Overview#
Edit Form is the command you will use more than any other in the Form environment. It lets you select cage vertices, edges or faces and transform them with a manipulator (move, rotate, scale), which reshapes the smooth surface. Most of the craft in Form modeling is deciding what to select and how to move it.
Where to find it#
- Form tab > Modify > Edit Form.
- Edit Form opens the Form contextual environment tools for moving, rotating and scaling T-spline geometry (Design > Form > Modify > Edit Form).
- Autodesk's help does not list a keyboard shortcut for Edit Form, so none is given here.
Step by step#
Basic move#
- Choose Modify > Edit Form.
- Click a vertex, edge or face on the cage (or a combination). Edit Form shows a manipulator at the selection. Adjacent faces move to maintain continuity.
- Drag one of the arrows to move along a single axis, or a square manipulator to move freely in the XY, XZ or YZ plane.
- Release to commit.
- Click OK to exit the command.
Hold Alt (Option on macOS) while dragging a manipulator to add new geometry as you move. Autodesk calls this one of the most important things Edit Form does. Hold Alt+Ctrl (Option+Command) to keep creases while adding geometry.
Rotate and scale#
- With a selection active, drag a rotate manipulator to rotate about a single axis (X, Y or Z). Make sure the geometry does not twist through itself: self-intersecting faces cannot later be converted to a solid.
- Scale with the other manipulators: the dash scales in a single direction, the corner scales in a plane (XY, XZ or YZ), and the center scales in all directions.
- For precise entries, use the Numerical Inputs fields in the dialog instead of dragging.
Selection techniques#
- Click selects a single element. Hold Ctrl (Cmd on macOS) to select multiple elements.
- Select Through: hidden elements behind other geometry are only selectable with the Select Through option on.
- Loops: double-click an edge to select the loop of edges. Click a face and then double-click an adjacent face to select a loop of faces. Double-clicking a face selects the entire body.
- Selection Options in the Edit Form dialog: Grow/Shrink, Loop Grow/Shrink, Ring Grow/Shrink (selects edges on adjacent faces of the selected edge), Select Next (Alt+arrow keys on Windows), Feature Selection (all faces of a strut or hole), Invert Selection and Range Selection (all faces between two selected faces).
- Selection Filter: Vertex, Edge, Face, All or Body, so you do not pick the wrong thing in a dense area.
Soft selection and proportional editing#
- In the Edit Form dialog, enable Soft Modification.
- Set Extent (Distance, Face Count, or Rectangular Face Count), Transition (Smooth, Linear or Bulge) and Weight. Moving a vertex now also moves nearby control vertices, producing broad, smooth changes.
- Use soft modification for organic bulges and gentle curvature changes; use it off for exact edits.
Options reference#
| Option | What it does | Notes/default |
|---|---|---|
| Transform Mode | Multi (all manipulators), Translation, Rotation or Scale only | Controls which manipulators are shown |
| Coordinate Space | World Space, View Space, Selection Space (group transform) or Local Per Entity | View is handy for sculpting; World for precise axial moves |
| Soft Modification | Moves neighboring control vertices | Extent, Transition (Smooth, Linear, Bulge) and Weight |
| Object Snap | Moves new vertices to the closest point on solid, surface or mesh bodies | Snap Direction: View Space or World Space |
| Numerical Inputs | Type values to move the manipulator | Distance, Angle and Scale fields |
| Selection Filter | Vertex, Edge, Face, All, Body | Limits element type |
| Selection Options | Grow/Shrink, Loop, Ring, Select Next, Feature, Invert, Range | See Selection techniques above |
| Symmetry | Mirrors the edit on the other side | Only active if the body has symmetry set up |
| Freeze | Locks faces or edges | Light blue = frozen; dark blue = automatically locked neighbours |
Tips and pitfalls#
Tip: Edit large to small. First move whole faces and rows of vertices to get the silhouette, then refine with individual vertices. Beginners move single vertices first and end up with lumpy surfaces.
Tip: Switch Coordinate Space to View Space for freehand moves and World Space or Local Per Entity for exact moves. If an axial move mysteriously drifts, you are probably in View space.
Tip: Use the Box display mode (Alt+1) while selecting dense areas, then switch back to Control Frame or Smooth to judge the shape.
Tip: Turn on Object Snap to snap vertices onto a reference solid, surface or mesh body, or position the cage over a Canvas image to match a silhouette. Match from several views, not only one.
Warning: Moving vertices past each other or through the opposite side of the body creates self-intersecting or folded surfaces. These often show up only when you try to finish the form. Use Box display to look for overlapping edges and Repair Body to check for error star points and T points.
Warning: Soft modification can affect elements you did not intend. Freeze the parts you want to protect before using a wide falloff.
Tip: Press Ctrl+Z freely; undo works within the Form session.
Selection strategy in dense cages#
Most Form frustration is a selection problem, not a modelling problem. Four habits help.
- Set the selection filter first. If you want a vertex but keep grabbing faces, switch the filter to Vertices before you click. Switching filter mid-drag is not possible, so decide before you start.
- Use Box or Control Frame display for selecting and Smooth for judging. Autodesk notes that in smooth display mode you edit surface points (the surface points exist to give you something to select), while the control frame is still what changes. Toggle between modes with Alt+1/2/3 rather than working in only one.
