The 3D Cursor

Today’s Blender Tutorial is brought to you by Roger Waggener!

Blender’s 3D cursor is the red and white ring that shows up in the middle of a new, empty Blender file. [fig1]

fig1

It’s primary use is to specify the location in the scene at which new objects are added. However, when coupled with Snapping modes and Transform/Scaling modes it has other very useful functionality.

As I mentioned, all new objects added to the scene appear at the location of the 3D cursor. If you want to add an object at a location other than the center of the scene, left click at the desired location to reposition the 3D cursor then add the new object. When you left click, the 3D cursor is always placed in a plane parallell to the viewport, so it’s easiest to precisely locate the 3D cursor by placing it when in a cardinal view (top, side, front) and then refining it’s location in another cardinal view. For instance, hit the num-7 key to go to the top view, left-click in the desired X-Y location, [fig2] then hit the num-3 key to go to side view and set the Y-Z location. [fig3] [fig4]

fig2

fig3

fig4

The 3D cursor can also be used as the pivot point for manipulating objects and object elements (vertices, edges, and faces).  The pivot point is the point about which manipulations take place. For instance, the center about which a rotation occurs. Blender’s default pivot mode is Median. In Median pivot mode, when you manipulate an object or group of objects or an object element or group of elements, the pivot point will be at the centroid of everything that’s selected. [fig6][fig7]

fig6

fig7

Sometimes it is very useful to be able to reset the pivot location for manipulation. This is done by changing pivot mode to 3D Cursor. The easiest way to do that is to type the period ‘.’ key (not the decimal key on the number pad- that centers the viewport on what is selected). It can also be set in the Rotation/Scaling pivot selector which is just to the right of the Viewport Shading selector on the header of the 3D viewport window. [fig5] In 3D cursor pivot mode, the 3d transform manipulator appears at the 3D cursor whenever something is selected. Furthermore, when the tranform manipulator is used, any transforms applied will be centered at the 3D cursor.

fig5

In object mode, the entire object is translated, rotated, or scaled about the 3D cursor instead of the object center. In edit mode, whatever elements are selected are translated, rotated, or scaled about the 3D cursor. This can be very useful in many cases. [fig8][fig9]

fig8

fig9

Example:

fig10

For instance to create the object in Figure 10, [fig10] follow these steps- add a cube, enter edit mode, hit the period key ‘.’ to enter 3D cursor pivot mode, select the bottom edge of the left face [fig11]  and snap the 3D cursor to that edge by hitting shift-s and selecting ‘Cursor to Selection’. [fig12] The 3D cursor will snap to the center of the edge. [fig13]

fig11

fig12

fig13

Now you can extrude the left face and rotate it about the bottom edge by entering face mode, [fig14] hitting ‘e’ for extrude, hitting return to prevent moving the face,  and then using the transform manipulator to rotate the extruded face. [fig15] You can hold down the control key to constrain the rotation to 5 degree increments. Continue extruding and rotating until your shape is complete. [fig16] One thing to keep in mind is that there are now multiple sets of vertices at the end points of the edge you rotated around. You can get rid of them with the ‘Remove Doubles’ button in the editing window. Hit the ‘a’ key to select all (you may have to hit it twice to select everything) since Remove Doubles only affects what is selected, then click the Remove Doubles button. [fig17]

fig14

fig15

fig16

fig17

Now you should have some new ideas about what you can do with the humble 3D cursor- especially when coupled with 3D cursor Pivot Mode. Of course, the best way to learn Blender is to experiment based on your existing knowledge so try to come up with some new tricks and techniques to use with the 3D cursor. If you arrive at something useful, please share it in a comment.

In my next Thingiverse blog post I’ll talk about object centers.