Designing in Three Dimensions

You are familiar with working in two axes on a computer screen. To represent a third dimension, another axis simulates an object moving toward you or away from you-coming out of the ground or moving underground is another way to describe the movement.

Examining coordinates

SketchUp uses a standard 3-D coordinate system of three axes called X, Y, and Z, as shown in Figure 32.3. Keep these ideas in mind as you learn to move around in 3-D space in SketchUp:

• Each axis can have both negative and positive values. In the program, the positive directions are shown as solid lines, while the negative directions are shown as dotted lines.

• Each axis uses a different color. Although you can’t see different colors in the figure, in the program the X axis is green, the Y axis is red, and the Z axis is blue.

• The point at which all three axes intersect is called the origin.

• The ground plane refers to the plane at which the X axis (green) and Y axis (red) lines run.

Figure 32.3: SketchUp uses a standard 3-D coordinate system, identifying positions on three axes.

Understanding entities

The simplest object you work with in SketchUp is a line, or edge. Lines are combined to form faces. Models are composed of edges, faces, and other objects or entities. The entities available for building a SketchUp model include:

• Line: A line, or edge, is straight and forms the connection between two points.

• Face: Faces are created automatically when three or more lines or edges on the same plane form a closed shape. Faces have a front side and a back side. SketchUp puts the front side of all faces on the outside of models.

• Arc: An arc entity is a combination of several line segments connected to form the curvature of the arc. The combined lines act as a single entity. An arc is drawn with the Arc tool.

• Curve: A curve entity is drawn with the Freehand tool. It is made up of several line segments connected together that act as a single line. A curve may be closed, meaning it begins and ends at the same point, or open, beginning and ending at different points like the examples shown in Figure 32.4. Both open and closed curves have lines, but only the closed curve has a face as well.

  
  Figure 32.4: A curve may be closed (left) or open (right).

• Polygon: Use the Polygon tool to draw a polygon entity. Polygons are made up of a radius and three or more sides.

• Rectangle, Circle: These entities are composed of several lines or edges using specific geometric relationships.

• 3D polyline: A 3-D polyline entity is like a curve in that it is made up of a number of lines that act as one but doesn’t affect a model’s geometry. A tracing of an imported drawing or hatched lines used to decorate a model are examples of a 3-D polyline.

• Group: Group entities are two or more entities of different types that are combined to make it simpler to perform operations like copying or moving.

• Component: Component entities are like groups in that they can be created from two or more entities of different types. A component is a named entity that you can reuse in any model, such as the window shown in Figure 32.5.

  
  Figure 32.5: A component is made up of different objects and can be saved in a library and reused, like the window.

• Construction line and Construction point. Use a Construction line or point entity as a drawing guide, such as the distance between the benches shown in Figure 32.6. Unlike other entities, a construction line or point is temporary, and can be hidden or erased. Construction lines and points are drawn with the Tape Measure tool. Choose Edit Construction Geometry and choose Hide, Unhide, and Erase to manipulate the construction lines or points in a drawing.

  
  Figure 32.6: You can specify length or distance using a construction line.

• Dimension: A dimension entity is a notation on a model that indicates the length or radius of an edge, such as the height of the shrub shown in Figure 32.7. The values shown move and update automatically as you make changes. Add Dimension entities to a model using the Dimension tool.

  
  Figure 32.7: Add the dimensions of an object, like the height of the shrub, on the model for reference.

• Surface: A curved surface, like the roundness of a cylinder, is made up of a number of faces. The higher the number of faces, the greater the appearance of a smooth, curved surface. The faces combined to create the smooth appearance are surface entities (see Figure 32.8).

  
  Figure 32.8: A curved surface is actually made up of many faces to create the smooth appearance.

• Image: An Image entity is a type of group made up of a face with an applied bitmap. An Image entity can be manipulated, such as scaled or rotated, but not made nonrectangular. Add an image by choosing File Import 2D Graphic, and selecting the image.

  Tip 

  SketchUp can use JPEG, PNG, BMP, TIFF, and TGA image formats.

• Text: Text entities are used to add annotations to a model. Text can be used as Leader Text, which has leader lines and is attached to a face, like the upper label in Figure 32.9, or Screen Text, which remains fixed at a specific location, like the lower label in Figure 32.9.

  
  Figure 32.9: Text can be applied using a leader line or added as a flat label to a model.