Rebuilding Control Vertices | TutoCAD

Understanding Control Vertices in AutoCAD

Control vertices are essential points that define the shape of NURBS surfaces and splines in AutoCAD. Mastering how to rebuild these control vertices can significantly enhance your modeling capabilities and streamline your design process.

The Need for Rebuilding Control Vertices

As you work with surfaces, you may encounter situations where editing control vertices becomes challenging, especially if there are too many overly complex control points. Rebuilding control vertices allows you to simplify the control points, making it easier to manipulate the shapes while maintaining the overall integrity of your design.

Using the CVREBUILD Command

The CVREBUILD command is a powerful tool in AutoCAD that provides the flexibility to not only modify the number of control vertices in the U and V directions but also to adjust the degree of the surface or curve. This can be particularly useful when you want to reduce complexity or when you need specific geometric properties for your project.

Step-by-Step Guide to Rebuilding Control Vertices

1. Preliminary Setup: Before initiating the rebuild process, ensure that you have an existing NURBS surface or spline that you wish to modify.

2. Attempt to Edit Control Vertices: Select the control vertex you want to move. When you try to manipulate it and receive a warning that editing is not possible, take note of the suggestion: to use the CVREBUILD command.

3. Access the Rebuild Tool:

   • Navigate to the Surface ribbon.
   • Find the Control Vertices panel and click on the Surface – Rebuild option.

4. Select the Surface or Curve: After activating the rebuild tool, you will be prompted to choose the NURBS surface or curve you intend to modify. Click on the desired geometry to proceed.

5. Configure Rebuild Options:

   • The Rebuild Surface dialog will appear, allowing you to customize several parameters.
   • In the Control Vertices Count section, you can specify how many control vertices you want in both the U and V directions to simplify or enhance the surface geometry.
   • Within the Degree section, select a degree value that affects the complexity of each span. Higher values create more intricate surfaces.

6. Additional Options:

   • If you wish to delete the original surface after rebuilding it, check the Delete original geometry box. If you want to keep the original surface, leave it unchecked.
   • If applicable, check the Retrim previously trimmed surfaces option to maintain any trims on surfaces that had been modified before.

7. Check Maximum Deviation: The dialog also displays the Maximum Deviation, an important measure that indicates how closely the new surface will adhere to the original.

8. Finalizing Changes: Once you have adjusted the settings to your satisfaction, click OK. The control vertices will automatically update based on your specifications, and you will see the changes reflected in the modified surface.

Frequently Asked Questions

1. What is the purpose of rebuilding control vertices?
Rebuilding control vertices simplifies the geometry of surfaces or curves, making editing and manipulation easier while retaining the desired shape of the design.

2. How does changing the degree affect my surface?
Changing the degree affects the smoothness and complexity of the surface. Higher degree values increase the number of control points per span, resulting in a more refined and intricate surface.

3. Can I undo the rebuild if I’m not satisfied with the results?
Yes, as with most commands in AutoCAD, you can use the Undo feature (Ctrl + Z) to revert the changes made by the rebuild command if you find the results unsatisfactory.