Hello everyone!

This is the second of two basic-level tutorials on the main tools for selecting and transforming objects in their entirety (or: Object Mode) in Blender 3D 2.8; in this tutorial, in particular, we will see how to carry out the GRS transformations (Grab, Rotate and Scale) specifying numerical values, so we will talk about the pivot point of the transformations and the difference between global and local reference system when performing these operations.


GRS WITH NUMERICAL VALUES

In the previous tutorial we saw how to select and move one or more objects in the scene in a free way, by pressing GRS for translations, rotations and resizing, possibly clicking on the axes of the various transformation manipulators, which we can recall by opening the Tool Shelf panel (shortcut T) , on the left in the 3D Viewport; we have also seen how to set the units of measurement of the Blender scene, for example, to identify lengths and distances in cm or in meters.

 

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Setting precise values for movements, rotations or resizing is very simple: just type the shortcut of the operation to be performed (G, R or S), followed by the extent of the transformation, then Enter; for example:

  • to move the selection along the X axis of 2 units (be they meters, cm or other: it depends on what you have set in the Scene - Units tab, in the Properties editor), type G, X, 2 and press Enter;
  • to rotate the selection 30 degrees around the vertical axis of the scene, ie the Z axis, type R, Z, 30 and press Enter; this applies, of course, if the Rotation field of the Scene - Units tab is set to Degrees;
  • to uniformly resize the selection, type S and a scale factor; for example, to halve the size of an object, type S, 0.5 and Enter, because obviously 0.5 is equivalent to "a medium"; to triple its size, instead, type S, 3 and Enter;
  • in the previous tutorial we have seen that it is possible to carry out a resizing even on a single axis, using the scaling transformation manipulator; it is possible to carry out such an operation also by typing the commands, simply by specifying the axis of the operation immediately after S, as happens with the movements and rotations; for example, to double the size of an object along the X axis, type S X 2 and Enter.

Note that I talked about selection, not object, because these operations are valid also on multiple selections of objects, not on one object at a time; for example, using one of the selection tools seen in the tutorials published previously on this website, we select all the objects present in the 3D scene, then type R, Z, 45 and press Enter, to rotate the whole selection around a point ...

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… ok, but what is this point? Can we set a different point for transformations, especially when it comes to rotations, both for individual objects and for multiple selections? The time has come to talk about the Pivot-Point or pivot point of the transformations.


THE PIVOT-POINT OF THE TRANSFORMATIONS

By default, the transformations are carried out with respect to the midpoint of the selection, considering as the center of each object a specific point, called the "Origin" of the object.

Usually, a newly created geometric object has the Origin at its center, as happens for example with the cube present by default; the virtual camera, on the other hand, has its Origin on the bottom, because by rotating it you can simulate the transformations that take place in the real world, when you direct the lens of a camera towards a point in the scene.

By selecting both the camera and the cube, therefore, Blender will calculate the midpoint of the selection and, as a rule, perform the transformations around that point.

The settings relating to the Pivot-Point (pivot of the transformations), are found in the "Pivot-Point" selector, in fact, at the top center in the 3D Viewport; these are a few items and all very important, so I will pass them all over.

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The item that is selected by default is Median Point and its modes are now clear: Blender averages the Origins of the various objects selected and performs the transformations around that point.

"Individual Origins" operates intuitively, making the transformations for each object of the selection in reference to its own Origin..

When we make a multiple selection, as in our case, the last selected object is called "Active Object" and its name is shown at the bottom right of the program window; the "Active Element" mode allows us, as the name suggests, to use the Origin of the active object as the pivot point of the transformation.

Bounding Box Center identifies a virtual "box" that incorporates all the objects of the current selection and performs the transformations in reference to the center of this box.

The fifth mode is 3D Cursor, which from the name makes us understand that the transformations will take place, precisely, with respect to another object, called "3D Cursor". It is a purely virtual object (in the sense that it is not provided with a geometry and is not rendered in the final image, if framed by the camera); you can locate it, in the 3D scene, because it is represented with a characteristic icon, similar to a viewfinder.

