16. Learning Modeling Techniques and Structures

Open the database radio.g that you created in Lesson 2. In the Command Window, use the ls command to list all the contents of your radio. It should read as follows:

Now what does this list really contain? Parts to a model radio? Not really. What the list actually comprises is just a collection of shapes (which we have hinted at by using a .s suffix) that (1) do not have material properties, and therefore (2) do not occupy space.

So our first order of business is to identify the major parts of the radio so we can properly define the regions. So far, our choices are fairly simple. The radio basically consists of (1) a body, which houses the speaker and all of the internal parts; (2) an antenna; (3) a volume control knob, and (4) a talk button. These should be our four regions.

Most of these shapes were fairly straightforward to create, with each item consisting of just one or two primitive shapes. However, if we think of the radio as a real-world object, the body of the radio is actually more complex than just a solid box with a few shapes glued to its surface. (Remember that all objects are solid unless constructed to be otherwise.) Therefore, let’s start with the main component of the radio-the body.

If we think about it, the body of a radio is actually a hollow case. So, the first thing we need to do is hollow out the case’s interior to make room for internal components. To do this, we can use the inside command to create a shape, which we’ll call cavity.s:

inside body.s cavity.s 1 1 1 1 1 1 Enter

Now, we’ll make a region called case.r and define it as what’s left of body.s after cavity.s has been subtracted out. The command should look like this:

r case.r u body.s - cavity.s Enter

With our case now made, we can proceed to cut several holes through this structure to accommodate the antenna, the volume control knob, and the talk button. To do this, we must subtract the three shapes from the case as follows:

r case.r - ant.s - knob.s - btn.s Enter

Finally, we need to "glue" the lip around the speaker to the case’s front face by typing

r case.r u spkr.s Enter

Our body is now finished. Note that an experienced modeler would probably have combined the preceding three Boolean functions into a single command as follows:

r case.r u body.s - cavity.s - ant.s - knob.s - btn.s u spkr.s Enter

If we were to raytrace case.r at this point, we would see the following:

Note the hole for the antenna in the top of the case and the hole for the talk button on the side of the case. We will now fill these holes with their respective components.

Making the talk button is simpler than making the case. The button consists of the union of two primitive shapes. To make them into a region, type

r button.r u btn.s u btn2.s Enter

The volume knob and antenna are even simpler. They are single primitive shapes that can be made into regions by typing

r knob.r u knob.s Enter

r ant.r u ant.s Enter

Now let’s take all of the regions we have made so far and gather them into an assembly (or group) combination called radio.c so that we can keep all of these parts together. There are several ways to do this. One way would be to use a similar method to the one we used to make the regions:

comb radio.c u case.r u button.r u knob.r u ant.r Enter

A shortcut, however, would be to use the g (group) command as follows:

g radio.c case.r button.r knob.r ant.r Enter

Unlike the comb command, the g command assumes that all of the items specified will be unioned together, and so no Boolean operators need to be specified.

A final improvement would include using the database name wildcard *.r to quickly and easily specify all of the regions in the database:

g radio.c *.r Enter

If we now tree radio.c, we should get the following output in the Command Window.

Thus far, the objects we have created have no material properties other than the gray plastic that MGED assigns by default to any object without assigned material values. Now let’s improve our design by assigning other material properties to the components.

We’ll give the antenna a realistic look by opening the Combination Editor, choosing ant.r from the drop-down Name menu, selecting mirror from the drop-down Shader menu, and clicking on Apply.

