Modifying a Shapes Geometry

Modifying a Shape’s Geometry

Whether you have modeled a cube or a spaceship, SketchUp defines anything you draw as geometry. There are a number of 3-D drawing techniques that can be applied to the geometry using tools in SketchUp. Most of the tools are based on the fact that you can add more faces and edges to existing geometry and then make changes based on those additions.

Dividing and healing

One SketchUp feature that makes modeling objects simple to do is the ability to divide an object’s structure, and then remove the dividing lines and restore the original if desired. The only tool required is the Line tool. SketchUp refers to the addition of extra edges and faces as dividing.

A complete cube drawn in SketchUp is shown in Figure 32.14. To add additional lines and faces, follow these steps:

1. Click the Line tool on the Getting Started toolbar.

2. Drag from an edge along one of the cube’s faces across the face. The inference engine shows you probable points, such as the midpoint.

3. Release the mouse when you place the line as desired. Continue adding other lines as desired.

4. Check the model shown in Figure 32.15. The front is split horizontally, and the face to the right is split vertically.

   
   Figure 32.15: You can easily add lines to create divided faces on a model.

5. To remove a dividing edge, click the Select tool on the Getting Started toolbar and then click the edge to select it, such as the vertical line shown in Figure 32.16. Press Delete to remove the line and heal the face of the cube.

   
   Figure 32.16: Remove edge lines to heal the face of the cube, returning it to its former state as a single face.

Using the Line tool to add extra edges divides only the faces on a cube, but doesn’t cut through the cube to make separate objects.

Extruding sections

Extrusion is a method of changing the geometry of an object by increasing or decreasing the dimensions in one plane or axis. The previous section that explains how to add lines to make a square into a cube is one example of an extrusion.

The Push/Pull tool on the Getting Started toolbar is an extrusion tool. Starting from a simple shape such as a 2-D square or circle, you can easily push or pull the shape into a 3-D cube or cylinder, like the examples show in Figure 32.17.

Figure 32.17: Use the Push/Pull tool to change a 2-D square to a 3-D cube (left) or a 2-D circle to a 3-D cylinder (right).

Using the Push/Pull tool isn’t restricted to a simple shape.

To use the Push/Pull tool to convert a shape from a simple cube to a more complex staircase object, follow these steps:

1. Click the Push/Pull tool on the Getting Started toolbar, and click one of the faces on the cube. The selected face shows an overlay of dots indicating it is active.

2. Drag to increase the size of a section of the cube.

3. Repeat the selecting and dragging of the cube’s faces.

4. Make adjustments as necessary by clicking an extruded face with the Push/Pull tool and dragging. The finished staircase is shown at the right of Figure 32.18. Where the original cube shown at the left of the figure has four faces specified, on the plane there are now four steps in the staircase.

   
   Figure 32.18: Use the Push/Pull tool to modify the faces on a cube (left) to a staircase configuration (right).

Working with sticky geometry

You can modify the geometry of an object by manipulating a face or edge, as shown in the previous examples using the Push/Pull tool. The SketchUp geometry is called sticky geometry, as moving an edge or face causes the objects attached to the edge or face to move as well.

Other tools can be used for modifying faces and edges on an object, and can be applied individually or in a sequence. Here’s an example using a variety of tools in sequence to create a finished model of a birdbath, complete with a base, column, and basin.

Drawing the base elements

The object begins with a simple rectangle, and then the Push/Pull and Offset tools are used to build the beginning of the structure.

1. Click the Rectangle tool and draw the starting square.

2. Use the Select tool to select the entire rectangle.

3. Use the Push/Pull tool to drag upward, completing the base of the object. In the example, the base is 4 feet square and 5 inches thick.

4. Click the Offset tool and drag it over the surface of the cube. As you drag, a rectangle is drawn using the same proportions as the original and centered over the original. Drag up/down and in/out to resize the new rectangle, as shown in the example in Figure 32.19.

   
   Figure 32.19: Add the second rectangle proportional to the first and centered over the first using the Offset tool.

5. Click the Push/Pull tool, and move it over the new rectangle. When you see the dotted lines that indicate the new rectangle is selected, drag upward to add a box shape on top of the original, as seen in Figure 32.20.

   
   Figure 32.20: Drag the second shape to form a box on top of the original base shape.

Rotating the top box

The next stage is to rotate the top of the rectangle to create a twisted, multisided effect for the top box. Although the tools can be used regardless of the view you show in the program window, it’s simpler to organize what you see to make the tools easier to understand and to use.

The example model is drawn using the default SketchUp positioning. To view the object from the top down, choose Camera Standard Top. The modified view shows the tops of the concentric boxes.

Note 

Depending on how you place the object initially, using the Top view may or may not show you the object directly.

