> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ntop.com/llms.txt
> Use this file to discover all available pages before exploring further.

# How to Create Advanced Swept Surfaces with Conic and Cubic Bezier Sections

## **Objective:**

This article explains how to generate advanced swept surfaces between two rail curves using a spine curve. By utilizing the **Conic Section Sweep**, **Conic Section Sweep by Tangent**, and **Cubic Bezier Section Sweep** blocks, you can create high-fidelity aerodynamic profiles and smooth transitions for complex modeling workflows

## **Applies to:**

* Surfacing
* Workflows: Aerodynamics, Fluid Flow Management, Architectural Design

## **Procedure:**

### 1. Prepare Your Curves

Before using the sweep blocks, ensure you have the following curve inputs prepared:

* **Rail 1 and Rail 2:** These define the outer boundaries of the sweep. Note that these cannot be closed curves.
* **Spine:** This curve acts as the origin or axis for the sweep operation.

### 2. Select the Appropriate Sweep Block

Choose the block that best fits your design requirements:

* **Standard Control:** Use **Conic Section Sweep**.

  * This creates a swept conic section where the resulting geometry extends beyond the rails along the spine's tangents.
  * Use this for when Rails that are planar and orthogonal

![](https://files.learn.ntop.com/help-articles/implicit-modeling/50598706877075.png)- **Tangency Control:** Use **Conic Section Sweep by Tangent**.

* Select this when you need precise control over the surface tangency to strictly define the "take-off" angle of the surface from the rails.
* This block accepts tangent vector fields at each rail.
* Use this when you want a conic (no inflection points) and control over tangents

![](https://files.learn.ntop.com/help-articles/implicit-modeling/50598706905875.png)- **Curvature and Smoothness Control:** Use **Cubic Bezier Section Sweep**.

* Select this for high-fidelity control over surface continuity.
* This block uses spatially varying tangent vector fields and magnitude fields at each rail to control smoothness.

![](https://files.learn.ntop.com/help-articles/implicit-modeling/50598722152595.png)### 3. Configure the Shape Parameters (Rho)

For the conic sweep blocks, the cross-sectional shape is defined by the **Rho** value. You can define this as a constant value or use a **Ramp** block to vary the shape spatially along the sweep.

![](https://files.learn.ntop.com/help-articles/implicit-modeling/50598706934803.png)

<Card>
  <table> <colgroup> <col /> <col /> <col /> </colgroup> <tbody> <tr> <td><p><strong>Rho Value</strong></p></td> <td><p><strong>Resulting Curve Type</strong></p></td> <td><p><strong>Example</strong></p></td> </tr> <tr> <td>ρ\<0.5</td> <td>Ellipse</td> <td>  <img src="https://files.learn.ntop.com/help-articles/implicit-modeling/50598722191379.png" /></td> </tr> <tr> <td>ρ=0.5</td> <td>Parabola</td> <td>  <img src="https://files.learn.ntop.com/help-articles/implicit-modeling/50598706992787.png" /></td> </tr> <tr> <td>ρ>0.5</td> <td>Hyperbola</td> <td>  <img src="https://files.learn.ntop.com/help-articles/implicit-modeling/50598707018131.png" /></td> </tr> </tbody> </table>
</Card>

### 4. Adjust Tangency (Optional)

If using the **Cubic Bezier Section Sweep**:

* Adjust the **Tangent Magnitude** inputs.
* Note that these values are relative to the in-plane distance between the rails.
* A value of 1.0 indicates that the handle length equals the distance between the rails at that specific point.

### 5. Finalize the Body

The output of these blocks is an implicit surface. To create a solid, closed body suitable for downstream operations:

* Use the **Boolean Intersect** block to close the surfaces.

## Best Practices and Troubleshooting

**Angle Thresholds**

* **Avoid Steep Angles:** We recommend avoiding steep angles between the rail curves and the spine. This prevents unexpected results during shelling or offsetting downstream.

![](https://files.learn.ntop.com/help-articles/implicit-modeling/50598707053587.png)

* **Rule of Thumb:** Maintain an angle threshold between 45° and 60°.

**Common Errors**

* **"Rays from the axis..." Error:** This indicates that the rails are perpendicular to the spine at some point. Rails cannot be perpendicular to the spine. Ensure that rays projected from the axis along the specified direction intersect the curve only once.
* **"Improperly configured inputs" Error:** This often indicates that the geometry is self-intersecting relative to the axis.
* **Closed Rails:** Ensure Rail 1 and Rail 2 are open curves. If they are closed, replace them with open curves to resolve the error.

## Download Example File

Download the example file to explore lofting by section sweep:

[Lofting by Section Sweep](https://files.learn.ntop.com/Support%20Article%20Example%20Files/Knowledge%20Base/Implicit%20Modeling/section_sweep_example.ntop)

## Keywords:

*Conic Section Sweep Advanced Swept Surfaces Aerodynamics Conic Section Sweep by Tangent Cubic Bezier Section Sweep Surfacing*