Turn a raw 3D scan into surfaces you can actually design with — without leaving Autodesk® Fusion®.

Scan STL Assistant is a guided reverse-engineering toolkit built around one simple gesture: PAINT the region you care about directly on the mesh, preview the fitted surface, adjust, validate. You stay in control at every step; the math does the heavy lifting.

PAINT, PREVIEW, VALIDATE
Select a mesh body, then drag the cursor over it like a brush — the selected triangles highlight in orange (Alt erases, brush size is adjustable). Click "Compute preview": the fitted surface appears overlaid in blue, with residual statistics (RMS and 95th percentile vs. your tolerance). Repaint, change the tolerance or the type, recompute as many times as you like. OK creates the final B-Rep surface — reusing the exact preview you approved.

PRIMFIT — ANALYTIC PRIMITIVES
Recognizes the five classic surfaces on the painted region: plane, cylinder, cone, sphere and torus (the shape of constant-radius fillets). Fits are metrology-grade least squares with outlier and tangent-leak protection: radii, axes and angles you can trust for hole patterns, mating faces and datum surfaces. The created surface is trimmed to the painted region — height AND angular sector — plus an adjustable overshoot margin in mm, ready for later trimming and stitching. An Auto mode picks the simplest type that fits your tolerance.

SURFFIT — FREEFORM SURFACES
For styled, organic regions (body panels, fairings, casings), SurfFit builds the SIMPLEST bicubic B-spline sheet that matches the painted zone within your tolerance: complexity is escalated only when needed, and a bending-energy smoother eliminates the wavy, noise-chasing surfaces that plague auto-surfacing tools. Spots the sheet cannot follow within tolerance are highlighted in red so you know exactly where to split the region. The sheet extrapolates cleanly beyond the painted boundary by a margin you set in mm.

BASEFIT — SCAN ALIGNMENT
One click re-aligns a freshly imported scan to the Fusion origin: detects the dominant plane (parting plane to XY) or the revolution axis (to Z), with PCA fallback. Sets a clean datum before any measurement.

MESHFIT — SCAN-TO-SCAN REGISTRATION
Best-fit ICP registration of one mesh onto another: merge multiple scan passes or compare a part against a reference, with overlap and residual reporting.

BUILT FOR REAL SCANS

• Tolerance-driven: you specify the fit tolerance in mm; every result reports its residuals honestly.
• Robust to scan noise, holes and uneven density.
• All processing is LOCAL — your scans never leave your machine, and no internet connection is required (dependencies are bundled).
• UI in English and French (follows your Fusion language).

Typical uses: recreating mounting interfaces and hole patterns from scanned parts, rebuilding fillets with their true radius, extracting reference skins from scanned bodywork, aligning and merging scan passes, reverse-engineering discontinued or one-off components.