# Passive Spacing

*Passive spacing provides indirect control over mesh behavior without explicit refinement specification, enabling smooth transitions between different mesh regions and maintaining mesh continuity across interfaces.*

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## Available Options

| *Option* | *Description*                  |
|------------|------------------------------|
| **Type** | Spacing control methodology |
| **Assigned surfaces** | Target surfaces for spacing control |

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## Detailed Descriptions

### Type

*Specifies the methodology for spacing control.*

- **Required**
- **Available options:** 
  - `projected`: Projects spacing from adjacent volumes.
  - `unchanged`: Preserves existing surface mesh.
>**Note:** Selection determines how mesh spacing is controlled.

### Assigned surfaces

*Identifies the surfaces where spacing control will be applied.*

- **Required**
>**Notes:** 
>  - Must reference valid surface entities in the geometry. 
>  - Assign the boundaries by selecting from the list using the + button or select graphically in the viewer region.

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<details>
<summary><h3 style="display:inline-block"> 💡 Tips</h3></summary>

- Use projected spacing for interface regions between different mesh zones
- Apply unchanged spacing where surface mesh quality is already optimal
- Consider geometric complexity when selecting spacing type
- Ensure compatibility with adjacent refinement regions
- Balance mesh quality with computational efficiency

</details>

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<details>
<summary><h3 style="display:inline-block"> ❓ Frequently Asked Questions</h3></summary>

- **When should I use projected vs. unchanged spacing?**  
  > Use projected for interface regions requiring smooth transitions, and unchanged when existing surface mesh quality is satisfactory.

- **How does passive spacing interact with other refinements?**  
  > Passive spacing operates independently of other refinements, focusing on maintaining mesh continuity and quality.

</details>

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<details>
<summary><h3 style="display:inline-block"> 🐍 Python Example Usage</h3></summary>

```python
from flow360 import PassiveSpacing

# Projected spacing for interface region
interface_spacing = PassiveSpacing(
    name="interface_region",
    type="projected",
    faces=[interface_surface]
)

# Unchanged spacing for optimized surface
preserved_spacing = PassiveSpacing(
    name="optimized_surface",
    type="unchanged",
    faces=[optimized_surface]
)
```
</details>