Using Hierarchical Grouping
The ability to properly use hierarchical grouping and set rotations are crucial for effective design and animation. The Hierarchical Grouping tutorial provides you with the basic knowledge to set up and properly use hierarchical groups and to define and change rotation points and set rotations.
Creating a Primitive Leg
Rotation points are important for pivoting parts of a model. They tell the program the location of the point around which segments of a model rotate. For example, if you have a robot arm, you would set a rotation point at the elbow so that when the lower arm rotates, it will remain attached at this pivot point.
NOTE:To understand the use of rotation points as well as hierarchical grouping, you will create a simple robot leg using primitives. To start:
- Create a new document.
- Select a color from the color swatch and go to the primitives and select a cylinder.
- In the Cylinder info palette at the top of your screen, click in the square to the left of the Depth: to make it active with an x.
- For depth, type 6.
- Click in the Radius box to make it active with an x and type 1 for radius.
- Click in the Top window and drag a little to the left until the cylinder appears. You should now have a cylinder.
- Go to the Groups palette and double click the name Cylinder 1.
- In the Object/Group Information box, next to Name, type UprLeg
NOTE:
If you plan to reshape the primitive, you need to:
- Click the Convert to Spline Mesh button. Click OK to exit the box. Notice the name of the object has changed to UprLeg in the Groups palette.
- Click on the name UprLeg in the Groups Palette to select the object.
- Press S on the keyboard to get the arrow cursor.
- In the Front view, click on the cylinder and start dragging it straight down. Before you let go of the mouse button, press the Option and Shift keys down. This will make a duplicate and constrain the movement of the object to a straight line.
- Move the duplicate cylinder straight down until it butts up to the first one (Illustration 30).
- Go to the Groups palette and double click the duplicate object named UprLeg.
- In the Object/Group Information box, next to Name, type LwrLeg.
- Click OK to exit the box.
Illustration 30 - Duplicating the cylinder
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NOTE:
Make sure that you can see the cylinders in the Top window and then:
- Place the cursor in the middle of the oval in the Top window and press the Spacebar key down once. This locks it on the Z and X axes.
- Select the pyramid object from the primitives. Type the following settings in the pyramid info palette at the top of your screen.
- For Sides type 3.
- Click in the Height box to select it and type 2.
- Click in the Width box to select it and type 2.
- Click in the Depth box to select it and type 6.
- Go to the Right window with the pyramid tool and click at the point where the bottom cylinder ends and drag to the right. This will make the foot. Move the triangle so that it is in the right position for a foot (Illustration 31).
Illustration 31- The primitive leg
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- In the Groups palette, double click the name Pyramid 1 and rename it *Foot.
Creating Hierarchies
- Now, it is time to organize the leg into hierarchies. In the Groups palette, while holding the Shift key down, select both the LwrLeg and Foot.
- Press Command G to group the two together. Name it *LwrLeg and click the Add button.
- You should now see a folder icon next to the name *LwrLeg. If you click the triangle next to the folder it will open it to reveal the contents.
- Click on the triangle again to close the folder.
- Shift select the object named UprLeg and the folder named *LwrLeg and press Command G to group them.
- Name it *Leg and click the Add button.
Tip: All the leg parts are now in one folder named *Leg. The reason you put an asterisk * next to the names of the folders is to identify which parts are going to have rotation points. The foot should have an asterisk in front of its name because it will also be assigned a rotation point.
- Click on the triangles next to the folders in the Groups palette to open them. Your Groups palette should look like Illustration 32.
Illustration 32- Leg Hierarchy
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Setting Rotation Points
The first step is to set a rotation point for the entire leg. Using the Spacebar, you will set a depth in two windows to identify the location of the rotation point in 3D space.
- In the Front view, place your cursor in the middle and the top of the leg and press the Spacebar. This will lock the location of the Y and X axes.
- In the Right view, place your cursor in the middle and the top of the leg and press the Spacebar. This will lock the location of the Y and Z axes.
NOTE:You should see vertical and horizontal dotted lines that intersect in the area where you want the rotation point.
- In the Groups palette, double click the folder with the name *Leg.
- In the Object/Group Information box, click on the arrow under the Rotation Point heading until you see a pop-up menu.
- Select 'Lock' Value from this pop-up menu (Illustration 33).