We’ll let the other components remain with the default plastic, but we’ll assign them different colors. With the Combination Editor still open, select case.r from the drop-down Name menu, select the magenta option from the drop-down Color menu, and then click Apply. Use the same method to assign the volume control knob (knob.r) a blue color. For the talk button (button.r), let’s keep it gray by leaving the default values in place. The design should appear similar to the following when raytraced in Underlay mode:

As we look at our radio now, we can see that the antenna looks a little bit like a straw. In reality, it should have a small cap on the end so that we can raise and lower the antenna. We can approximate this shape by creating an ellipsoid (which we’ll call ant2.s) and unioning it in with the rest of the antenna as follows:

in ant2.s ell1 2 2 94 0 0 1 3 Enter

r ant.r u ant2.s Enter

Our radio is looking more and more realistic; however, it is still just a hollow shell. Let’s further improve it by making a circuit board to go inside the case. To do this, type:

in board.s rpp 3 4 1 31 1 47 Enter

r board.r u board.s Enter

Let’s give the board a green semi-shiny color. The easiest way to do this is via the Combination Editor, but this time let’s use the Command Line approach. Type:

mater board.r "plastic sh=4" 0 198 0 1 Enter

Diagrammed, this command says to:

Finally, we’ll include the board with the rest of the components in radio.c as follows:

g radio.c board.r Enter

Our radio should now look like the following:

In addition, the tree for radio.c should now look as follows:

Now, what would happen to the circuit board if we were to raytrace the radio at this point? It would disappear because it lies within the case. So how can we make the circuit board visible outside of the case?

There are two common ways to do this: a transparent view and a cutaway view. Each method has its advantages and disadvantages. With the transparent view, the Boolean operations remain unchanged, but some of the material properties of the "outside shell" are altered to better view interior parts of the model. With the cutaway view, the material properties remain unchanged, but some of the Boolean operations are altered to remove parts of the model that are obstructing our view of other parts. We will try both ways to view the inside of our radio.

Different Approaches to Creating Specialty Models

An important point to note here is that the transparent and cutaway views are specialty models. They are similar in nature to items a manufacturer might make for special purposes. For example, an automobile manufacturer makes cars for everyday use, but also makes modified versions for display at certain events. The body panels might be replaced with a transparent material or be partially cut away to reveal interior components.

Good modeling practice follows the same pattern. The actual model of an item should not have to be changed in order to create a specialty view of it. Instead, a modified version of the item should be created. Thus, the modeler will not have to worry about remembering to return the model to the original condition after its special-purpose use, and the modeler can also retain the "display model" for future use.

There are two common approaches to making these specialty models: First, the modeler can copy the original and replace components with modified versions. Second, the modeler can create new, unique parts from scratch and construct the modified item. The method chosen is a matter of personal choice and is usually determined by the extent of the modifications being done and the complexity of the original object.

As shapes are added in a design, the modeler often finds that the structure or association of components needs to change. Thus, we should pause at this point and consider how our radio is structured. While there are many ways to structure a model, two common modeling categories are location and functionality. For our radio, we have so far grouped everything together under the general category of Radio, as shown in the following:

If we wanted to categorize our components according to location, however, we might structure the model as follows:

If we wanted to define our components according to functionality, we might structure the model another way. For instance, to repair an actual radio, we would open the case, take out the circuit board, fix it, and put it back in. When taking out the board, however, the knob and button would probably be attached to it in some way, and so they too would need to come out. Accordingly, our structure should be changed as shown in the following diagram to associate the knob and button with the circuit board.

To accomplish this restructuring according to functionality, create an assembly called electronics.c to hold these components together. Type:

g electronics.c board.r knob.r button.r Enter

Of course, we now need to remove board.r, knob.r, and button.r from the radio.c assembly so that when electronics.c is added to the radio.c assembly, we won’t have the knob and button included twice in the model. To do this, use the rm (remove) command:

rm radio.c board.r knob.r button.r Enter

and then union in the electronics assembly:

g radio.c electronics.c Enter

Now the tree for radio.c should appear as follows:

Now let’s remake our cutaway view. This time, let’s do what we discussed earlier and make the cutaway remove material from only the case, showing all the other components.

First, we need to get rid of the old radio_cutaway.c, which was based on our previous structure. To do this, type

kill radio_cutaway.c Enter

and then remake the combination by typing

comb radio_cutaway.c u case.r - cutaway.s u electronics.c u ant.r Enter

Now when we Blast the display and raytrace radio_cutaway.c, we should see the following:

In this lesson, you: