I read the Blender docs before I started this thread and I read it again now. I want to comment this doc a little bit because it does not really exactly explain how rotation in Blender works. Take it as a proposal to edit the doc.
Click and drag MMB on the viewport’s area: if you start in the middle of the window and move up and down or left and right, the view is rotated around the middle of the window. Alternatively, you can press and hold Alt while dragging LMB in the viewport’s area.
To change the viewing angle in discrete steps, use 8 NumPad and 2 NumPad (which correspond to vertical MMB dragging, from any viewpoint), or use 4 NumPad and 6 NumPad (or CtrlAltWheel ) to rotate the scene around the Z global axis, whatever being the point of view.
Concerning numpad 4 and 6 the doc is specific: The rotation is a rotation “around the Z global axis”. That means that this kind of rotation depends from the orientation of the global Z axis - and this orientation changes often as you work.
In particular this statement means: After numpad 7 was pressed the global Z axis points perpendicular in/out of the user screen. With this orientation of the Z axis the rotation is done in that way that the user always sees the same side of the object (clockwise or counterclockwise rotation). In almost all cases a user should not desire this. The user most often doesn’t want to turn a face, a body, a car or a landscape upside down. The user most often wants to walk around the object.
But after numpad 1 was pressed the global Z axis lays parallel to the vertical user screen edge. With this orientation the user can do what he/she most often wants to do: to walk around the object.
But the main problem is that the orientation of the global Z axis often changes and that the user must have a close look at the orientation of this axis in order to know what kind of rotation he/she will get with numpad 4 and 6 or with horizontal MMB. If the user does not watch the orientation of the global Z axis he/she will be surprised by unexpected rotations. This can a new user make crazy.
And what does the doc say about numpad 8 and 2 and about vertical MMB? Around what axis do these user actions rotate the object?
The doc doesn’t say anything about the corresponding axis. The reason is simple: A more precise description would reveal a fundamental inconsistency that most users will not suspect. Numpad 8 and 2 as well as vertical MMB do not rotate around any global axis but always around the view X axis (that lays parallel to the horizontal user screen edge). With this definition there is never a change in the way how vertical rotation will work. The global coordinates can have any orientation but vertical movement will always let the user walk around the object. This can a new user make happy.
This description considers only Turntable rotations. Trackball rotations I don’t consider here because this kind of rotation does move all global axis and no keyboard keys can perform it.
The doc should make the user aware that Numpad 8 and 2 and vertical MMB (or Orbit View Up and Down in the user preference settings) are bound to VIEW COORDINATES. Numpad 4 and 6 (or Orbit View Left and Right in the user preference settings) in the contrary are bound to GLOBAL COORDINATES.
Before I formulate a precise text for the Blender doc I still want to know if users can confirm the described behaviour. I already asked in my second and in forth posting if users can confirm the behaviour that I described. chip4brains wrote that 3 users have given suggestions for me. I understand this that this should show me that there is no configuration for a horizontal rotation that is independent from global coordinates. May be. But I still want a confirmation that rotation also on other installations works as I have described it here. For this confirmation I made a small CHECKING PROCEDURE:
- Activate turntable movement in user preference settings.
- Press numpad 7.
- Move with MMB horizontally or press numpad 4 and numpad 6.
On my machine the view rotates in that way that I always see the same side (rotation around the global Z axis or around the view Z axis). Both axis point after numpad 7 perpendicular in/out of the user screen.
This is NOT a desired behaviour.
Desired is: The view should rotate around the view Y axis so that I can walk around the object.
- Press numpad 1.
- Do absolutely the same as in 3)
On my machine the view now rotates in that way that I can walk around the object (rotation around the global Z axis or around the view Y axis) Both axis lay after numpad 1 parallel to the vertical user screen edge. Concerning the view coordinates the rotation axis is now the Y axis, not the Z axis.
This is a desired behaviour.
Please follow this procedure and let me know what you see.