Search form

'Poser 7 Revealed': Use Inverse Kinematics

In the latest excerpt of Poser 7 Revealed, Kelly L. Murdock explores how to create a new IK chain.

All images from Poser 7 Revealed: The e frontier Official Guide by Kelly L. Murdock.

This is the next in a new series of excerpts from the Thomson Course Technology book Poser 7 Revealed: The e frontier Official Guide. In the next few months, VFXWorld readers will develop the skills needed to create, render and animate scenes and projects using the amazing tools offered by Poser 7. We will offer step-by-step tutorials for each task, followed by projects that allow readers to apply each new skill.

What You'll Do

In this lesson, you learn how to create a new IK chain.

Kinematics is the physics behind the movement of linked objects. Bone structures are a good example of a set of linked objects that can be defined using kinematic solutions. For example, because the shoulder is connected to the arm bones, which are connected to the hand, you can use kinematic equations to determine the position of the hand as the shoulder moves. Inverse Kinematics works backwards by solving the shoulder's position as the hand is moved.

The benefit of Inverse Kinematics is that it is often easier to animate characters by placing their hands and feet than placing their hips and shoulders. For example, imagine a character walking across the floor and reaching for a door handle. To animate this sequence by moving only the upper thigh and upper arm bones would be difficult, but with Inverse Kinematics enabled, you can position the feet for the steps and the hand for the door handle and the remaining body parts just follow.

[Figure 1] Hierarchy Editor (left). [Figure 2] IK chains in the Hierarchy Editor (right). 

Working with Inverse Kinematics

When Poser first loads, select the default figure's Left Thigh object and try to move it with the Translate/Pull tool. The upper thigh element might twist a little, but because it is part of the IK chain, it won't move out of place unless the end of the IK chain, the foot, is moved.

Quick Tip: You should enable and use IK if you need to place the end of an IK chain such as a hand or a foot in a specific location, but for general body movement and poses, you can disable IK.

Now try disabling IK and moving the upper thigh element again. This time the upper thigh moves easily and the foot moves along with it. The trick is to learn when to use IK and when to disable it.

In order for Inverse Kinematics to work, you need to select a parent object (the root object) and one of its children objects (the goal object) connected in a chain. All the bones between these two selected bones are collectively called an IK chain. You can select IK chains by using the Hierarchy Editor. This dialog box is opened with the Window, Hierarchy Editor menu command. All IK chains for the current figure are displayed at the bottom of the Hierarchy Editor, shown in Figure 1.

Viewing IK Chains

All existing IK chains are listed at the bottom of the Hierarchy Editor, as shown in Figure 2. Each IK chain lists all the elements included in the chain from root to end element, called the goal. To the left of each IK chain is a check box that you can use to enable and disable the selected IK chain.

Creating New IK Chains

You can create new IK chains using the Hierarchy Editor. These new IK chains can be created for manually imported characters, for new types of figures such as the tail of an animal, or to add an attached prop to an existing IK chain. To create an IK chain, select the IK Chains title in the Hierarchy Editor to make the Create IK Chain button active. Clicking the Create IK Chain button opens a dialog box where you can give the new IK chain a name. The newly named IK chain appears at the bottom of the Hierarchy Editor. You can then drag and drop elements of the chain onto the new chain name. The first element under the new IK Chain title is the root element and the last one is the goal. The goal element is marked with the word goal is parentheses.

You can create new IK chains using the Hierarchy Editor. You can create new IK chains for manually imported characters, for new types of figures such as the tail of an animal or to add an attached prop to an existing IK chain. To create an IK chain, select Window, Hierarchy Editor to open the Hierarchy Editor. Scroll to the bottom of the Hierarchy Editor dialog box and select the IK Chains title. This makes the Create IK Chain button active. Clicking the Create IK Chain button opens a dialog box where you can give the new IK chain a name. The newly named IK chain appears at the bottom of the Hierarchy Editor. You can then drag and drop elements of the chain onto the new chain name. The first element under the new IK chain title is the root element and the last one is the goal. The goal element is marked with the word goal in parentheses.

Note: Newly created IK chains are also listed in the Figure, Use Inverse Kinematics menu command.

Enabling Inverse Kinematics

Inverse Kinematics can only be enabled for a set of connected body parts referred to as a kinematic chain. For Poser, you can enable Inverse Kinematics (IK) for four kinematic chains -- right and left arms and legs. IK is enabled by default for the legs, but not for the arms. You can enable or disable IK using the Figure, Use Inverse Kinematics menu command. When enabled, a small check mark appears next to the menu.

