Mouse Navigation Question

[designcomputer]

The below seems to be a problem with the orientation of the model that can't be fixed using the UI. Any help would be appreciated.

I've successfully gotten instant-ngp up and running on my Windows 10 PC with an RTX 2080Ti but I am having problems navigating with the mouse in my first project. It must be easy because all of the videos show people doing it naturally and it isn't even mentioned in any of the documentation I've found. I can move the object by holding the mouse wheel and dragging it. I can zoom in and out with the mouse wheel. I can rotate the object up and down at a point somewhere between the y and z axis by left clicking and dragging up and down. But for the life of me, I can't figure out how to rotate around the red x-axis as shown in the image below. The shift and alt key used in combination with the left mouse button or wheel button has no effect. Is there a way to set the center of rotation and the axis you want to rotate on?
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I've run the Fox demo now and the mouse navigation works for me on that. So maybe it has something to do with the orientation of the axis or the way my source images were interpreted.