splatreg

Register Gaussian splats — align & merge two 3DGS scans into one SE(3)/Sim(3) frame.

gsplat renders your Gaussians; splatreg registers against them. It is the missing registration half of the Gaussian-splatting toolchain: the splat-to-splat alignment that SuperSplat / INRIA / geospatial users keep asking for, where today's tooling punts to a manual gizmo.

• Pure PyTorch — no meshing, no CUDA extension, no point-cloud detour.
• SE(3) and Sim(3) — the only splat registrar that recovers scale.
• Framework-agnostic — gsplat, Nerfstudio/splatfacto, INRIA, SuperSplat, custom; anything that speaks the standard 3DGS PLY or hands over means/covariance tensors.
• Honest diagnostics — ambiguous overlaps are flagged (info["ambiguous"], info["confidence"]), never silently wrong-posed.

30 seconds, end to end

pip install splatreg
splatreg align scan_a.ply scan_b.ply -o b_aligned.ply     # register + write aligned PLY
splatreg merge scan_a.ply scan_b.ply -o fused.ply          # register + fuse + dedupe

or in Python:

from splatreg import register, merge
from splatreg.io import load_ply, save_ply

a = load_ply("scan_a.ply")          # target (stays fixed)
b = load_ply("scan_b.ply")          # source (gets aligned)

result = register(a, b, transform="sim3")   # init="fast" by default, ~17 ms
print(result.T)        # 4x4 similarity [[s*R, t], [0, 1]], maps source -> target
print(result.scale)    # recovered scale (1.0 for transform="se3")

fused = merge([a, b])               # register + concat + dedupe the overlap
save_ply(fused, "fused.ply")        # opens in SuperSplat / any 3DGS viewer

How it works

flowchart LR
    A["splat A<br/>(target)"]:::s --> G
    B["splat B<br/>(source)"]:::s --> G
    G["<b>Global aligner</b><br/>super-Fibonacci SO(3) seeds<br/>+ batched trimmed ICP<br/><i>(or FPFH / learned)</i>"]:::g --> L
    L["<b>Levenberg–Marquardt</b><br/>multi-residual:<br/>ICP + Gaussian-SDF<br/>SE(3) / Sim(3)"]:::l --> T["T*  (4×4)<br/>+ merge / dedupe"]:::o
    classDef s fill:#e8f6f8,stroke:#17becf,color:#0b3d44;
    classDef g fill:#fff1ee,stroke:#ff6b5b,color:#5a1a12;
    classDef l fill:#eef7ee,stroke:#2e8b57,color:#143d22;
    classDef o fill:#f3eefc,stroke:#7d52c7,color:#2c1654;

1. Global init — a coarse pose from a dense super-Fibonacci rotation sweep + batched trimmed ICP (no local-minimum trap), with optional FPFH+RANSAC (init="robust") and learned GeoTransformer (init="learned") seeds for harder real scans. See Init modes.
2. Refinement — a from-scratch Levenberg–Marquardt core over ICP (point-to-point / point-to-plane) and splatreg's flagship Gaussian-SDF residual — a smooth signed distance field derived directly from the target Gaussians, with a closed-form, audited Jacobian — solving the full SE(3) or Sim(3) tangent.

Headline numbers

	splatreg	reference
Real-splat merge (103k Gaussians)	Chamfer 10.3 → 2.0 mm (5.1×), overlap 0.03 → 0.67 (22×)	naive concat
vs splat competitors (known GT Sim3)	5.2°	splatalign 15.3°, GS-Registration 36.3°
Sim(3) scale estimation	native	none of these do it
Official 3DMatch recall	91.5% mean	GeoTransformer ~92%, Open3D ~77%
Registration speed	~17 ms (fast)	Open3D 142 ms

Full record with reproduce commands: Benchmarks.

Where next

• Quickstart — install + the core workflows in Python.
• CLI guide — splatreg align / merge / info from the shell.
• Photometric refinement — new in v1.1: the opt-in stage for poses geometry can't see (symmetry / texture-only DoF), with the measured when-and-why table.
• PLY interop — splatfacto / INRIA / SuperSplat round-trip, and what happens to spherical harmonics under a recovered rotation.
• API reference — every public function, autodoc'd.