The example code passes 0.03 to setRadiusSearch, with a comment "Use all neighbors in a sphere of radius 3cm." That confuses me as I've been assuming that setRadiusSearch would take an Euclidean distance value as measured in the particular cloud's coordinate system, rather than any actual Metrics value. Am I missing something in PCL where this transformation is done intelligently?
I can't be sure, because I'm also new to PCL, but from what I've seen, you're correct.
When specific units are referenced it's not because those units have been ascertained from the data, but rather it's generally known that (for example) Kinect data is in meters. So, 0.03m is not a proper conversion, but happens to be known by the writer of the tutorial.
...also, your message hasn't been sent to the mailing list. You have to sign up, for that to happen (that's why it says something about your message having "not been accepted" at the top). It shows up here, but doesn't get sent to the mailing list.