How to align objects without square corners

This is driving me nuts. When moving objects that have square corners or centerpoints I can align them by clkg the point on the object being moved then clkg the point on the object being move to - perfect.
But I often have an object I want to move to that has a round edge, no corner. How do I snap to something like this. eyeballing it does not work very well.

I tried using the group edge, but SU doesn’t seem to like to to that in that it is very difficult to select it and when it does it is not very accurate or consistent.

You can use construction lines or point to get some reference for the inference system. Or you can use plugins like

Remember, there are no “round edges”–everything is made of flat facets, which have straight edges and endpoints and midpoints, so there are all kinds of things to grab onto and align with other things. You just have to turn on hidden geometry to see and use them (View > Hidden Geometry).

Also, keep in mind that you don’t have to move point-to-point. You can align two objects along one axis at a time, and when you break it down into steps, you can almost always find a likely alignment point for each step.


this is true but other than the bounding box for a group there is no “edge” that will allow me to attach another object to the face and have the top of both on the same plane AND the object won’t snap to a bounding box line.

So take 2 boxes, radius a top edge of one box and move the a box so that the radius edge face side of one box is butt up to a face of the other box and the tops are on the same plane. Then tell me how u did it.

There’s this old trick


It’s fairy basic, but if you hit one of the arrow keys you will toggle a lock to that axis when moving stuff*. And if you can get the object moving in the right direction you can hold [shift] to lock to that direction (while it’s depressed).
If it’s locked to a specific direction, then you can click on any reference point in the drawing and it will move in that direction until it hits the inferred reference.

Also remember that you don’t need to move it all in one go: it’s often easier to move something directly to a reference point, then move it away again while constraining rather than constraining while trying to find a specific point of reference.

(* Note: if you lock with arrow keys, it will unlock when you zoom/pan but not re-set the arrow key toggle, so you will have to hit the arrow key twice after the zoom/pan to get it back on)

That’s almost too easy. Just start with an On Face inference on the box to be moved and snap it to a corner. Thus:

Then you can raise one box and inference the top face of one to the top face of the other: