Hi isaac, I've been experimenting some with SketchUp, I can't really seem to follow the same steps that I showed above. I can draw the first vertical rectangle (note that it is at an arbitrary angle and not aligned to the base x/y plane), but I can't seem to activate an inference that tracks perpendicular away from an existing vertex to start drawing the second rectangle... (I can get it if a draw an actual line going perpendicular, but not just trying to track away from it to start the next drawing away from it).

I think that is generally a problem with that kind of "automatic" hovering based inferencing, it can need to be rather conservative about how many things it snaps on to because it is just too easy to automatically fill the screen with inferenced snap lines.

The nice thing about MoI's method to do this, is that I know for sure when you want to activate the "inference", so I don't have to hold anything back at that point, I can give all the same snaps that you would have for drawing a real line at that time, instead of only just some subset of them...

I don't think that there is anything you can do with inferences that you can't do with construction lines, if you're still having problems with getting a particular thing, please let me know.

On the other hand, there are a lot of things you can do with construction lines that inferences can't do, like quickly get the midpoint between 2 points, do a perpendicular extension at an arbitrary spot on a curve instead of only at an endpoint, rotate the construction line by a particular angle, mirror points around a axis, get a point 1/3 of the way between 2 existing points without having a line already there, capture a distance and re-apply it from a different base point, capture a tangent/tangent line between 2 circles, .... and more... I mean it is actually a lot lot more feature rich for doing the kind of dynamic 3D drawing that you are asking about.

It may take some practice to gain a comfort level to access all of these functions, but they are all in there... There are a bunch of examples in the documentation here: http://moi3d.com/1.0/docs/moi_command_reference10.htm#constructionlines

- Michael