Rhino 8 CageEdit Guide: Smooth, Controlled Model Deformation

Rhino 8’s CageEdit command lets you change the shape of captive objects by editing the points of a control cage. In the workflow described in McNeel’s Rhino 8 help documentation, you first select the objects to edit, then specify or create a control object; edits to the cage points are applied to the geometry. The command can affect an entire object or be used to target a specific region. This guide covers the basic steps and the options that influence the result.

What does CageEdit do?

CageEdit uses a control object defined around or on the object being edited. Moving the cage points translates into changes to the model’s shape. Rhino’s documentation also notes that control points on curves, surfaces, and meshes can be selected as objects to edit. The command supports both global and local deformations, allowing you to try changes at different scopes.

You can create a control object with the Cage command, or select an existing surface or curve for this purpose. The Cage command creates a box-shaped cage based on the selected objects. When creating a cage from a bounding box, the control object can be a line, a planar shape, or a three-dimensional cage. To use the object itself as the control, select one of its edges or a face of a polysurface. The documentation also notes that CageEdit deformation does not separate polysurface geometry at its seam edges.

Cage deformation in Rhino 8: step by step

1. Select the geometry to edit. Before starting CageEdit, select the objects whose shape you want to change. You can also select control points on curve, surface, or mesh objects.

2. Specify the control cage. Open CageEdit via Transform › Cage Editing › Cage Edit. To use a ready-made cage, run the Cage command via Transform › Cage Editing › Create Cage. With Cage, select the objects and press Enter, then draw the cage box. In the CageEdit workflow, you select the objects to edit, specify the control object, and edit the cage points.

3. Adjust the cage shape and point distribution. The BoundingBox option positions the cage relative to the object’s bounding box. You can set the number and degree of points for the directions of a line-, rectangle-, or box-shaped control object. When you enter a number at the Cage parameters prompt, the same number of points is used in the directions of the rectangle or box, and the degree options are adjusted accordingly. The documentation does not recommend an ideal number of points for all models, so choose based on the geometry and the intended deformation.

4. Edit the control points. Change the shape of the cage by moving its points. Clicking a control polygon selects two adjacent cage points; double-clicking a polygon selects a row of points. This behavior can help when selecting points that need to be edited together.

5. Consider the accuracy and surface structure options. Accurate can slow updates and may produce denser surfaces in refitted objects. Fast creates surfaces with fewer control points, but accuracy may be lower. If you need to preserve the curve or surface’s control-point structure, you can set PreserveStructure=Yes. However, if the object does not have enough control points, the result may be less accurate. With PreserveStructure=No, Rhino may refit the object as needed for an accurate deformation. This setting does not apply to polysurfaces.

Region of influence and object behavior

The Region to edit setting is the key choice for determining which part of the scene is affected by the deformation. When set to Global, the control object’s influence is not limited to the area inside the cage. Objects that are partly outside the cage may also change, and the effect on geometry farther from the control object may become noticeable. So unless you intend to make a broad change, check the other objects around the cage.

With the Local approach, you define a Falloff distance around the control object. Objects—or parts of objects—beyond this distance are unaffected by the deformation. This lets you limit the edit while creating a transition between the area of full influence and the region that remains unchanged. To further confine the effect to a defined area within the surrounding volume, you can specify a sphere, cylinder, or box under the Other option; you also enter a Falloff distance for this use.

The Rigid option is used to move objects without stretching their shape. Since the setting works on a per-object basis, different objects captured by the same control object can have different rigid behavior. To change this behavior for an object, it must be captured again with the same control object. Objects in a group transform together. Block instances, regardless of the Rigid setting, transform rigidly while retaining their shape.

Using CageEdit in architectural, interior design, and visualization workflows

Architects and interior designers can use CageEdit to explore controlled alternatives to a massing or surface shape. This is a suggested use based on the command’s documented functionality; the documentation does not describe specific architectural scenarios or guarantee particular results. McNeel notes that a small number of cage control points can modify more complex objects and provide smoother transitions than standard control-point editing. Even so, the same cage setup may not suit every piece of geometry.

For visualization teams, the choice comes down to balancing update speed against surface accuracy. Fast may be worth considering for quick shape studies, while Accurate can be tried when a more accurate deformation is needed. Since these settings can produce different surface results, it is sensible to review them on the model before using them in a final file. The documentation does not provide specific hardware requirements, performance measurements, licensing terms, or pricing, so no further assumptions should be made on these points.

Common mistakes

• Assuming Global only affects geometry inside the cage: Objects outside the cage may also change with this setting. If you need a more limited region, consider Local and Falloff distance.

• Expecting the highest surface accuracy from Fast: Fast creates surfaces with fewer control points, and accuracy may be lower.

• Assuming PreserveStructure=Yes will give the same result on every model: Too few control points can reduce deformation accuracy.

• Assuming block instances will change shape: Block instances always transform rigidly in CageEdit.

CageEdit history is built into the command, regardless of whether the History setting is on. You can use ExtractOriginalCaptives to obtain the original shape at its initial position without changing the deformed object. Use ReleaseFromCage to remove objects from the cage’s influence. The Explode command converts the control object into regular geometry, so keep this in mind if you need to continue working with it.