Rhino 8 CageEdit Guide: Controlled Model Deformation with a Cage

In McNeel’s help documentation, CageEdit in Rhino 8 is described as a deformation tool in which the control object defines the area to be edited. After selecting the objects to edit, users create a cage or define a suitable existing surface or curve, then reshape the geometry by moving the control object’s points. The tool supports both broad changes and edits that affect only part of an object.

1. Start a cage edit

First, select the objects to modify. Rhino documentation calls these “captive” objects. Control points on a curve, surface, or mesh can also be used as the items to edit. The control object can be created with the Cage command or selected as an existing surface or curve. To use an object as its own control object, you can use one of its edges, or one of its faces if it is a polysurface.

Rhino 8 Help lists the menu path for CageEdit as Transform › Cage Editing › Cage Edit, and the path for creating a cage as Transform › Cage Editing › Create Cage. The creation command prepares a box-shaped cage, which can then be attached to objects with CageEdit and edited via its control points.

Cage

The basic workflow is:

1. Select the objects to edit.

2. Create a new control object or specify an existing curve or surface.

3. Change the objects’ shape by editing the control cage’s points.

Clicking once on a cage control polygon selects two neighboring cage points; double-clicking selects a row of points. The source notes that cages with a small number of control points can also be used on complex objects and may help produce smoother transitions. You may not need a dense cage for every model, but the documentation does not specify an ideal number of points.

2. Choose the cage type and structure

The control object can be created as a line, rectangle, or three-dimensional box, based on the bounds of the input geometry. The BoundingBox option determines the box’s position relative to the object’s bounding box. For two-dimensional objects, ObjectPlane aligns the rectangular cage with the object’s plane in 3D space.

PointCount sets the number of cage control points in each direction. Degree sets the degree in the corresponding direction of a line, rectangular, or box cage. If you enter a single number at the “Cage parameters” prompt, that number is applied to every direction, and the degree options are adjusted accordingly. Since the source does not recommend a preset point count, test values based on the model’s shape and the level of control required.

PreserveStructure does not apply to polysurfaces, so the option is not shown when only polysurfaces are selected. Rigid works on a per-object basis. The same control object can affect some objects rigidly and reshape others. To change the rigidity setting later, recapture the objects with the same control object. Grouped objects transform as a single unit. Block instances transform rigidly regardless of the Rigid setting.

3. Manage local influence and deformation quality

With the Global option, the area where the cage touches the object is not treated as the limit of its influence. Objects that fall only partly within the cage can also be affected by the transformation. The effect can also increase in areas far from the control object, so check for unintended changes when working with a large model.

When using Local, Falloff distance defines the area of influence near the control object. Deformation can be applied fully inside the cage or within the region defined by line and rectangular control objects. Parts outside this area remain fixed, while the effect gradually diminishes in the region between. You can also further limit the spatial influence of the control object with a sphere, cylinder, or box.

When choosing between Accurate and Fast, consider more than processing speed. Accurate can slow updates and may rebuild the surface with a denser structure. Fast uses a simpler control-point structure, but deformation detail may be lower. PreserveStructure=Yes retains the existing structure, but if the object does not have enough control points, shape changes may be less precise. The No option allows refitting with additional control points when needed.

CageEdit creates history regardless of the History setting. Rhino 8 also adds ExtractOriginalCaptives, which restores the undeformed originals of objects attached to a selected control cage to their initial positions; objects that have been deformed are unaffected.

ExtractOriginalCaptives

To detach an object from the influence of a control object, use the ReleaseFromCage command. It removes selected objects from the influence of the CageEdit control.

ReleaseFromCage

Use in architecture and visualization workflows

CageEdit is well suited to reshaping a larger area via a cage when controlled changes to a mass or surface are needed, rather than editing individual geometry points one by one. The Local option supports working on a specific area without affecting the entire model. The Rigid setting can also be used to change the position of elements whose shape must be preserved. The fact that polysurface joins are not separated during CageEdit is a notable behavior when working with this type of geometry.

It is useful to test on a small scale before editing an important model, particularly to check the limits of Global influence and Falloff distance. Rhino 8 documentation does not specify hardware requirements, pricing, or licensing terms for CageEdit, so no particular advantage or requirement should be assumed in these areas. Before using it, verify the version of the installed software and your organization’s licensing terms separately.

Common mistakes

• Using Global when you expect a local change; this option can also affect areas outside the cage.

• Treating Fast as the mode that provides the highest detail; the source notes that it produces surfaces with fewer control points.

• Looking for PreserveStructure on a polysurface; the option is not shown for this geometry type.

• Expecting block instances to change shape; they transform rigidly regardless of the Rigid setting.

• Applying a fixed PointCount or Degree value to every model when the documentation does not recommend one.