Manually Placed Seams

Flatiron allows you to preserve manually defined seams during the unwrapping process.

By default, Flatiron generates its own seams to achieve optimal results. However, you can choose to reuse existing seams from a source map channel.

Keep Seams Option

Disabled
Flatiron discards all existing seams and generates a new seam layout based on the current settings.
Enabled
Flatiron uses the existing seams from the selected source map channel to unwrap the meshes.

Stretch vs. Seam Placement

Manually placed seams and the defined stretch limit may conflict.

If the existing seams do not allow Flatiron to maintain the specified stretch constraint, the algorithm will automatically introduce additional seams.

You can resolve this by:

Adding more seams manually
Increasing the allowed stretch value

Stretch Behavior

Stretch = 1.0
Flatiron prioritizes your manual seams and avoids adding new cuts whenever possible, even if this results in high distortion.
Low stretch values
Flatiron enforces stricter distortion limits and will introduce more seams to maintain surface quality.

Finding the right balance between seam placement and stretch is essential and depends on how the UV map will be used downstream.

Seam Optimization

Flatiron may remove manually placed seams if they are considered redundant.

This typically happens when:

A seam does not fully separate UV charts
Adjacent surfaces can be placed without distortion

In such cases, the seam is removed to avoid unnecessary padding and improve packing efficiency.

Polygonal Unwrapping Mode

When using polygonal unwrapping:

Manually placed seams that split polygons internally are preserved
Automatically generated seams will respect polygon boundaries and will not further split polygons

This ensures consistency with the polygonal constraint while still honoring manual input where possible.

Flatiron Modifier Texture Baking Modes