Fix Constrained Orbit

[maruska]

As along time Alias user, I prefer Constrained Orbit as my navigation model. I like to "tumble" a product as if it were an object on a table rather than as if it were free floating in space. I find this grounds it better and allows me to evaluate it as a real thing.

I find all too often, Fusion's Constrained Orbit navigation gets all catawampus and starts acting like a free orbit mode. The Y-axis should stay vertically aligned at all times.

J.

[roambotics_scott]

I've run into the same and very strongly suspect what's happening there is gimbal lock ( https://en.wikipedia.org/wiki/Gimbal_lock ; actually I don't recall but think someone might have even submitted an idea for that before http://forums.autodesk.com/t5/fusion-360-ideastation-request-a/gimbal-lock/idi-p/5194977 )

If that's the case, they're just using a poor choice of representation of angles (like roll-pitch-yaw) and you're running into a mathematical singularity where that coordinate system breaks down.

Also if that's the case, it's trivial to fix by internally switching to a better representation of angles (*cough* quaternions *cough*)

[mstrater]

I think you might be getting confused by the fact that constrained orbit chooses which is the constrained up vector depending on the orientation of the model when starting the constrained orbit.

Try this:

Open a model, press the home icon of the view cube, and start rotating in constrained orbit mode. Notice that lateral mouse movement causes the model to rotate about the axis that goes between the Top and Bottom faces of the view cube.

Press the home icon on the viewcube, then press the Front face of the view cube, and then the rotate right arrow.

Your view cube should look like this now:

Now try using the constrained orbit again. Notice that now lateral mouse movement causes the model to rotate about the axis that goes between the Left and Right faces of the viewcube. This is because when you started the constrained orbit, this axis was pointing upward, so it was chosen as the constrained up vector.

I'm guessing that you are looking for an option to make the constrained axis remain constant between the Top/Bottom axis then?

As far as I know that doesn't exist today, but if you want constrained orbit to always constrain rotation around the Top/Bottom axis, make sure that axis is pointing up when you start the constrained orbit.

-Max

[maruska]

I'm not sure what I'm doing wrong then. I don't regularly use the view cube, so I would think that if I'm not deliberately changing my orbit axis, then Y should always be up, but I often find my model is rotating around an arbitrary axis.

So I guess I'll rephrase my idea request: I would like a constrained orbit that acts like Alias.

[maruska]

@roambotics_scott Oh and yes, I thought about the gimbal lock issue as I've done quite a bit of work with quaternions, but oddly, the behavior I'm looking for is a way simplier navigation model to code for as it intentionally has a pole position at the top and bottom if the up vector. 

[roambotics_scott]

Yeah @maruska I realized I was barking up the wrong tree 🙂

[maruska]

No worries. Bringing up the gimbal lock and quaternion math is important to understanding the interaction. 

[promm]

Thank you for your idea - this is getting archived due to lack of votes.

Cheers,

Mike Prom