Anvil Interactive Solutions

Posted on Oct 29

[RELEASE] AIS Unit & Scale Doctor — Fix Blender unit/scale issues, profile-aware rulers, and guarded FBX/glTF export

#programming #python #design #tooling

Correct size, correct axes—every time.

Why this exists

If your mesh looks right in Blender but wrong in engine, you’re probably fighting:

Unapplied or non-uniform scale
Negative (mirrored) scale & flipped normals
Parent objects with scale ≠ 1
Scene unit mismatch vs target engine

AIS Unit & Scale Doctor solves that, end-to-end.

Key features

🧭 Profile-aware units & axes Choose a Target Profile and the tool adapts:
- Unity (meters, Y-up)
- Unreal (centimeters, Z-up)
- glTF (meters, Y-up on export)
- CAD (millimeters) Rulers and axis lines are remapped to match the profile’s up/forward, so what you see in the viewport reflects what the engine expects.
🔎 One-click detection Flags unapplied, nonuniform, negative, parentScaled, and sceneMismatch with a clean UI summary + detailed console printout.
🛠️ Safe fixes
- Align Scene Units to profile (does not rescale vertices).
- Apply Scale on Meshes (safe for statics).
- Fix Negative Scales (auto recalculate normals).
- Skip Armature to preserve rigs/skin by default.
📏 Rulers, axis lines, and cages (AABB/OBB)
- AABB or OBB (true extents) with translucent fill & wire.
- On-mesh dimension labels (units + precision), inside the box with adjustable inset.
- Axis colors (X=red, Y=green, Z=blue).
- Draw On Top option for dense scenes.
🔒 Guarded FBX/glTF export Configurable fail-on rules block exports that would break downstream pipelines (toast + JSON-style console report).
🧪 CI / headless validator Run checks in automated builds. Emits JSON to disk and returns non-zero exit codes when violations exist.

Screenshots / GIFs

Demo video (2:05)

🎥 https://youtu.be/iTdByFfPiKs

Quickstart

Pick Target Profile (Unity/Unreal/glTF/CAD)
Run Detection (optional: Selection Only)
Run Fix: align scene units, apply scale, fix mirrored normals; skip armatures if needed
Toggle Ruler Overlay (AABB/OBB, colorize, on-top, precision)
Export (Guarded) → fix any violations → export clean

Installation

Edit → Preferences → Add-ons → Install…
Select the zip (e.g., ais-unit-scale-doctor-0.4.0.zip)
Enable AIS Unit & Scale Doctor
Open 3D View → N-Panel → AIS Tools

Compatibility: Blender 3.0–4.4 (tested 3.6 LTS & 4.4). Windows/macOS/Linux.
Dependencies: none (GPU/BLF fallbacks handled).

Download / Docs / Issues

Download: https://superhivemarket.com/products/unit--scale-doctor
License: MIT (permissive; use in commercial/open projects)

Guarded export (details)

Fail-on rules (comma-sep): negative,nonuniform,parentScaled,unapplied,sceneMismatch
FBX axes set per profile:
- Unity/glTF: Forward -Z, Up Y
- Unreal: Forward X, Up Z
glTF operator enables Y-up flag

On failure: export is blocked; a human-readable toast appears and a JSON-style report is printed to the console.

CI / Headless validation

Example call (write report + exit non-zero on violations):

blender -b --python-expr "import bpy; bpy.ops.preferences.addon_enable(module='ais_unit_scale_doctor')" \
-- --v4-validate --profile UNITY \
--fail-on negative,nonuniform,sceneMismatch \
--out unit_report.json

FAQ

Q: My asset looks mirrored or inside-out after fixing.
A: You likely had negative scale. Enable Fix Negative Scales so normals are recalculated after apply.

Q: Will this break my rigs?
A: By default we skip objects with Armature modifiers. Only freeze rigged meshes when you intend to.

Q: Why do Y/Z labels “swap” when I pick Unity?
A: Unity is Y-up. The overlay remaps axes to your profile so what you see is what the engine expects.

Q: Does Align Scene Units rescale my mesh?
A: No—only scene unit settings change. Vertex data remains unchanged.

Q: Can I use this with CAD millimeters?
A: Yes—select CAD (mm) and validate with rulers before export.

Changelog (0.4.0)

Profile-aware axis remap (Unity Y-up / Unreal Z-up / glTF Y-up export)
AABB/OBB cages with translucent fill and on-top mode
Colorized labels (X/Y/Z) with precision control & inside/inset placement
Expanded detection reasons and parent-scale checks
Guarded FBX/glTF export with customizable fail-on rules
Headless validator (JSON report + exit codes)
GPU/BLF compatibility fallbacks; clean register/unregister

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