Well, the more or less obvious choice is to use what has always been used: cursor keys. However, they move on a bidimensional plane, and if you have a 3D software, then you obviously need the Z-axis. For this, I'd suggest a combination of keys that you don't currently use as a shortcut, or maybe use the UP arrow (since it's a view from above) combined with a close key. And then we have another problem. See this QWERTY keyboard for Mac:
Now take a look at this QWERTY keyboard for Mac (it's mine, a bit used as you can see):
And now yet another QWERTY keyboard, this time for PC:
(And I could continue with many more examples.)
As you can see, there are no keys that are close and in the same position throughout all keyboard layouts. And we're talking about just QWERTY, let alone other physical configurations and language-based configurations!
So, I think the best you could do is to use CTRL+UpArrow as long as you don't use that combination already.
The assistive technology version
Another option to consider, if it's within your possibilities, is to use voice-activated commands. If not for everything, at least for these commands. Your application will become accessible, and you will provide an easy solution to all users, even those without accessibility concerns.