Why snapping works (and why it sometimes doesn’t)

The prompts and the description of how the middle button mouse work in the help files gives us a clue.

It starts with the understanding of what we are working with – in a CAD program it is simple. Regardless of what we call stuff when we create it and subsequently use it, we are dealing with points that define lines and lines that define plane boundaries.

That’s it! We give the lines and planes attributes, but they are still just a bunch of points, lines and planes.

So when you are prompted to ‘snap’ the start or end point of a line to the start or end point of an existing line, you are telling the software to use the start/end point of the line, and not create a new point. So you can have three points and two lines and ‘sound’ geometry.

Indeed, if you verify a line (Tools > Verify) it shows you the X,Y,Z coordinates of the start and end point of each line;

So when using the [O] button function, ‘snap’ the reference start point at the end of the line and it works perfectly.

If your middle mouse button is 'dodgy', as sometimes a scroll wheel mouse can be, use the Shift key + left mouse button. That always works to ‘snap’ the intersection of a couple of lines.

Certainly you must ensure that the ‘pick box’ must cover the corner you are trying to snap to:

Note that you cannot just bang the curser anywhere along a line and try to ‘snap’, as there are no points along a line – only at the ends. That is why we use the Reference [O] function, to establish a reference point relative to a known corner/end point.

One more point, when you define an outline initially, the outline is a construction outline only – no geometry exists yet, so nothing (no roof geometry) to snap to at that stage, and you shouldn’t be snapping then anyway. You only snap to existing roof geometry.