SNAP3DPhysically Grounded 3D Parts for Assembly from a Single Image

Yu-Rou TuanHao-Tang Tsui Nicolás UgrinovicKris KitaniXiaoxuan Ma
Carnegie Mellon University
arXivsoon Code Video

TL;DR We propose a physics-guided framework for improving single-image part-aware 3D generation with physically compatible geometry and stable connections.

Limitation of Prior Work

Existing methods generate visually complete parts without ensuring they form a valid physical assembly. Neighboring parts interpenetrate, lack valid connections, or collapse under gravity.

Input image
3D generator
Parts pulled apart, overlap in red
simulation
The same parts under gravity
SNAP3D
Our result under gravity

Input image

Red is geometry buried inside a neighbouring part

Released under gravity in simulation

Ours: holds together in simulation

Approach

We resolve inter-part penetration, recover a contact graph between neighboring parts, and introduce parameterized connectors refined against physical simulation.

Overview of the framework
Given part meshes from a part-level 3D generator, the three stages run in order. Bottom: the baseline parts collapse under gravity while ours settles and holds; the exploded view shows the generated peg-and-socket connectors.

Comparison

Every assembly is released under gravity exactly as generated. Parts that look complete are not necessarily physically realizable: they interpenetrate, have no valid contact surfaces, and fall. Our method makes them realizable.

rigid-body physics simulation
Input image
Ours
XPart
OmniPart
PartCrafter
Triceratops
Input image
Ours
XPart
OmniPart
PartCrafter
Robot
Input image
Ours
XPart
OmniPart
PartCrafter
Minifigure
Input image
Ours
XPart
OmniPart
PartCrafter
Signpost
Input image
Ours
XPart
OmniPart
PartCrafter
Input image
Ours
XPart
OmniPart
PartCrafter
Lantern
Input image
Ours
XPart
OmniPart
PartCrafter
Snowman
Input image
Ours
XPart
OmniPart
PartCrafter
Water blaster
Input image
Ours
XPart
OmniPart
PartCrafter
Armchair
Input image
Ours
XPart
OmniPart
PartCrafter

What Each Stage Fixes

Each stage added cumulatively to the same input decomposition. Geometry editing removes penetration, connectors provide the largest gain in stability, and physics-based optimization fixes the remaining cases.

Office chair

Input photographed on a phone · every stage shown in physics simulation
Input image
inInput image
1Part generation
2Geometry editing
3Connector init
4Connector optimization

Real-World 3D-Printed Assemblies

The exported parts go to a desktop FDM printer and join by hand, with no glue and no fasteners. Each row shows the input image, the parts as printed, and the object after manual assembly.

Printing on a Bambu Lab A1 mini · PLA
Every object printed and assembled
Ham hock3 printed parts
Park bench7 printed parts
Triceratops7 printed parts
Gorilla8 printed parts
Spacesuit toy3 printed parts
Cannon8 printed parts
1Input image
Input image — Ham hock
Input image — Park bench
Input image — Triceratops
Input image — Gorilla
Input image — Spacesuit toy
Input image — Cannon
2Printed parts
Printed parts — Ham hock
Printed parts — Park bench
Printed parts — Triceratops
Printed parts — Gorilla
Printed parts — Spacesuit toy
Printed parts — Cannon
3Assembled
Assembled — Ham hock
Assembled — Park bench
Assembled — Triceratops
Assembled — Gorilla
Assembled — Spacesuit toy
Assembled — Cannon

BibTeX

@misc{tuan2026physicallygrounded,
  title  = {SNAP3D: Physically Grounded 3D Parts for Assembly from a Single Image},
  author = {Tuan, Yu-Rou and Tsui, Hao-Tang and Ugrinovic, Nicol\'as and
            Kitani, Kris and Ma, Xiaoxuan},
  year   = {2026},
  note   = {Preprint}
}