Ingmar Franz (duerer)

8 replies · posted

Strange Behaviour of Moving Objects with "3D Cursor" as "Pivot Point"

I've encountered a problem with the movement of objects if the pivot point is set to "3D Cursor": You can recreate it with Blender's default scene: 

1) Take the default cube and set the pivot point to "3D Cursor". Now place the mouse pointer over the origin of the default cube and move it with pressing "G": The object origin will stay under the mouse pointer during the movement. 

2) Repeat the test with the 3D cursor placed far away from the cube: Same result. 

3) Now place the cube and the 3D cursor again at the world origin and add a second cube which you scale to 0.1 along "Global Z" and 1000 along "Global X" and "Global Y". Place the 3D cursor on that ground plane far away from the default cube. Place the mouse pointer again over the origin of the default cube and move it with pressing "G": The object moves away from the mouse pointer when moving the object towards the screen edges. 

4) Repeat the same test with "Active Element" as pivot point and the cube's origin will stay under the cursor. 

How can this be explained?

  • duerer I can't explain this, but I think it has to do with perspective. try your tests in Orthographic View.

    I do not know why the perspective is affected by the Pivot Point, but I can imagine that it would be...

  • Somehow, when you set the Pivot Point to the 3D Cursor, the Mouse Pointer appears to be 'connected' to the 3D Cursor. (When you try to Scale, there is a 'line' between the two...)

    Imagine a Plane, parallel to your screen and going through the 3D Cursor. This is the plane that your Mouse Pointer moves along.

    If you have your 3D Cursor 'in front' of the Default Cube, then your Mouse appears to move faster than the Cube (or any Object) and if the 3D Cursor is 'behind' the Cube, then the Cube appears to move faster. (Parallax effect..)

    •  Thanks, spikeyxxx,this sounds plausible 😀👍! It just astonishes me that the "Pivot Point" at least in this case also affects translations and not just scalings and rotations. 

    • Just a short addendum: The Blender 2.93 Manual here just writes:

      "All rotation and scaling transformations will now be done relative to the location of the 3D cursor. "

    • duerer and that is correct!

      Translations are completely independent of the position of the 3D Cursor (or any other Pivot Point).

      The (visual) difference, when translating, is only due to the 2D plane, the Mouse is moving through, whose (the 2D plane's) position depends on the Pivot Point...

      Man, this is sooo hard to explain in words ;)

    • spikeyxxx Let me explain it in other words 😉: The "3D Cursor" as  "Pivot Point" doesn't influence the movement of the object itself but where the calculated position of the mouse pointer is. This results in different visual speeds of the translated object and the mouse pointer's if the "3D Cursor" and the translated object are far apart from each other. So you get the strange feeling of not really controlling your object because you normally use  the mouse as the visual controller of the moved object .

       Switching to "Orthographic View" reveals that the absolute movement of the mouse pointer on its plane is the same for a certain distance that your mouse has been moved on its pad since mouse pointer and object are now moving with the same visual speed due to the lack of "Perspective Distortion".

      PS: Was this short enough 😉?

    • Excellent duerer

    • spikeyxxx I have a good teacher with you 😀👍!