SketchUp For Dummies. Mark Harrison

FIGURE 3-10: Visual cues tell you when you’re drawing or moving geometry parallel to a drawing axis.

      FIGURE 3-11: The axes help you create 3D models on a 2D screen.

      Point inferences

      Generally, SketchUp’s inferences help you be more precise. Point inferences appear when you move your cursor over specific parts of your model. They look like little colored circles and squares, and if you pause for a second, a yellow label appears. The little green Endpoint inference, for example (which appears whenever your cursor hovers over the end of an edge), helps you accurately connect an edge that you’re drawing to the end of another edge in your model.

Figure 3-12 shows the point inferences that you use most often.

      FIGURE 3-12: Point inferences appear when you hover your cursor over key points and help you draw accurately.

      

In SketchUp, lines are called edges, and surfaces are called faces. Everything in your model is made up of edges and faces.

      Linear inferences

As you’ve probably already noticed, color plays a big part in SketchUp’s user interface, or the way it looks. Maybe the best example is in the software’s linear inferences — the “helper lines” that show up to help you work more precisely. Figure 3-13 illustrates the important linear inferences, and here’s a description of what they do:

       On Axis: When an edge you’re drawing is parallel to one of the colored drawing axes, the edge turns the color of that axis. In Figure 3-13, you see the On Red Axis inference.

       From Point: This one’s a little harder to describe. When a colored dotted line appears as you move your cursor, your cursor is “lined up” with the point at the other end of the dotted line. Naturally, the color of the From Point inference reflects the axis you’re lined up “on.” Sometimes, From Point inferences show up on their own, and sometimes you have to encourage them; see the section “Using inferences to help you model” later in this chapter for details.

       Perpendicular: When you draw an edge that’s perpendicular to another edge, the one you’re drawing turns magenta (reddish purple) unless it’s perpendicular to the red, green, or blue axes.

       Parallel: When the edge you’re drawing is parallel to another edge in your model, it turns magenta to let you know. You tell SketchUp which edge you’re interested in “being parallel to” by encouraging an inference. You can try this out by hovering over one edge and then starting to draw another with the Line tool.

       Tangent at Vertex: This one applies only when you draw an arc (using the Arc tool) that starts at the endpoint of another arc or an edge. When the arc you’re drawing is tangent to the other object, the one you’re drawing turns cyan. Tangent, in this case, means that the transition between the two arcs is smooth.

      FIGURE 3-13: SketchUp’s linear inferences help you align new geometry with existing geometry.

      

One of the most important inferences in SketchUp is one that you probably didn’t even realize was an inference: Unless you specifically start on an edge or a face in your model, you always draw on the ground plane by default. That’s right — if you just start creating stuff in the middle of nowhere, SketchUp just assumes that you mean to draw on the ground.

      Using inferences to help you model

      A big part of using SketchUp’s inference engine involves locking and encouraging inferences — sometimes even simultaneously. At first, these actions seem a little like that thing where you pat your head and rub your stomach at the same time, but with practice, they get easier.

       Locking inferences: If you hold down the Shift key when you see any of the first four types of linear inferences described previously, that inference gets locked — and stays locked until you release Shift. When you lock an inference, you constrain whatever tool you’re using to work only in the direction of the inference you locked.

       Encouraging inferences: Sometimes, an inference you need doesn’t show upon its own. When this happens, you have to encourage it. To encourage an inference, hover your cursor over the part of your model you want to “infer” from and then slowly go back to whatever you were doing when you decided you could use an inference.

The following example illustrates how you might lock and encourage inferences to draw a 3D model. In Figure 3-14, suppose that you want to draw a line on the blue axis that’s parallel to the right-rear corner of the block, in the same plane as the rear face and as tall as the block. Here’s how you might use inferences to help you:

      1  With the Line tool selected, encourage a From Point inference by hovering the cursor over the right-rear bottom corner of the block until you get an endpoint inference.

      2 Now slowly move your cursor to the right, away from that corner, to encourage a From Point inference. Do not click that corner.A dotted red line should trail from the pencil point back to the cube’s corner to indicate that you’re traveling parallel to the red axis. Press and hold the Shift key to lock the line in the red direction.

      3 Click to set the line’s starting point, release the Shift key, and then move the pencil up a bit, making sure it’s trailing a blue line.

      4 Press and hold down the Shift key to lock the line in the blue direction as you draw the line.The blue line inference becomes thicker to show that the line is locked in the blue direction.

      5 Move the cursor to the right-rear vertical edge of the cube while continuing to hold down the Shift key.

      6 When the inference to the Midpoint appears, click to set the endpoint of your new line.

      Behold! You have a vertical line that meets all the specifications!

      

Edges must lie in the same flat plane before a face can be made. Without inferences, it’s all too easy to create a series of edges that would do Escher proud. Even just three edges that appear to connect at their ends may not be connected when viewed from a different angle.

      FIGURE 3-14: Lock and encourage inferences as you draw new geometry in relationship to existing geometry.