Optimizing Model Scale For Automatic Rigging Success In Blender

What is Model Scale and Why It Matters for Rigging

Model scale refers to the size of a 3D model relative to the default grid in Blender’s scene. It is a crucial consideration when preparing models for automatic rigging because inconsistent scales can cause the armature, bones, and weights to generate incorrectly. Setting an appropriate scale before rigging ensures properly sized and proportional deformation bones, optimal bone heat zones, efficient weighting, and avoids tedious fixes to scale issues down the line.

For optimal auto-rigging results, models should have a consistent scale across all objects and parts. A human character model, for example, is best scaled to real-life human dimensions. Accessory models like hats, weapons, or backpacks should match the same scale. Environment models, vehicles, and scene props can share a scaled-up or scaled-down size as needed. Inconsistency can manifest as spindly, malformed, or oversized deform bones, skewed envelopes, distorted deformations, disconnected vertices, and stretching during animations.

Common scale-related failures and issues when attempting automatic rigging include: misaligned joints and bones missing parts of the mesh, uneven weighting and deformation between body parts, unreliable physics simulation, animation glitches like models sinking into the ground plane, broken rigging set-ups when appending or linking scaled assets, and inability to reuse existing animations or motion capture data across different scaled models.

Ideal Model Scale Range

For biped organic characters that need to deform realistically, the recommended model height is between 180 to 250 cm, or around the average human adult height range. This allows enough geometry density to support quality deformations and easier re-use of motion capture animations. For background characters, heights between 100 to 400 cm are often suitable.

When modeling assets, it helps to visualize real-world sizes early on instead of staying with the default grid scale. Simple objects can be scaled to metric dimensions, while complex assemblies and scenes may need scaled-up sizes. As long as the scale stays consistent across interconnecting parts and linked objects, the absolute scale can be customized as needed.

In some situations, models require resizing before satisfactory automatic rigging is possible. Overly complex models may need to be upsized for rig stability. Models with insufficient geometry density can be scaled up to improve deformation quality. Models much larger or smaller than the ideal height range may need to be scaled down or up correspondingly prior to rigging.

Preparing Models for Automatic Rigging

Blender allows scaling objects visually in the 3D Viewport, but also provides precise scale controls in the Object Properties panel. For reliable rigging, it is best to set scale deliberately through the Object Properties than just visually. The scale can be set independently for each axis as needed.

The Apply > Scale transform function permanently commits any existing scale changes to the model geometry itself. This can fix issues if rigging fails or deformations glitch due to residual scales on parts. Apply > Scale should be done just before generating the armature.

As a check, enable the Measureit plugin’s display tools like rulers, protractors and calipers. The measured dimensions should match expected real-world sizes. If not, additional scaling fixes may be needed before rigging. The plugin also helps spot inconsistent scales across model parts early.

Fixing Models with Bad Scale

Models with bad scale typically run into errors when attempting automatic rigging in Blender. Visual glitches like skewed envelope deformations, twisting joints and disconnected vertex groups indicate fundamental issues with model proportions.

To troubleshoot, first check if any object parts have unapplied scales by selecting each part and examining its Object Properties scale values in the N-panel. A non-uniform scale on certain body parts can cause rigging and skinning distortions easily.

Extremely small or large scale values likewise cause glitches. The Measurement tool can quickly compare sizes across parts – if there is more than 10x difference, their scales likely need fixing.

Once problem scales are identified and corrected, use Apply > Scale to commit these changes before re-doing any auto-rigging. Maintaining good topology also helps avoid issues – bad topology contributes to poor skinning and deformation.

Example Model Scales for Rigging

Custom Python scripts allow batch scaling multiple models easily prior to rigging and animation. This snippet scales selected models to real-world human dimensions. The models should already have good topology and cleaned up geometry:

import bpy
from mathutils import Vector

selected = bpy.context.selected_objects

for obj in selected:
  dim = obj.dimensions
  scale_factor = 1.8/dim.y
  
  obj.scale = Vector((scale_factor, scale_factor, scale_factor))

For a human character model intended as main character, it is recommended to scale it precisely to 180-200 cm in height. Maintain this height then assemble and scale all related accessories, clothing, hair and props to this rigid size for animation scene consistency.

Secondary background human models can vary more in heights between 100 cm to 400 cm as artistic needs dictate. Just ensure the scale stays vertically uniform if extreme heights are used.

Consistent Scale for Efficient Animation

Consistency in model scale is critical because it directly impacts animation efficiency. Motions and poses can only be reused reliably across similarly sized, scaled rigs. Physics simulation also behaves more predictably with controlled scales between dynamic props and colliders.

Artists should model primary scene elements and modular assets with their eventual end usage and animation context in mind. Standardized scales that match the final environment and main characters vastly simplify the animation process. Dynamically linking in modular scene assets already built to consistent scale removes guesswork.

When appending or linking model, armature and animation data from other files or asset libraries into a scene, it is vital they share the same base scale as existing objects for linking to succeed. Failure to establish matching scales beforehand results in broken, disconnected rigs and missingasset references.