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Joins together curves into longer single curves, or joins surfaces along common edges into solids.

Surfaces will only be joined at common unattached edges. If you need to combine 2 objects that will require some kind of intersection and pieces removed during the combining process, then use the Boolean Union command instead.

Surface edges must be within 0.005 units from one another to be joined.


Breaks joined objects into individual separate objects. Curves will break up into individual segments; for example, a rectangle will convert into 4 separate line objects. A solid will break up into individual faces; for example, a box will separate out into 6 plane objects.

If a solid has face sub-objects selected, just those selected faces will be extracted from the solid. This allows for extracting just one particular sub-assembly from a larger solid.


Cuts up an object. Some portions may be removed to make holes, or optionally all sliced up pieces may be retained.

Trim works on curves, surfaces, or solids. The general procedure is to first select the object to be trimmed, and then run the Trim command. Next select the cutting objects, then select which pieces to discard. If you want to keep all the pieces instead of discarding any, then click Done (or right-click in a viewport) without selecting anything at that final stage.

Sometimes if you want to remove a lot of pieces, it can be easier to select the items you want to keep instead of the portions to discard. This can be controlled by switching the Mode: option to Mode: Keep.

When trimming curves, it is possible to add cuts to the curve at specific points by clicking the "Add trim points" button. For example, if you want to split a line at its midpoint, select the line, run Trim, click "Add trim points" and then click a point at the midpoint of the line and click Done. This will split the line at that point. It is also possible to trim a curve by selecting point objects as the cutting objects.

It is not necessary to project curves on to surfaces before trimming. Trimming already includes projection built in, so just use the curve as a cutting object directly.

If 2 objects intersect one another and you want to cut each of them with the other, then select both of them, run Trim, and then click Done at the prompt for selecting cutting objects. This is called a "mutual trim" operation, it will use those objects as both sources and cutters.

Trim will slice just the outside surface skin of a solid. If you want to make cuts through an object where it stays as a solid, use the Boolean operations instead of Trim.

You can also use Trim on surface edges to split the edges into smaller separate segments. The Merge command can be used to reverse this and glue split edges into longer single edges.


Extend a curve to meet the selected boundary objects. The boundary objects can be curves, surfaces, or solids. Currently only curves are supported as the object to be extended.

Lines and curves will be extended by a straight line. Arcs will be extended as arcs.

Example for extending curves to a boundary:

It is also possible to extend 2 curves to meet each other instead of meeting a single boundary. This is called mutual extend, and can be activated by selecting both curves, running Extend, and then clicking Done instead of choosing a boundary object.

Example of mutual extend mode:

Show pts

Turns edit points on or off.

You can also use the Esc key to turn points off, see Shortcut keys for more information.

When a curve has control points turned on, an additional edit mode is enabled if you click and drag on the body of an unselected curve. This enables "drag point on curve" mode where the curve will be deformed to pass through the point you dragged on. This works by moving several nearby control points in one single action, so it can be useful for roughing out the shape of the curve.

Curves and individual surfaces can always have points turned on. Solids made up of surfaces joined together at common edges can only have points turned on if all the surfaces share the same points along the common edge. If 2 joined surfaces have different structures along a joined edge, points cannot be turned on for that object because it would be easy to pull the surfaces apart and ruin the shared edge. In this situation it is possible to use Edit/Separate to break the joined object into multiple independent surfaces and you can turn on points for the individual surfaces.

Add pt

Adds a new point to a curve.

You can make a point that will form a sharp corner when it is moved by checking the "Make corner point" option, or holding down Ctrl when clicking.

To add many points, enable the Repeat checkbox, or right-click to repeat the last command.

There are 2 different methods for adding points. If points for the curve are turned on and you click on the dashed hull between 2 existing points, a new point will be added with the same effect as if you had drawn the curve with that additional point. Other points will stay where they are currently located and the shape of the curve will change slightly.