To position the 3D Cursor in a point of the scene, in a free way, select "Cursor" among the icons of the Tool Shelf, in the 3D View, then click in any point in the 3D view.

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To position the 3D Cursor in a precise point of the scene, knowing its coordinates, open the Transform panel on the right in the 3D Viewport (shortcut N), then open the View tab and set the position and eventually rotation of the 3D Cursor in the 3D Cursor section.

Let's see for example how to rotate the objects of a multiple selection around the Origin of the virtual scene using the 3D Cursor as Pivot-Point.

We set 3D Cursor as a pivot point in the top-center menu in the 3D scene, then change the 3D Cursor coordinates to 0,0,0, for Location X, Y, Z, in the View - 3D Cursor tab of the panel, so to place it at the center of the virtual universe.

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At this point we will be able to carry out our operation: the Origin of the single objects will be transformed in reference to that point; for example, with R Z 30 we will have a rotation around that point, while with Scaling we will approach or move objects away from the 3D Cursor and resize them, in the meantime.

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SETTING EXPLICIT VALUES FOR POSITION, ROTATION AND DIMENSIONS

The operations we have seen so far concern transformations, but how can we explicitly set the coordinates in space, or an angle of rotation or, again, the size of an object?

We basically have two possibilities: type in coordinates, orientations and dimensions (or scale factors, with respect to the original size of the object) in the Item - Transform tab of the 3D Viewport, or type the same information in the Object tab of the Properties editor.

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For example, place the cube back in the center of the scene, with rotation 0 and its original size (ie, returning its scale factor to 1.0): type 0 in all the Location XYZ and Rotation XYZ fields in one of the two tabs, while in the Scale section, type 1 for the three XYZ fields.

The Dimension values (the size of the object) will change automatically; obviously you can also set explicit dimensions for the object; here, since I wanted to bring it back to its original size, I modified the Scale values, taking them all to 1.

Note that, in the case of multiple selection, the values entered in these tabs will refer to the active object.

It must be said that it is possible to change the settings of a transformation even immediately after making it, using the operator menu visible in the lower left corner of the 3D Viewport; for example, after having doubled the size of the selected object with S, 2 and Enter, we will be able to open the panel at the bottom left, now called "Resize" (from the name of the last operation) and change its values, for example by typing 3 for Scale X.

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This panel will be available to edit, after making them, [almost] all the operations available in Blender, so start keeping it in mind.


GLOBAL AND LOCAL REFERENCE SYSTEM

As the last topic of this tutorial, I introduce one that will be included in many others, when things will become more interesting: the distinction between global and local reference system, while performing operations.

So far we have carried out all the operations with respect to the global reference system, ie that of the virtual universe of Blender, but this method has strong limitations when we want to make nontrivial transformations.

For example: after resizing the cube on X and rotating it 30 degrees around its vertical axis, for some reason we want to translate it along the longer faces, which originally - without rotation - we would have identified as those perpendicular to the Y axis , but now a global Y translation would not have the desired effect ...

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The cube - and, incidentally, every scene object - also has its own reference system, called LOCAL, which at the beginning coincides with the global one of the scene, but which is independent of it and which is particularly useful after some transformations , like rotations.

To view the Local reference system of an object, select Local from the Transform Orientation menu at the top center in the 3D Viewport.

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The arrows of the translation manipulator will change orientation, reproducing those of the Local system of the cube, so now we can click and drag on the arrow of the Y, which this time will be LOCAL, as desired.

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As for the shortcuts to be used for the various transformations, it changes very little: we will have to type the letter of the axis twice, immediately after the operation shortcut; for example:

  • to rotate it 30 degrees around the global Y axis, we will type R, Y, 30 and Enter; then to rotate it 45 degrees around the local Y axis, we will type R, Y, Y, 45 and Enter;
  • to move the object by 3 units along the global X axis, we will type G, X, 3 and Enter, while to move it by 3 units along the local X axis we will type G, X, X, 3 and Enter.

Well, that's all for this tutorial!

See you soon!