Units in "Set Export Scale"

When doing camera tracking and in the export operation choosing to set the scale from selection a dialog opens asking you to "Enter the real world distance between the two points xx and xx". However, I can find no reference as to the units that should be used for this input.

When I select tracking points that should be (say) 1 metre apart, I get suggestions of 0.0058 "units" in the dialog box so unless the unit is supposed to be kilometers, this isn't even close.

Can't find any help on this in the fusion 9 manual so perhaps someone can help.

I asked this question over a year ago and still nobody has answered. Is it that nobody knows?

I don't think it actually matters except for you as an end user. As long as the field of view of the camera matches then your solves will match - optically - this is how they created on-set matte paintings and hanging miniatures and that's how they managed to capture Frodo and Gandalf in a single shot.

So just set it to a value that you can remember as being 'real world' - if it's 10 cm, set it either a 10 or 0.1 or 4 (to convert it to inches). As long as you remember to build the rest of your 3D world to the same scale you should be good to go.

By and large Fusion's 3d system is unitless. It doesn't have any dynamics systems, so real-world scale isn't really an issue. Thus, you can decide a Fusion unit represents whatever you like.

Thanks for the replies.

It's interesting that obviously the 3D objects I'm importing into some of my scenes vary wildly in their own size paramaters because sometimes I have to use quite a large number for the "export scale" in order that the "size" on the FBX node doesn't have to be set to some ridiculously small number like 0.001 -- yet on other occasions I have to set the "export scale" to fairly small numbers of the 3D object is way too small to even be seen.

That's the problem when using freebies (.obj files) off the Net I suppose

Since you're using freebies of the net anyway, why not run those through freebie Blender to scale them to what you need so you won't have to mess as much with the settings inside of Fusion?