SketchUp Drawing Tools Tutorial, Part 2 – Faces

In part one of my 2D SketchUp drawing tools tutorial (visit that tutorial by clicking here), we talked about using the 2D drawing tools to create lines. In order for us to move forward, I want to talk a little bit about the way models in SketchUp are made up.

Every model in SketchUp, when broken down to its basic building blocks, contains two types of objects. The first object type is lines. Lines are the objects we created in our first tutorial. At their most basic, these basically travel in one path between two points. They don’t have any area, they simply have a length. The other kind of objects that exist in SketchUp are faces. Faces are two dimensional areas that are drawn between lines. In order to draw a face, SketchUp must have at least 3 lines that create a closed shape on a 2 dimensional plane (meaning that the 3 lines must all intersect at some point).

Let me give you an example. Let’s say that we draw a triangle using the line tool. If I start with two lines, as shown below, then draw a third line between the two end points, what happens?

As you can see, as soon as this shape is closed, SketchUp automatically creates a face between these three points because it now has the 2 prerequisites required to create a face – at least 3 coplanar (meaning on the same plane) lines and a closed shape. The lines around the shape are called the “bounding edges,” because they are the lines that make up the outside boundary of the shape.

Let’s do a little experiment. What happens if you erase one of the bounding edges of this shape? As you can see in the image below, if you erase one of the bounding edges, we no longer have the prerequisites for a face in SketchUp, so the face disappears.

Occasionally, you’ll want to have groups of lines in SketchUp that are coplanar and intersect, but you won’t want a face between them. You can’t stop SketchUp from creating faces between coplanar lines, but what you can do is delete the faces. You can use the select tools to select a face in SketchUp just like you would a line. For example, let’s use the triangle that we drew up above. Close it back in so the SketchUp creates a face inside of it. Now, click inside the triangle on the face – what happens?

The face on the inside of your triangle develops a blue shading. This indicates that your face is selected.

Now that we have the face selected, press the “delete” key on your keyboard. This will delete the face between the bounding edges and just leave you with 3 lines.

The nice thing about SketchUp is if you delete this face, it isn’t gone forever. If you just re-trace one of the lines (draw over top of the existing line), then SketchUp will put this face back into your model.

Let’s say that for whatever reason, you decided that you wanted to divide this triangle in half into two triangles. If you take a line and draw it down the middle of the triangle, SketchUp automatically divides the face into two faces. SketchUp will always automatically divide a single face into multiple faces if you draw a line across it.

If you decide that you don’t want this face divided into multiple faces, you can go back and erase this line. SketchUp will automatically “heal” these two faces by merging them into one like they were before.

There’s one more thing about faces that I’d like to talk about. In SketchUp, faces have a front and a back side. This is why sometimes in your model you’ll have faces that show up as a dark color, and faces that show up as a light color. For basic modeling, this isn’t really a problem, but sometimes you’ll want uniformity in the way your model looks, or you’ll need to export models to rendering software, and if you don’t have materials on the right side of your faces, they won’t render properly.

The back side of a face shows up as a darker shade. The front side shows up as a white, lighter shade.

A good practice when working with your model is to always have the front side of your faces facing out. This is not difficult to do. If you right click on a face, you’ll see an option called “reverse faces.” This will cause the face to show the opposite of whatever face was showing before, so if your face was showing the back side, it will now show the front side, and vice versa.

In the next tutorial, I’ll show you how to draw shapes with the 2D drawing tools. You can read that tutorial by clicking here.

If you’re looking for other tutorials, check out my SketchUp tutorials section.

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