How does one use the "Alt" key in combination with the Right Mouse Button?

StephenG

I think I have pretty much mastered all the various "Onshape Default" methods to view 3D models and 2d drawings, however, I am baffled by using the "Alt" key in combination with RBM. 

Here is what Onshape Online Help says....

  Windows Mouse:

3D Rotate: Right-mouse-button-click+drag   Zoom in and out: Scroll up and scroll down, respectively   2D pan: CTRL-right-mouse-button+drag (middle button click+drag)   Press the Alt key to animate to nearest 'floor down' view (the nearest view without any roll)   Holding Alt+Right Mouse results in horizontal mouse movement around the model, and vertical mouse movement pitches over the model

The Alt key does something sometimes, but I cannot make any sense of the behavior relative to predicting/controlling what it does. 

I would appreciate if someone could explain how the Alt+RMB works.

(I know it might be a lot to ask, but it would be very helpful if someone could generate a video of the ALT+RBM in action.) 

MBartlett21

@StephenG

It makes the z-axis stay vertical. Try moving your mouse in circles while rotating with and without the alt key being held down

Gib_Jeffries

This is a nice feature. It helps with design reviews where you want to keep the view oriented vertical-up.

StephenG

Sometimes I see that effect: "makes [Global] Z-Axis stay vertical". Actually, what I observe is the Z-Axis snapping vertical and sometimes normal to the screen and then the RMB view rotation appears to exhibit its non Alt behavior. Again, I only see this behavior sometimes, it is unpredictable.

I would have thought that depressing and holding down the Alt key with RMB movement, after snapping it vertical/normal, would maintain the global Z-Axis in a fixed screen orientation.

On-Line Help says...

"Holding Alt+Right Mouse results in horizontal mouse movement around the model, and vertical mouse movement pitches over the model."

The above description makes sense with respect to having the viewing (camera roll) constrained either perfectly horizontal, or perfectly vertical with respect to the screen (the observer) based on the movement of the mouse; ex. movement that is more screen horizontal than vertical would produce a view angle rotation about the vertical screen axis. But this is not what I am experiencing.

Jake_Rosenfeld

@StephenG

Does what you're seeing look different than what's presented in the "Z-Axis Rotation" video on this page:
https://www.onshape.com/cad-blog/whats-new-in-onshapes-latest-update-09/15/2016

Neil has a good way of explaining it when he says "The Z axis will remain vertical with respect to the screen." (a.k.a. holding down alt should make sure that the blue line on the view cube is always straight up and down).

One way to imagine what this type of rotation is trying to accomplish is if you imagine your design sitting on a table, and you can walk around the table and look at the design from above or below, but you can't tilt your head side to side.  You can still change whether your head is level with the table, under the table looking up, or over the table looking down, and walk all around the table.

StephenG

The referenced video from the 9/2016 update shows exactly the behavior I am experiencing. (Thanks for the background as to why this capability was added: to get the model in a more natural/acceptable (table top) orientation for viewing.) 

However, once the z-axis vertical is established it is not locked while the Alt key is depressed; if you look closely at the video the Z-axis wanders away from perfect vertical. The Z-axis does not remain locked in a vertical orientation. However, the camera view roll around the screen horizontal is much less sensitive to vertical mouse movement which really helps support the walk around the table effect keeping the Z-axis predominately in a vertical orientation.   

I noticed the the Z-axis can snap vertical either up or down depending which is the shorted rotation path to make it vertical. It also appears the Z-axis must be "close" to vertical for it to snap to vertical otherwise the Alt key has no effect. I swear I have had the Z-axis snap normal to screen. 

Now that I have a better understanding of its intended purpose I will definitely use it more.

jrs_spedley

Rather than start a new topic for such a linked post I'll just add a bit here.

2D pan: CTRL-right-mouse-button+drag (middle button click+drag)

For me panning with the middle mouse button often causes the window contents to re-centre and resize to fit all.  Using CTRL-right-mouse-button+drag doesn't do this.  I'm sure it irritates at least one other person here!