Illustration 33- Setting the Rotation Point
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- 'Lock Value' tells the program to set a rotation point at the location in which you locked using the Spacebar key.
- In the Front view, place your cursor in the middle of the two legs (where the knee would be) and press the Spacebar. This will lock the location of the Y and X axes.
- In the Right view, place your cursor in the middle of the two legs and press the Spacebar. This will lock the location of the Y and Z axes.
NOTE:You should see vertical and horizontal dotted lines that intersect in the area where you want the rotation point.
- In the Groups palette, double click the folder with the name *LwrLeg.
- In the Object/Group Information box, click on the arrow under the Rotation Point heading until you see a pop-up menu.
- Select 'Lock' Value from this pop-up menu (Illustration 33).
- In the Front view, place your cursor where the top of the foot meets the bottom of the leg (at the ankle) and press the Spacebar.
- In the Right view, place your cursor where the top of the foot meets the bottom of the leg (at the ankle) and press the Spacebar.
- In the Groups palette, double click the object with the name *Foot.
- In the Object/Group Information box, click on the arrow under the Rotation Point heading until you see a pop-up menu.
- Select 'Lock' Value from this pop-up menu.
NOTE:You have just completed setting all the rotation points for the entire leg. The next step is to check the location of the rotation points.
- Go to the Edit menu and select Preferences...
- Click the Screen button on the left and select 5 Pixels for Vertex Options. Click OK.
NOTE:This will insure that the rotation point is easier to see.
- Go to the Windows menu, select Palettes Statistics.
- In the Statistics box click in the square next to Show Rotation Point (Illustration 34).
Illustration 33- Setting the Rotation Point
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NOTE:You can now leave the Statistics box open or close it.
- In the Groups palette, click on the folder named *Leg to select it.
Now, look at your different views. You should see a point at the location that you set for the rotation point.
NOTE:You can adjust the rotation point by clicking and dragging it in any of the windows. You will probably need the magnifying glass to see the rotation point.
- Click on the folder named *LwrLeg and adjust the rotation point.
- Click on the object named *Foot and adjust the rotation point.
Testing the Rotation Points
- In the Groups palette, select the *Lwr Leg folder and select the 2D Rotation Tool from the tool palette.
- In the Rotation tool Info Palette at the top of your screen next to Anchor: click the pop-up button and select Rotation Point. This tells the program to rotate the *LwrLeg around the rotation point.
- In the Front window click and drag to the left and you should see the lower leg and foot rotate together as if the leg were bending at the knee.
NOTE:Try rotating the *Leg and the *Foot. Later on, when you animate, you will see how useful rotation points are.
Duplicating and Mirroring the Leg
Now that your leg has rotation points, you can duplicate it so that you have 2 legs. The duplicate will have the same rotation points that you already set on the first leg.
- Close the folder named *Leg and select it in the Groups palette.
- Press Command W to duplicate the *Leg folder.
- Press the S key to get the arrow cursor and move the duplicate leg to the right in the Right view.
- Press the Shift key down while moving the duplicate leg to constrain its movement to a straight line.
NOTE:Normally, your leg would not be symmetrical so that you would have to mirror it after duplicating the leg. Even though mirroring will not make much difference with this simple leg, nevertheless you should do the following to learn the procedure.
- Select the Mirror Tool. In the Mirror Tool Info Palette at the top of your screen set the following.
- For Anchor: select Center Object(s) from the pop-up button, click in the Incremental Degrees box to x it and type 180 for degrees.
- Make sure the duplicate leg is selected in the Groups palette and click in the Right window and drag in a clockwise direction until you see the leg flash briefly. This flips the leg to mirror it.
NOTE:In the future, if you are having trouble mirroring an object try making the view of it smaller. Sometimes the program needs the extra space around the object to flip it.
Review Assignment
To build on what you just learned, perform the following suggested steps.
- Follow the instructions to model a human leg. Feel free to add a pelvis or lower abdomen area.
- Arrange all the parts by grouping them hierarchically.
- Set rotation points for the leg and the lower leg and the foot.
- Duplicate and mirror the entire leg folder.
- Select the two leg folders and the pelvis in the Groups palette and group them (Command G). Name the folder *Body and assign it a rotation point at the groin.
- Save the Modeler file.,
NOTE:In a later tutorial, you will animate the legs.