Trim

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Geometry Fix
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Edit

Trim

Ctrl (CMD) + T

The Trim command cuts and deletes selected portions of an object at the intersection with another object.

Cutting object

Object to trim
  • Curve
  • Surface/Polysurface
  • Curve
  • Surface/Polysurface
  • Hatch

Steps

  1. Select the cutting objects.
  2. Select the parts of objects to trim away.
    Or
    Press Shift to extend objects to the trimming object.
  • Hatches can be trimmed.
  • Holes in hatches can be removed by the UntrimAll command.
Command-line options
IP

Type IP for InfinitePlane options.

SubCrv

Type subcrv to select part of a curve as input.

ExtendCuttingLines

Imaginary extensions of the line are used. This makes it unnecessary to manually extend lines that do not intersect the objects to trim.

ApparentIntersections

Determines whether or not curves are trimmed in relation to the view. They do not need to intersect in 3-D space. They only need to appear to intersect in the active viewport.

This option does not apply to surfaces.

Note

  • If it is difficult to select the parts to trim off, use the Split command and then delete the unwanted parts.
  • Use the Untrim command to remove a trimming boundary from a surface.
  • When trimming a surface with a curve in a plan parallel view like the default Top, Front, and Right view, the cutting curve is projected on the surface in the view direction.
  • When trimming a surface with a planar curve in an angled parallel or a perspective view like the default Perspective view, the cutting curve is projected on the surface in a direction perpendicular to the curve plane.
  • When trimming a surface with a 3-D curve in an angled parallel or a perspective view, the cutting curve is pulled on the surface by closest points.

Line

Draw a temporary line to use for the cutting object.

Trimmed Surfaces

A trimmed surface has two parts: a surface that underlies everything that defines the geometric shape, and trimming curves that either trim away the outside portion of the surface or cut holes in its interior.

Those trimming curves exist on the underlying surface. The underlying surface may be larger than the trim curves, but you won't see the underlying surface because Rhino doesn't draw anything for the part of the surface that is outside the trim curves.

Only the underlying surface defines the actual geometry of the shape. The trim curves do not define a surface -- they only mark which part of the surface is to be considered trimmed away.

If you have a trim curve that runs diagonally across a surface, the trim curve itself doesn't have any real relationship to the control-point structure of the surface. You can see this if you select such a trimmed surface and turn its control points on. You'll see the control points for the whole underlying surface, which doesn't necessarily have any connection with the trim curves.

You can remove the trim curves and get back to the underlying surface using the Untrim commands to remove holes or outside boundaries.

When you have a trimmed surface whose underlying surface is much larger than the outside trimming boundary, you can use the ShrinkTrimmedSrf command to shrink the surface back so that it is only large enough to hold the trimming boundaries and doesn't have a large extra unused area.

Related commands

Untrim

Toolbar Menu

Geometry Fix
Surface Tools

Curve Drawing
Geometry Fix
Main
Main1
Solids Sidebar
Surface Sidebar

Surface

Surface Edit Tools >

Untrim

Detach Trim

The Untrim command removes trim curves and surfaces joined at trim curves from a surface.

 Crease splitting enabled

Steps

  • Select the edge boundary of a trimmed surface.
Command-line options

KeepTrimObjects

Determines whether or not the original trimming objects and joined geometry are separated and retained or deleted.


KeepTrimObjects=Yes (left); KeepTrimObjects=No (right).

AllSimilar

In the image above, the surface boundary consists of trimmed (red) and untrimmed (blue) edges. Holes are trimmed edges (green) that do not touch the boundary.

Yes
  • Clicking on (a) untrims all red edges.
  • Clicking on (b) untrims all holes.
No
  • Clicking on (a) only untrims the connected red edges.
    The red edges on the opposite side are retained.
  • Clicking on (b) only untrims the hole.

ReplaceEdge

Toolbar Menu

Surface Tools

Surface

Edge Tools >

Replace Edge

The ReplaceEdge command re-trims the selected trimmed surface edge with a line, extensions of the adjacent edges, or a curve.

Steps

  • Select surface edges to delete.
Command-line options

KeepTrimObjects

Determines whether or not the original trimming objects are retained.

Mode
ReplaceWithLine

Replace the edge with a line between the edge end points.

ExtendSideEdges

The two surrounding edges extend.

The edges must meet within surface boundary to give successful results.

SelectCurve

Edges will be replaced using the selected curve to retrim.

UntrimAll

Toolbar Menu

Not on toolbars.

Surface

Surface Edit Tools >

Untrim All

Detach All

 Crease splitting enabled

The UntrimAll command untrims interior (holes) and exterior trims on the selected surfaces all at once.

  • Holes in hatches can be removed by the UntrimAll command.

UntrimBorder

Toolbar Menu

Not on toolbars.

Surface

Surface Edit Tools >

Untrim Border

Detach Border

The UntrimBorder command untrims all exterior trims of the selected surfaces. Interior trims (holes) will remain.

UntrimHoles

Toolbar Menu

Holes

Solid Tools

Surface

Surface Edit Tools >

Detach Holes

Untrim Holes

Solid

Solid Edit Tools > Holes >

Delete Hole

The UntrimHoles command untrims selected holes (interior trims) that do not touch surface borders. All=Yes untrims holes on the selected surfaces all at once.

  • This command also untrims the holes in polysurfaces.

Command-line option

All
Yes

Deletes all holes on the selected surfaces.

No

Lets you pick the holes you want to delete.

MaximumEdgeLength

Holes with edges at or smaller than this value can be deleted, either one-by-one or all at once, according to the command line setting for All=Yes/No. Type a maximum edge length number, or pick an existing hole edge to set the length.

KeepTrimObjects

Determines whether or not the original trimming objects are retained.

See also

Split and trim curves and surfaces