To rotate the top box numerically, follow these steps:

1. Click the Rotate tool on the Getting Started toolbar, and move it over the objects on the screen. The tool displays a protractor, shown in Figure 32.21.

   
   Figure 32.21: It’s easy to understand how the Rotate tool functions when you view it directly.

2. Move the tool over the center of the upper box, viewed as the smaller square in the model when seen from the top. Click and drag with the tool to identify the object to which the tool is applied.

3. Type an angle for the rotation in the VCB and press Enter/Return. The example is rotated 345 degrees. The top view now shows some shallow triangle shapes on each side of the inner rectangle, as seen in the left image in Figure 32.22.

   
   Figure 32.22: After the rotation is applied, it’s difficult to see the effect from the Top view (left), but easily seen in the default view (right).

   Tip 

   You can type a value in the VCB or drag on the screen to rotate the protractor to the amount of rotation you want to add to the object, and click again to set the amount of rotation.

4. Reset the view to the default by clicking Home on the upper left of the program window below the toolbars. The sides of the upper box are now angled, resulting from rotating the top surface. Read the sidebar “Folding the Model” for more information.

Finishing the model

Even though the vertical faces of the column of the birdbath are now pairs of triangles, the top face is still a flat rectangle, and the rest of the model is built from the top face.

The finished birdbath model is shown in Figure 32.23.

Figure 32.23: The birdbath is a simple model that you can create using a few tools.

The final steps to complete the basic model include:

• Selecting the upper face of the top shape.

• Using the Offset tool to draw a square centered over the top shape and larger than the twisted column.

• Using the Rotate tool to reverse the rotation for the new square. The square is placed over the twisted column, but is not in alignment with the base. Setting the Rotation value to -345 degrees makes the new square drawn with the Offset tool match the orientation of the original base of the object.

  Folding the Model

  One of the basic rules in SketchUp is that a face must remain planar, or parallel, to a plane at all times. Rotating a face on an object causes warping. SketchUp automatically twists and folds the faces of the object to make sure you aren’t violating the rules. The example shown in the chapter is typical of the way the program compensates for rotation. Each face of the box, originally a rectangle, is split into a pair of triangles that allow the top to rotate without violating the planar face rule.

• Using the Push/Pull tool to pull up the sides of the birdbath’s basin, leaving the basin space the size of the column.

If you want the basin of the birdbath to be larger or smaller than the column’s dimensions, use the Offset tool to add one more square between the column and the square that defines the birdbath’s margins.

Note 

If you want to resize any of the objects, select the object and choose Tools Scale to open the Scale tool. Move the mouse over any of the resize anchors to read the tooltips offered by the inference engine, and drag any of the resize anchors to change the scale.

Combining and moving objects

SketchUp helps you build complex geometry using a set of four processes that include:

• Intersecting two forms

• Defining new edges where the objects intersect

• Redefining the geometry

• Deleting extra lines and faces from the combined geometry

The birdbath model can be developed into a postmodern sculptural object using more tools and program commands.

Follow these steps to add some cutout details to the model:

1. Click the Rectangle tool on the Getting Started toolbar, and draw a rectangle on the screen. Click the Push/Pull tool, and extrude the rectangle to make a box.

2. Click the Select tool to drag a marquee around the box to select all its elements.

3. Click the Move tool on the Getting Started toolbar. The Move tool repositions an edge, face, or an entire object depending on the selection. In the example, the Move tool affects the entire box as it is entirely selected.

4. Drag the block from its drawing location on the screen to intersect with the column of the bird-bath. Release the mouse once the block is positioned as shown in Image A in Figure 32.24.

   
   Figure 32.24: Use other program tools to make cutouts in the original model.

   The front face of the box is protruding through the face of the birdbath’s column. Notice that areas that intersect don’t display edges.

5. Choose Edit Intersect with Model. The geometry of the block intersects with the geometry of the column of the birdbath. On the model, the areas of intersection now show edges, as seen in Image B in Figure 32.24.

6. Click the Eraser tool on the Getting Started toolbar and click faces and edges in the intersected areas to remove them, as shown in Image C in Figure 32.24. New faces and edges are shown within the structure based on the intersected areas.

7. Add more cutouts to change the geometry as desired. In the final model, shown in Image D in Figure 32.24, another block has been used to cut out another area of the column.

Note 

Several other drawing and manipulation tools are also available. Please experiment with the tools, and refer to the SketchUp Help files and tutorials for more information.

Mirror Images

Many objects have mirrored halves. That is, a table has a left and a right half, as does a television. Instead of drawing the complete object, draw one half and create a group. Then copy and paste the group to the model. Right-click/Control-click to open the shortcut menu and choose Flip Along. Select the direction or axis in which you want the object to flip. Position the second half to match the first.