3. Using the Insert Command in MGED to Size and Place Shapes

Create a new database and name it shapes.g. Title your database myShapes.

Begin by making the Command Window active (usually by clicking anywhere in the window). Then, at the MGED prompt, type in the command:

make sph1.s sph Enter

As noted in Lesson 1, this command tells MGED to:

A sphere shape has now been created, and a wireframe drawing should appear in your Graphics Window.

To make the rcc from the Command Window prompt, type:

make rcc1.s rcc Enter

Your Graphics Window should now display a large rcc that, from the default view of az35, el25, looks as if it intersects the sphere you previously created.

Using the make command is a fast and easy way to create a shape; however, most models are going to require shapes that have specific parameters, such as height and radius. So, a more precise way to create these shapes is to use the in (insert) command.

Begin by making the Command Window active (usually done by clicking anywhere in the window). Then, use the Z (zap) command to clear the Graphics Window. You are now ready to create a sphere using the in command. At the MGED prompt type:

in sph2.s sph Enter

MGED will respond with:

Enter X, Y, Z of vertex:

You must tell MGED where to position the vertex (center) of your sphere in space. Type at the MGED prompt:

4 4 4 Enter

Your sphere will now be placed at (x,y,z)=(4,4,4), as measured in millimeters. Notice that the numbers are separated by spaces followed by the ENTER key. MGED will now ask you to:

Enter radius:

Type in:

3 Enter

The radius of your sphere will be 3 mm. The following is the dialog that should appear in your Command Window (including the appropriate responses).

mged> in sph2.s sph

Enter X, Y, Z of vertex: 4 4 4

Enter radius: 3

51 vectors in 0.000543 sec

The last line of this dialog is simply a record of the computer’s speed in drawing the shape. It has no real usefulness to the user at this point.

A sphere has now been created, and a wireframe drawing similar to the one created using the make command should appear in your Graphics Window.

To make the right circular cylinder, type at the Command Window prompt:

in rcc2.s rcc Enter

MGED will ask you to enter values for x, y, and z of the vertex (where you want the center of one end of the rcc placed in space). Type:

4 4 0 Enter

Be sure to leave spaces between each of these numbers.

MGED will now ask you to enter the x, y, and z values of the height (H) vector (i.e., how long you want the rcc to be). Type:

0 0 4 Enter

The last value you will need to enter is the radius of the rcc. Type:

3 Enter

The dialog in the Command Window for the creation of the rcc should look like this:

You should now have new versions of the sphere and rcc shapes. Notice how these two shapes compare in size to the first two you created. The rcc is now in proportion to the sphere and is placed in space off to the left in your Graphics Window. By specifying the dimensions of the shapes and their locations in space, you were able to create the model more precisely.

Another way to use the in command is to combine all of the required information on one line. Once you become familiar with using the in command, you will probably prefer to use this method as it allows you to input all the parameter values more quickly.

Clear the Graphics Window by using the Z command. Now make another sphere by typing after the MGED prompt:

in sph3.s sph 4 4 4 3 Enter

The meaning of this longer form of the command is:

The meaning of this command is:

When you are first starting to use MGED, if you want to use the Command Window rather than the GUI, you may want to make yourself some blank, combined-command forms for each type of primitive shape you will be creating. This can speed up the design process and help remind you of which values must be entered for each shape. A form for the sphere might be:

A Combined-Command Form for the rcc might be:

You may have noticed that each time you have created a sphere, or rcc, you have given it a different name. MGED doesn’t care what name you give a shape, but you will find as you develop models that it helps to have some formula, or conventions, when naming shapes. Note also that each name must be unique in the database, and for BRL-CAD releases prior to 6.0, names are limited to 16 characters in length.

In this lesson, we sometimes assigned names to the shapes based on their shape type and the order in which we created them. We did this because the shapes had no real function, except to be examples.

When you create real-life models, however, you will probably want to assign names as we did for the radio component names, which were based on their functions (e.g., btn for button, ant for antenna, etc.).

If you work with more experienced modelers, check with them to see what set of conventions they use. If you work alone, develop a set of naming conventions that works for you and then use it consistently.

Practice viewing your new shapes using the View menu. Manipulate your view using the various mouse-key combinations identified in the previous lesson.

If you wish to quit MGED, at this point, type either the letter q or the word quit after the Command Window prompt and then press ENTER. You may also quit the program by selecting Exit from the File menu.

In this lesson, you: