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Puzzled by rotations (by Maurizio Ferreira)
I really don't understand how rotation of a linked object works.
Just to do some experiment, I've made a simple cube object and than imported it in a new project.

I'm able to select , move and rotate it, but it seems to me that the 'pivot' point of rotation is arbitrarily selected.

Some time, selecting and edge of the cube and trying to rotate, it rotates around the near corner, other times it rotates around a different corner, and other times it doesn't rotate at all.

Using the Ctrl button a green line appears, with an extremity fixed on a point of the screen and the other that follows the mouse movement.

To show it I have to click on an edge, drag the object somewere, press the ctrl button and drag around the mouse.
The origin of this line seems to be the location of the first click.
However if I move the mouse near this original point, the rotation stops.

If I click on an edge, and press the ctrl button without having dragged the object, the rotation does not starts.

Any explanation ?

Best regards.

Maurizio.
Sun Sep 8 2019, 06:32:57
Partial answer (by DIV)
Hi, Maurizio.

Actually with your question you have solved a problem I had, so thank-you very much!
I had a cylinder inserted in an annulus, each with various features. Each has 1 DOF (rotation around axis). The file is assembled from two separate "part" files. I can rotate the cylinder just by dragging. I couldn't rotate the annulus at all until I read your note about holding down the Ctrl key.

OK, so here is what I noticed, in my assembly.

Dragging with mouse only:
* Can rotate cylinder; cannot rotate annulus.
* Need to sort of push/drag the selected point around screen with the mouse.

Dragging with mouse + Ctrl:
* Can rotate cylinder & annulus.
* Do NOT need to push/drag point around screen with the mouse.
* Initial mouse-click defines a (temporary) reference point, and you need to move the mouse around that reference point. Depending upon the position of your mouse with regard to that reference point, the point on the sketch/object will rotate accordingly. The green (construction) line that temporarily appears is just to help visualise the rotation that you are requesting.
* The length of the green line (i.e. the distance of the mouse from the temporary reference point) is irrelevant. Therefore it may be convenient to manipulate a part that moves around the entire sketch window while just making small movements with the mouse around the temporary reference point.
This all seems consistent with the behaviour that you described when pressing the Ctrl key.

Dragging with mouse + Shift:
* Can rotate cylinder & annulus.
* Do NOT need to push/drag point around screen with the mouse.
* Actually, the part sometimes rotates in the same direction as the mouse movement, but sometimes it rotates in the opposite direction to the mouse movement.

I am comfortable with my understanding of the effect of Ctrl.
As yet I am not too sure of the difference between no-key and Shift: my best guess is that pressing Shift instructs SolveSpace to use a different reference point: e.g. rotate by comparing mouse to one of the "origins" defined on the sketch (could be for the part selected, could be the global origin).

Hope this helps you a little,
DIV
Sat Oct 12 2019, 03:31:14
Shift versus Control (by DIV)
Suppose we treat the viewing plane at the origin as the 'equator'.

Then the Control key provides rotation of varying azimuthal angle (with constant polar angle).

Whereas the Shift key allows changing of the polar angle (with constant azimuthal angle.

https://en.wikipedia.org/wiki/Azimuth#Polar_coordinate
https://en.wikipedia.org/wiki/Spherical_coordinate_system
Sat Oct 12 2019, 04:51:39
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