Force "line extension"-like behaviour in Illustrator

Question

When having a single line in Illustrator and you manipulate one of the anchor points, Illustrator helps you a little by giving you a smartguide that aligns the anchor point along the current trajectory of the line.

Now I was wondering if this is also in some way possible with more complex shapes like a skewed rectangle or in my case a custom shape in isometric perspective which I would like to prolong while keeping the angle the exact same (rather than eyeballing it).

Thanks!

Answer 1

For line extension to work on a rotated rectangle, it must still be designated as “Rectangle” in the layers panel.

Rectangles become Paths if you skew them, or unite them with another object. In that case, add a Rectangle, rotate it to the same angle, and centre the two. The line extension will use the Rectangle for the constrain angle.

An ellipse will also work. And this may be better than adding a rectangle that is not part of the artwork.

Answer 2

It's possible to do this with a path, selecting the path, setting a transform reference point and increasing the width with Constrain Width and Height Proportions checked.

Not with a shape, unless it is made with separate paths:

But you can always make a wireframe 3D tube and increase the depth:

Answer 3

It's a bit kludgy, but in the past I've performed similar actions by doing the following:

1. Use the Direct Select tool to select a single point from within the set that you want to move.
2. Transform that point manually (drag), following the Line Extension smart guide.
3. Use Lasso or other selection method to select the remaining points that you want to move.
4. Repeat the transform using Transform Again (Ctrl+D or Cmd+D)