- Select by loop, not by element. Double-clicking an edge selects the loop of edges. Moving a loop up 2 mm raises a whole contour line in one go, producing a clean curve where moving 12 single vertices produces a wobble. Loops generally stop at star points, so a loop may be shorter than you expect on a model with detail (general behaviour).
- Select before you scale. Scaling a selection scales about the pivot. Select a ring of vertices around a waist, scale to 85 percent, and the waist narrows evenly. Selecting a single face and scaling shrinks that face toward its own centre instead, which is useful for tapering a limb tip.
Move, rotate and scale: worked numbers#
Suppose you have a 60 mm long Box form with 4 faces along its length and you want a handle that tapers from 30 mm wide at the root to 18 mm at the tip.
- Select the end face and use the Distance field to pull it out 20 mm along its normal axis (World Space or Local Per Entity with the axial arrow).
- Select the end face again and scale it: type 0.6 in the Scale field to bring a 30 mm face down to about 18 mm.
- Select the second ring of vertices from the end and scale to 0.8, so the taper is progressive (30, 24, 18 rather than 30, 30, 18). A stepped taper with one large jump produces a visible kink on the smooth surface.
- If the handle should bend, select the end half of the cage and rotate it by 12 degrees about an axis through the root. Rotating the whole end rather than moving vertices one by one keeps the cross-section shape.
Typing numbers is slower than dragging but is the only way to get symmetric or repeatable results. As a guide, use dragging for shape exploration and typed values once you know what you want.
Soft modification, Freeze and related Modify tools#
The Edit Form dialog is only one of several tools that move cage points. Autodesk's Modify tools reference lists these companions, all useful when plain moving is clumsy.
| Tool | What it does | When to reach for it |
|---|---|---|
| Edit By Curve | Reshapes edges by moving the control points of a driving curve (Degree 1 to 7, Distribution Uniform or Edge Length, Planar Curve, Curve Fit by Control Points or Surface Points) | Adjusting a long silhouette edge with a few handles |
| Smooth | Smooths an area of T-Spline geometry in real time with a smoothing rate | Removing local lumps after heavy editing |
| Cylindrify | Forms uneven features into a smooth cylindrical shape (Auto Feature Selection option) | Regularising a boss, limb or handle |
| Pull | Snaps selected vertices to a target face or surface | Making a form touch a solid body |
| Flatten | Projects vertices to a best-fit or user-defined plane | Creating a flat pad |
| Straighten | Straightens vertices to a best-fit or defined line | Making a straight edge run |
| Freeze / Unfreeze | Locks or unlocks faces or edges | Protecting finished areas before wide edits |
Freeze is the safety net for soft modification: freeze the finished face, edge or area first, then use a large falloff radius on the rest. Frozen areas are protected by light blue (frozen) and dark blue (automatically locked buffer) edges, so the protected shape does not change.
Common failures and fixes#
| Symptom | Cause | Fix |
|---|---|---|
| The manipulator moves a vertex sideways instead of along the axis | Coordinate Space is View Space | Switch to World Space or Local Per Entity |
| A move produces a sharp crease-like fold | You pulled one vertex far past its neighbours | Undo and move the whole ring, or add Soft Modification |
| The surface develops a tiny pinched dimple | A vertex was moved through the surface or two vertices nearly coincide | Weld or move them apart; check in Box view |
| Edits on one side do not appear on the other | Symmetry is not set up, or the element is excluded by Isolate Symmetry | Check the Symmetry panel |
| Selection misses elements at the back | Hidden elements are not selected unless Select Through is on | Enable it or orbit and select from the back |
| You cannot select a frozen face | It is frozen | Run Unfreeze |
Working with reference images#
For product shapes, import a Canvas (Insert > Canvas) on the origin plane, scale it with the Calibrate option using a known dimension, and set opacity to about 40 percent. Then work in orthographic views: pull the cage until the smooth silhouette matches the canvas in the front view, switch to the side canvas, and repeat. Orthographic matching in two views is far more reliable than matching in perspective, because perspective hides depth errors. Match the large forms first (silhouette), then the mid forms (waist, hump), and last the details.
Practice exercise#
Shape a simple mouse-like body and verify it numerically.
- Create a Box 60 x 35 x 20 mm with 4 x 3 x 2 faces and Mirror symmetry across the long centre plane (the plane that splits the width).
- In Control Frame mode, choose Modify > Edit Form. Double-click an edge to select the top front ring and drag the ring down 6 mm to make the front slope.
- Turn on Soft Modification with a radius of about 20 mm and raise the centre of the top by 5 mm to form a hump. Compare with a plain move of the same vertex and note the difference in smoothness.
- Select the bottom face and scale it to 0.8 in the width direction so the body tapers. Check that the body is still symmetric.
- Freeze the bottom face, then use a wide soft modification on the top and confirm the bottom does not move.
- Use Inspect > Measure to read the finished height of the hump from the base. The smooth surface will not reach the cage, so the reading will differ from the cage height; adjust vertices until the measured height is 25 mm.
- Finish Form.
Expected result: a smooth, symmetric mouse-like solid with a front slope, rear hump, tapered base and a measured hump height of about 25 mm. If the sides look flat, move the side vertices outward with soft modification enabled. If one side differs, symmetry was cleared or the edit was made with symmetry suspended.
Related#
- Form primitives
- Creases and edge tools
- Symmetry and patterns