Im surprised nobody has solved that yet since its a very predictable pattern and mostly uses one single data type. Very strange how we can't quad remesh a simple box.

poopipe

Shrike said:

Is there any quadremesh thats good? C4D has zbrush quad remesher, and that also seems unusable for any hard surface
Retopo is really a topic for machine learning to solve, Im surprised nobody has solved that yet since its a very predictable pattern and mostly uses one single data type. Very strange how we can't quad remesh a simple box.

There's more money in solving easier problems at the moment - someone will get around to it eventually though I expect

Eric Chadwick

Did you see the CAD & text parts of the vid above? https://www.youtube.com/watch?v=Pg2Nm-fwyME&t=790s

Works pretty well on really difficult hardsurface CAD stuff.

Shrike

It still cannot even do a straight corner and thats really nasty to fix or barely fixable
Also with this resolution yes, but real hard edge stuff is much worse

Neox

that people don't care is probably not really a thing. they care, they realized that automatic solutions are for the most part not good enough, they occasionally test whats new and then go back to doing things by hand, if quality and not time is the constraint here.

ZacD

I'd be happy with an auto topo tool that biased to the world/XYZ grid in order to place loops and avoid spirals. You can kinda force 3d coat to do that with a bunch of control loops and symmetry, but it seems crazy there's not one tool that really tries to do it automatically.