Am I drawing a rectangle or just 4 lines?


#1

@codeslayer2010

Thanks for that advice @sjdorst! … I see, so perhaps what is going on is that, even though I drew my shape with the rectangle tool (instead of a individual lines), SketchUp will view my rectangle as individual lines until I add them to a group? Is that right?

Not quite right. Realize that all geometry in SketchUp consists solely of lines and faces, faces being defined by closed loops of coplanar lines. So yes, although the Rectangle tool appears to draw a rectangle, inside SketchUp, you have created 4 coplanar lines - and you’ve created a face since those 4 coplanar lines form a closed loop.

The reason you need to double click before making the group or component is that the first click selects the face, and the second click close enough in time to be a double click extends your selection to adjacent geometry - the 4 lines that make up the rectangle. Thus you now have 5 pieces of geometry selected: the face and the 4 lines of the rectangle. When you then make them a group or component, you’re telling SketchUp two essential things:

  1. Treat this set of geometry as a unit. and
  2. Don’t make assumptions about how this new entity interacts with the rest of the model. (Snapping to other geometry or guidelines while moving, rotating or scaling don’t count - they have more to do with alignment than with geometry interaction)

From this point on, it will take an explicit action on your part for your group/entity to interact with the rest of the model. Actions such as “explode” - which undoes the grouping, or “join faces” which can merge two groups.

And while your group can be moved, rotated and scaled as a single unit, to change the underlying geometry of the group (or component) you have to first “edit group” (or “edit component”).

Yes, what I’ve just gone over are fine points. But then, I am, by nature, a nitpicker!

Hope this helps!


#2

And now to nitpick myself!

Yes, there ARE geometries other than lines and faces. Guide Points and Guide Lines come immediately to mind.

I’ve seen (and will soon myself use) Guide Points saved in components to mark the “ideal” point to choose when placing/moving an object so that it “snaps” reasonably. For example, it is often useful to add a guide point at the center of a circular base.

I’ve seen and used Guide Lines saved in components as an instructional tool. In my case,illustrating the symmetry within a component and how I used “change axes” on sub components to exploit these symmetries. I’ve yet to see a case where it makes sense to store a guide line in a component for production use.

Except a use case just occurred to me! Pipe and Fittings! If you want to create a piping system (with fittings), it could be of immense use to have a guide line stored with each component - so you can align different points around the same guide line, but separated in space (say for later insertion of a fitting) - especially with horizontal drain lines which shouldn’t be completely horizontal, but very slightly sloped. A guide line in the component would provide a snapping reference" that SketchUp could use instead of snapping to an axis or angle that happens to be very close to, but NOT exactly, the center line of the existing parts of the model.


#3

original post edited to correct spelling of “coplanar” - I’d originally spelled it “coplaner”. Thanks @jimhami42 for that nitpick in a private message!


#4

Hi SjDorst, useful explanation - many thanks. Can I ask the reverse question? How can I convert 4 lines all in the same plane and all meeting at 4 points to form what looks like a rectangle into a rectangle?

To add detail, this shape is not quite a rectangle. It is 2 arcs (2nd is an identical copy of the 1st). These are placed close on the same plane with a line connecting them top and bottom.

Many thanks


#5

To add a face to a set of coplanar edges that form a loop, you simply need to over-draw one of the edges and a face should form.
If it’s a very complex outline you might need to draw a few temporary ‘diagonals’ to create faces - these can then be erased to leave one face.
If the edges are not all coplanar they cannot support a single face.
If the edges define a coplanar ‘doughnut’ shape the face might form ignoring the ‘hole’.
To avoid this first over-drawn an edge on the 'hole to make a face, then repeat for the ‘ring’; you can then erase the face to leave the hole.
Another thing to be aware of is the face’s orientation.
You might need to reverse a face so it’s oriented to suit your needs - e.g. when you want to PushPull it later on…
The Style should have a distinct color set for the back-face so these are easy to see in View > Monochrome mode…


#6


#7

Thanks TIG, I’m back up and running again now. My example was quite straightforward however I’m also now prepared for much more complex examples. Bw Jon