Mesh Retopology

Retopology = redrawing a mesh's topology while preserving its shape. The output of a scan is a soup of millions of triangles; you usually want a tidy quad mesh for animation rigs, sub-d modelling, UV unwrapping, or game-engine LODs. Pairs with Mesh Processing (cleanup before retopo), PBR Texture Libraries (textures after), Photogrammetry Software and Handheld 3D Scanners (the upstream meshes), and 3D & Spatial Design Tools for downstream Blender / sculpt work.

Auto-retopology (free)

• ★ Instant Meshes (Wenzel Jakob) — free, OSS (BSD); the field-aligned auto-retopology tool. Cross-platform, single binary, draws crease lines, outputs all-quad. Very fast, very good results on organic meshes. The default FOSS auto-retopo since ~2015.
• ★ Blender Quad Remesh / Remesh modifier — free, built-in; Blender's voxel + smooth + quad remesh modes. Quick way to get a uniform quad mesh; less directional control than Instant Meshes.
• Blender RetopoFlow — free, OSS Blender add-on (CrowdFunded; now community-maintained). Manual / interactive retopology brushes inside Blender; Polystrips, PolyPen-Plus, Strokes.
• Blender BSurfaces / Tesselator / Retopo MT — free / paid Blender add-ons; specialised retopo brushes.

Auto-retopology (paid)

• ★ Quad Remesher (Exoside) — paid Blender / Maya / 3ds Max / Modo / ZBrush plugin (~$100); the gold-standard auto-quad remesher. Better than Instant Meshes on many meshes; respects guides and crease curves.
• ★ ZRemesher (Pixologic / Maxon, in ZBrush) — paid; ZBrush's auto-retopo; the long-standing pro tool. Works great on sculpts.
• TopoGun 3 — paid (~$100); standalone retopo + bake app; common in VFX / games.
• 3D-Coat AutoPo / RetopoTools — paid; integrated retopo in 3D-Coat.
• Maya's Quad Draw + Remesh — paid; standard in big-studio pipelines.

Manual / hand-retopology

When the mesh has a specific edge flow (hands, faces, anatomy for animation), automatic tools aren't enough.

• Blender RetopoFlow — free; the FOSS standard for hand-retopo.
• Maya Quad Draw — paid.
• TopoGun 3 — paid.
• 3D-Coat Retopo Room — paid.
• ZBrush ZSphere retopo — paid (Pixologic).

Decimation as a poor man's retopology

When the goal is just lower poly count rather than clean topology, decimation is faster:

• MeshLab Quadric Edge Collapse — see Mesh Processing.
• Blender Decimate modifier — fast.
• gltf-transform simplify — for web glTFs; see 3D Format Converters.
• Simplygon — Microsoft; commercial SDK for game-engine LOD chains.

Texture / detail transfer (after retopo)

After retopology you need to bake the high-res scan's normals / displacement / colour onto the new clean topology. Tools:

• Blender Cycles bake — free; bake from high-poly to low-poly.
• xNormal — free; the classic Windows normal-map baker.
• Substance Painter / Designer — paid (Adobe); industry-standard texturing + baking. See PBR Texture Libraries.
• Marmoset Toolbag — paid; great baker + previewer.
• Mari (Foundry) — paid; high-end texture painting.

When to retopo at all

• Animation / rigging: yes, you need clean edge flow.
• Sub-d modelling: yes, all-quad is required.
• Game engine asset: yes, controlled tri count + quads bake cleaner.
• 3D printing: usually no — slicer doesn't care about edge flow.
• Pure visual / static prop: decimate instead.
• Reverse engineering to CAD: don't retopo a mesh; go via Scan-to-CAD / Reverse Engineering.

Pick this if…

• Default free auto-retopo: Instant Meshes.
• Highest auto-retopo quality, willing to pay: Quad Remesher (Exoside) or ZRemesher.
• Hand-retopology for face / hands / anatomy: Blender RetopoFlow (free) or TopoGun 3 (paid).
• Just need lower poly count: Blender Decimate or MeshLab QECD (no real retopology needed).
• Bake textures after retopo: Blender / xNormal (free) or Substance Painter (paid).
• Going to CAD parametric instead: see Scan-to-CAD / Reverse Engineering.