[Figure 3] Default chain break icons (left). [Figure 4] New tail IK chain (right). 

Using the Chain Break Tool

IK chains aren't the only elements that have control over other body parts. Actually almost all body parts are connected and can influence one another. If you drag an arm element far enough, the torso will move along with it, but you can use the Chain Break tool (L) to prevent the movement of connected elements.

If you select the Chain Break tool, several chain break icons appear on the figure in Document Window, as shown in Figure 3. These icons mark body parts that are prevented from moving with adjacent elements. By default, the head, hip, right and left buttock elements have a chain break icon on them. This means that the head moves independently of the torso and the torso moves independently of the legs.

If you click an element with the Chain Break tool, you can place or remove these icons. For example, if you click the right and left collar elements, moving the arms will have no effect on the torso.

Caution: The chain break icon for the hip cannot be removed.

Create an IK Chain

1. Select File, Open and open the Lion.pz3 file.

This file includes a loaded lion figure.

2. Select Window, Hierarchy Editor to open the Hierarchy Editor.

3. Scroll to the bottom of the Hierarchy Editor and select the IK Chains title. Then, click the Create IK Chain button at the bottom of the dialog box.

4. In the Set Name dialog box that appears, type the name, Tail and click OK

5. Scroll back up in the Hierarchy Editor and select and drag the Tail 1, Tail 2, Tail 3, Tail 4 and Tuft elements and drop them on the newly created Tail IK Chain title.

6. Reorder the tail elements so they appear in order with the Tuft element designated as the goal.

7. Click the square box to the left of the Tail title to enable the IK chain. Then, select and move the tuft element.

As the tuft element is moved, the other members of the IK chain are also moved, as shown in Figure 4.

8. Select File, Save As and save the file as New IK chain.pz3.

[Figure 5] Chain break applied to right collar (left). [Figure 6] Mushroom with IK chain (right). 

Use the Chain Break Tool

1. Open Poser with the default figure visible.

2. Select Window, Editing Tools to make the Editing Tools buttons visible, if necessary.

3. Select and pull the right upper arm element away from the center of the figure.

Notice how the torso moves with the arm element.

4. Select the Chain Break Tool from the Editing Tools (or press the L key) and click the left collar element.

A Chain break icon is place in the center of the element, as shown in Figure 5.

5. Select the Translate/Pull tool from the Editing Tools (or press the T key) and drag the left upper arm.

With the chain break icon placed on the left collar element, the torso remains fixed as you move the left upper arm.

6. Select File, Save As and save the file as Chain break figure.pz3.

Create an IK Chain

1. Select File, Open and open the Mushroom groups.pz3.file

2. Select Window, Hierarchy Editor to open the Hierarchy Editor.

3. Scroll to the bottom of the Hierarchy Editor and select the IK Chains title. Then, click the Create IK Chain button at the bottom of the dialog box.

4. In the Set Name dialog box that appears, accept the name New IK Chain, and click OK.

5. Scroll to the list of mushroom bones in the Hierarchy Editor and select and drag the Stem1, Stem2 and Stem 3 elements and drop them on the newly created IK Chain title.

6. Reorder the stem elements so the appear in order with the Stem3 element designated as the goal.

7. Click the square box to the left of the new IK chain title to enable the IK chain. Then, select and move the top element in the Pose Room.

As the top of the mushroom is moved, the stem bones of the IK chain are also moved, as sown in Figure 6.

8. Select File, Save As and save the file as Mushroom with IK chain.pz3.

Find out more about how to put the power of Poser 7 to work as you learn how to use the new Talk Designer to automatically sync facial animations to an audio track, combine the power of Poser 7 with other software packages, create new motions using the new animation layers feature and much more. Check back to VFXWorld frequently to read new excerpts.

Poser 7 Revealed: The e frontier Official Guide by Kelly L. Murdock. Boston, MA: Thomson Course Technology, 2007. 592 pages with illustrations. ISBN 13: 978-1-59863-296-5; ISBN 10: 1-59863-296-5 ($29.99).

Kelly L. Murdock has a background in engineering, specializing in computer graphics. He has worked on several large-scale visualization projects, created 3D models for several blockbuster movies and has worked as a freelance 3D artist and designer. Murdock is the author or co-author of several books, including seven editions of the 3ds Max Bible, two editions of the Illustrator Bible, Adobe Creative Suite Bible, Maya 7 Revealed, LightWave 3D 8 Revealed and Poser 6 Revealed. He works with his brother at his co-founded design company, Logical Paradox Design.

randomness