The second mode for adding points is activated by clicking directly on a curve that does not have control points turned on - this will create a new point nearby the area you clicked, and existing points will shift slightly, but the shape of the curve will remain exactly the same as before.


Copies selected objects to the clipboard.

You can copy an edge of a solid to the clipboard, which will copy the curve of the edge. You can then use paste to create a copy of the edge as an independent curve object.

Copy with origin

Copies selected objects to the clipboard, with an additional step to define an origin point.

This is intended to be used in combination with the Paste part command which allows the pasted objects to be positioned and oriented to align to existing shapes. The origin point for the objects will be mapped to the target point picked during the paste.

This can be called either by right-clicking on the Copy button, or by the keyboard shortcut Ctrl+Shift+C.


Pastes in objects from the clipboard.

It is also possible to copy and paste objects between MoI and Rhino. Leave MoI running to enable this cross-application pasting.

Paste part

Pastes in objects from the clipboard, with an additional step for adjusting the orientation of the pasted objects, for example to align them to be perpendicular to an existing surface.

This is intended to be used in combination with the Copy with origin command which allows specifying an origin point for the copied objects, but it can also be used with the regular Copy as well. When regular Copy is used, the origin will be either the world origin or the cplane's origin if a custom construction plane has been set.

For more information on how the orientation works, see Orientation picker.

This can be called either by right-clicking on the Paste button, or by the keyboard shortcut Ctrl+Shift+V


Hides or shows objects.

If objects are selected when you press Hide, those objects will be hidden.

If no objects are selected when you press Hide, all hidden objects will be shown.

There is also an Isolate function available by right-clicking on the Hide button. Isolate will keep just the selected objects visible and hide all unselected objects. When you run Isolate a second time, everything will be restored to its pre-Isolate state.

If you only want to show some of the hidden objects instead of all of them, that is possible by holding down the Ctrl key when clicking the Hide button to perform a "show subset" operation. When doing "show subset", all the hidden objects will be temporarily displayed so that you can select which of them you wish to display. Once you have finished selecting, click Done or right-click and the regular display will be restored and any objects you did not select will return to being hidden.

In addition to this button, you can also use the Scene browser to hide and show objects in batches by clicking on the eye icons for different object categories. A left click on an eye in the scene browser will switch it between hidden and visible and a right click on an eye will isolate just that item and hide everything else.


Locks or unlocks objects.

When objects are locked, it prevents them from being selected but keeps them visible in the scene for either a visual or snapping reference. Snapping to locked objects can be enabled or disabled by a checkbox under Options / Snaps / Object snap options / Snap to locked objects.

By default when objects are locked, they switch to a grayed out color. It's possible to disable the color switch or adjust the color used under Options / View / Locked objects use alternate color. Uncheck the checkbox to avoid color switching, or click the swatch to adjust the color.

The Lock button works the same as the Hide button next to it.

Left click on Lock with objects selected to lock all selected objects.

Left click on Lock with nothing selected to unlock all objects.

Right click on Lock to "Isolate" the current selection by locking everything else other than the current selection. Right click again later on to restore back to the pre-isolate state.

Ctrl+Left click to do an "Unlock subset" which will temporarily show all current locked objects and allow you to select just a few of them to unlock. Once you have finished selecting, click Done or right-click and the regular display will be restored and any objects you did not select will return to being locked.

In addition to this button, you can also use the Scene browser to lock and unlock objects in batches. Hold down the Ctrl key when clicking on an eye in the scene browser to switch it back and forth between locked and unlocked.


Enables or disables history updating on an object.

Some commands have history updates enabled by default. For example, the Loft command will update the lofted surface if you edit one of the original curves. If you want to stop that updating, you can select the lofted surface, run the History command and click "Disable update". After that the lofted surface will no longer update when you edit the original input curves. Also, some commands have history disabled by default such as Transform / Copy or Transform / Rotate. You can use History / Enable update to turn history updates on for the results of these commands.


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