Use modeling aids
Cursor constraints and modeling aids assist in accurately locating objects in 3-D space.
The cursor can always move freely in space, but you will normally want to relate your modeling elements to the construction plane grid, existing objects, or coordinates in space.
Cursor constraints
There are two parts of the cursor: the cursor (1) and the marker (2). The cursor always follow the mouse movement.
The marker sometimes leaves the center of the cursor because of some constraint on it such as grid snap or ortho. The marker is a dynamic preview of the point that will be picked when the left mouse button is clicked.
When the marker is constrained, in elevator mode, for example, a tracking line (3) also displays.
Constraints move your marker to a specific point in space or make its movement track according to the constraint so you can model accurately.
Angle cursor constraint
Restrict the angle the cursor can travel.
Point filters
Extract individual x, y, and z coordinate values to create a new, composite coordinate.
Restrict cursor movement to an angle.
Limit picking locations to an elevation.
Toggle the current snap mode state.
Modeling aids
Set the construction plane in the active viewport.
Specify the plane object dragging will be parallel to.
Move objects a small increment using arrow keys.
Constrain the marker to an exact location on an object such as the center of a circle or the midpoint of a line.
Turn on a system of temporary reference lines and points.
See also
Measure objects
Rhino for Mac © 2010-2017 Robert McNeel & Associates. 24-Oct-2017
Ortho
Planar
CPlane
DragMode
Nudge
Object snaps
SmartTrack