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Split

The Split tool (also known as Separate) detects disconnected shell components within a surface and separates them into individual surface objects. This is particularly useful for isolating distinct anatomical structures that were segmented together, or for extracting the largest meaningful components from a noisy surface.

Medical Disclaimer

This tool is provided for research and educational purposes only. Any clinical or diagnostic use requires proper validation in accordance with applicable regulations.

Overview​

A single surface object can contain multiple disconnected shells—separate mesh components that share no vertices or edges. This commonly occurs when:

  • Multiple anatomical structures are captured in a single segmentation mask
  • Noise in the imaging data creates small disconnected artifacts
  • A surface is imported from an external source with multiple components

The Split tool analyzes the surface connectivity and creates individual surface objects for each shell, allowing you to work with them independently.

Interface​

Active Surface Information​

FieldDescription
Connected shellsThe number of disconnected shell components detected in the active surface

This value updates automatically when you activate a different surface or when the surface data changes.

Separate Only the Largest Shells​

When enabled, you can limit the split operation to extract only a specified number of the largest shells (by surface area). This is useful for:

  • Extracting only the main anatomical structure while discarding noise
  • Separating the N largest components from a complex surface
  • Quickly isolating significant structures
ParameterDescriptionDefault
Largest shellsNumber of largest shells to extract (by area)1

When disabled, all shells are separated into individual surface objects.

Options​

OptionDescriptionDefault
Remove active surfaceDelete the original surface after successful splitDisabled

Actions​

ButtonDescription
ApplyPerform the split operation
note

The Apply button is only enabled when the active surface contains more than one connected shell.

Typical Workflows​

Isolating the Main Structure​

When your surface contains a primary structure with small noise artifacts:

  1. Activate the surface to split
  2. Enable Separate only the largest shells based on their area
  3. Set Largest shells to 1 to extract only the main structure
  4. Enable Remove active surface if you don't need the original
  5. Click Apply

The result is a single surface object containing only the largest connected component.

Separating All Components​

To create individual surface objects for every disconnected shell:

  1. Activate the surface to split
  2. Disable Separate only the largest shells based on their area
  3. Click Apply

Each shell becomes a separate surface object in the object tree.

Extracting Multiple Structures​

To extract a specific number of the largest structures (e.g., the 3 largest bones):

  1. Activate the surface
  2. Enable Separate only the largest shells based on their area
  3. Set Largest shells to the desired number (e.g., 3)
  4. Click Apply

This creates separate surface objects for each of the N largest shells, discarding smaller components.

Split vs. Filter Shells​

Both tools work with disconnected shells, but they serve different purposes:

ScenarioUse SplitUse Filter Shells
Create separate surface objects for shells✓
Keep shells in a single surface but remove unwanted ones✓
Extract the N largest structures as separate objects✓
Remove noise shells while keeping everything in one object✓
Need detailed shell statistics (volume, area, triangles)✓

Split creates new surface objects for the extracted shells.

Filter Shells modifies the existing surface by removing unwanted shells.

Best Practices​

  1. Check shell count first: Review the Connected shells count before splitting. If the number is unexpectedly high, your surface may contain many noise artifacts.

  2. Use Filter Shells for cleanup: If you have many small noise shells, consider using Filter Shells first to clean the surface, then use Split if you still need to separate components.

  3. Consider the naming: After splitting, rename the resulting surface objects to identify their content clearly.

  4. Enable Remove active surface cautiously: Only enable this option when you're confident you don't need the original composite surface.

  5. Run diagnostics after splitting: Individual shells may have different quality characteristics. Use Diagnostics and Fixes to verify each shell's quality.

Understanding Shell Size​

The "largest" shells are determined by surface area, not volume. This is important because:

  • A hollow structure may have a large surface area but small enclosed volume
  • Thin, elongated structures may have smaller areas than compact structures of similar volume

If you need to filter or separate shells by volume, use the Filter Shells tool, which offers volume-based filtering options.

See Also​