Object snaps

The object snaps constrain the marker to an exact location on an object such as the end of a line or the center of a circle.

• When Rhino asks you to choose a point, you can constrain the marker to specific parts of existing objects by turning on object snap modes.

• When an object snap is active, moving the cursor near a specified point on an object causes the marker to jump to that point.

• Object snaps can persist from pick to pick, or can be activated for one pick only.

• Multiple persistent object snaps can be set in the Osnap control.

• All object snaps behave similarly, but snap to different parts of existing geometry.

• For example, the End object snap finds the endpoint of a curve. When activated, the end object snap constrains the marker to the endpoint of the curve closest the cursor.

Multiple object snaps

More than one object snap can be active at the same time. As the cursor passes over an object, the appropriate object snap displays.

Persistent object snaps

Use persistent objects snaps to maintain an object snap through choosing several points without having to reactivate the object snap. Only Cen, End, Int, Knot, Mid, Near, Perp, Point, Quad, Tan, and Vertex object snaps can persist.

You can set the Snap radius for object snaps. This means how close you have to move the cursor to the point before the marker jumps to the point.

One-shot object snaps

One-shot object snaps only work when Rhino is requesting a point, are turned on for one pick only, and override all persistent object snaps for that pick.

Object snaps when dragging

When object snaps are on, click and hold near object snap locations to use them for the start or end locations of the drag.

To suspend object snaps for the drag, press and hold Alt.

Project object snaps

The Project button on the Osnap control projects any object snap to the current construction plane. For example, in the illustration, the curve projects to the construction plane from snapped locations on an object.

See: ProjectOsnap

Object snap culling

Object snaps work on visible objects only by default. Objects that are obscured by other objects cannot be snapped.

When the cursor passes behind the red box, the object snap turns off.

Simple object snaps

Simple object snaps snap to one location on an object.

NoSnap

If a command is active, NoSnap turns off persistent object snaps for one pick.

Center (Cen)

Snaps to center of:

1. Closed planar polyline. (Average coordinates of corners)

   

2. Circle, ellipse, or arc. (Exact or approximate)

   

3. Single surface with a boundary of (1) or (2). (No holes)

   

4. Annotation text bounding box.

   

See: Modeling Aids Options.

End

Snap to the end of a curve, text corners, interior vertices of polylines and joined curves, the seam point on closed curves, and the "corners" of surfaces, and polysurfaces.

Intersection (Int)

To isoparametric curves, use the OnSurface or OnPOlySurface object snap first.

To snap to mesh wires, the SnapToMeshes command has to be enabled.

Knot

Snap to a knot on a curve or surface.

Midpoint (Mid)

If you place four smart points, A, B, C and D, only the midpoints between A and B, B and C, or C and D can be snapped.

To snap to mesh wires, the SnapToMeshes command has to be enabled.

Near

Snap onto a curve, mesh wire, or surface edge at the cursor location.

To snap to mesh wires, the SnapToMeshes command has to be enabled.

Perpendicular (Perp)

The Perpendicular object snap is not effective for the first point of a command.

To snap to mesh wires, the SnapToMeshes command has to be enabled.

Point

Snap to a point object, extrusion point, control point, edit point, block, and text insertion points.

Also snaps to centers and corners of rectangular lights and block insertion points even if control points are not displayed.

Quadrant (Quad)

Snap to the point on a curve that is at the maximum x or y point relative to the current construction plane.

Note

• The quadrant points of circles and arcs are at the extremes in each construction plane axis direction.
• Ellipses have quadrant points at the ends of the ellipse axes if the ellipse is oblique in addition to those at the construction plane extremes.
  

Tangent (Tan)

Snap tangent to a curve.

The Tan object snap is not effective for the first point for a command.

Wikipedia: Tangent

Vertex

Snap to a mesh vertex.

Note

• Use the CullControlPolygon to disable snapping to vertices on the back side of mesh objects.
• Mesh vertices do not have to be turned on when using the Vertex snap.

Object snaps using references

When picking points during these steps, use simple snaps (End, Near, Point, Midpoint, Center, Intersection, and Quadrant) for greater precision.

Along

Track along a line.

Along example

Start a circle located on the line between the center of the circle and the end of a line.

AlongParallel (AlongP)

Track along a line parallel to a reference line between two points.

AlongParallel example

Start a line along a line parallel to the rectangle that passes through the circle's center.

Between

Snap midway between two specified locations.

Between example

Center a circle between two rectangles

From

Snap from a specified base point.

Note

• The From object snap differs from the rest of the object snap because it is used to set the base point for ortho, distance constraint, angle constraint, and relative coordinate entry.
• Ortho constrains the marker to lines radiating from the last pick point. Similarly, distance constraint constrains the marker to a circle of a specified radius from the last pick point. You can set this point, without picking it, with the From object snap.

From example

Center a circle four units from the endpoint of a line.

PerpendicularFrom (PerpFrom)

Track along a line perpendicular to a curve or surface.

PerpendicularFrom example

Draw a line perpendicular from a line at the intersection with the circle.

TangentFrom (TanFrom)

Track along a line tangent to a curve.

Wikipedia: Tangent

TangentFrom example

Draw a line tangent from the circle at the intersection with the line.

Object snaps on an object

OnCurve (OnCrv)

Snap to and track along a selected curve for one pick.

Notes

• The OnCrv object snap is useful if the model is complex and Near object snap alone does not lock to the object you would like it to.
• The curve parameter displays in the status bar when moving the mouse along the curve.

OnCurve example

Select the curve to move a control point along.

PersistentOnCurve (POnCrv)

Snap to and track along a selected curve until the command completes.

OnPolysurface (OnPSrf)

Snap to and track over a polysurface for one pick.

OnPolysurface example

Place a point object on a polysurface.

PersistentOnPolysurface (POnPSrf)

Snap to and track over a polysurface until the command completes.

OnMesh

Snap to and track along a selected mesh object for one pick.

PersistentOnMesh (POnMesh)

Snap to and track along a selected mesh until the command completes.

OnSurface (OnSrf)

Snap to and track over a surface for one pick.

OnSurface example

Place a point object on a surface.

PersistentOnSurface (POnSrf)

Snap to and track over a surface until the command completes.

Percentage (Percent)

The selected curve is marked with temporary black points that can be snapped when the Point object snap is disabled.

If the percentage is less than 50, the curve is marked with multiple snap points. For example, when using 30, you get snap points at 30%, 60% and 90%.

Isoparametric curve snapping

You can snap to surface isoparametric curves using the Int object snap whenever the input is constrained to a surface, for example in ExtractIsocurve, InsertKnot, OrientOnSrf, and with OnSrf, and OnPolysrf one-shot object snaps.

isoparametric curves object snapping is "weaker" than normal object snaps. The normal object snaps are evaluated first, and only if they fail will Rhino try to snap to the isoparametric curve intersections.

Scripting one-shot object snaps

One-shot object snaps are automatically transparent. In other words, when scripting these, you do not need to use the apostrophe character to make the object snap work while a command is running.

The Osnap command sets the status of object snaps from the command line.

Note

• This command is useful for scripting, because it can set any object snap combination from command line.
• You can temporarily suspend the effect of the object snaps with the DisableOsnap command.

The ShowOsnap command turns the floating Osnap control on, off, or toggles the current state.

The DisableOsnap command manages the state of persistent object snaps.

The ProjectOsnap command projects object snaps from the actual snap point to the construction plane.

The SnapToLocked command snaps work on locked objects and on objects on locked layers.

The SnapToOccluded command allows object snaps to work on objects that are hidden behind other objects.

See also

Model with precision

Cursor constraints