© Purushothaman Raju 2019
P. RajuCharacter Rigging and Advanced Animation https://doi.org/10.1007/978-1-4842-5037-2_6

6. CAT Rigging

Purushothaman Raju1 
(1)
Bangalore, Karnataka, India
 

In the previous chapters, we learned how to create a character rig using bones and bipeds. In this chapter, we look at using the improved animation toolkit known as CAT (the Character Animation Toolkit). We look at the tools and options available to aid in rigging a character. As in the chapter on bipeds, a preset character model will be provided along as 3ds Max scenes in the contents folder. Feel free to use any custom 3D model you have or download one and follow along. You can use Autodesk character generator to generate a character or use any other software that generates human characters. This chapter focuses on teaching you how to create and customize a CAT rig, and you will also learn to use the tools and options available for a CAT rig.

Understanding CAT Rig

The CAT toolkit allows you to create a comprehensive rigging system. The variations of rigs you can create are limited only by your creativity. You can have any number of heads, limbs, and tails for your characters. This is where it excels over the biped method. It is always good to understand how both function so you can choose the right tool for the job. Unlike with bipeds, you can create a CAT rig from scratch and build it as you need. However, let’s first see how you can invoke the CAT rigging tool and look at the available presets.

Creating Your First CAT Rig

Fire up 3ds Max if you haven’t already done so and go to the Create panel. Then go to the Helpers panel. In the Helpers menu, choose CAT Objects (see Figure 6-1).
../images/477189_1_En_6_Chapter/477189_1_En_6_Fig1_HTML.jpg
Figure 6-1

Choose CAT Objects from the Helpers menu

Once you choose CAT Objects, click on CATParent from the Object Type options (see Figure 6-2).
../images/477189_1_En_6_Chapter/477189_1_En_6_Fig2_HTML.jpg
Figure 6-2

CAT object types

Once you choose CATParent, you will see a huge list of presets like alien, spider, angel, and so on (see Figure 6-3). For now, you can choose one to your liking and then click and drag it into the viewport.

The presets include a familiar looking biped named Bip01. Try these out to see what rig presets are available.
../images/477189_1_En_6_Chapter/477189_1_En_6_Fig3_HTML.jpg
Figure 6-3

CAT rig presets

Alternatively, you can load the CAT_Rig_presets.max file. This file has all the CAT rig presets created in a single file for reference (see Figure 6-4).
../images/477189_1_En_6_Chapter/477189_1_En_6_Fig4_HTML.jpg
Figure 6-4

CAT rig variations

You can use these rigs as a starting point if it suits the anatomy of your model. Reset 3ds Max for a fresh file and create a CAT rig type of Base Human.

Now with the Base Human CAT rig created, go into the Modify rollout from the control panel on the right side and select the triangle that you see in the bottom of the rig. This triangle is a helper object that will allow you to reposition and reorient the rig as needed.

With the base triangle selected, in the modify options, you will be able to name your character and adjust its size using the CAT Unit Ratio.

Creating a CAT Rig from Scratch

In this section, we are going to create a custom rig.
  1. 1.

    Fire up 3ds Max.

     
  2. 2.

    Load Human_Start.max from the source folder. You should see a human character. I created this character using makehuman; you can use another model that you have to follow along.

     
  3. 3.

    We are going to create a rig for this character and not use the available presets.

     
  4. 4.

    Since the character is going to be a reference for us at this point, select the character model and press ALT+X to turn on Xray mode. Then right-click on the model and freeze it. This way you will be able to see the model but not select or move it. (See the Human_Start_1.max file.)

     
  5. 5.

    Go to the command panel and choose Create ➤ Helpers ➤ CAT Object.

     
  6. 6.

    Choose CATParent and ensure that None is selected in the preset. (We want to create a rig from scratch.)

     
  7. 7.
    Now click and drag in the viewport and you should notice that only the triangle helper is created. (Let’s reference this part as rig_controller going forward instead of calling it a blue triangle.) When you are happy with the size, right-click to complete creation mode. (If you are using a custom model that you downloaded or created using other apps, ensure that the triangle and character are facing the same direction.) See Figure 6-5.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig5_HTML.jpg
    Figure 6-5

    Rig_Controller facing the direction of the model

     
  8. 8.

    Go to Modify ➤ CATRig Parameters and give it a name. I call it CustomRig.

     
  9. 9.

    Reposition your CustomRig (the triangle helper) to 0, 0, and 0. You can select any object and, with the Move tool selected, press F12 to get the Move Transform dialog. In the Absolute world, type in 0, 0, 0. Alternatively, you can use the X Y Z input below the time slider to input the values.

     
  10. 10.
    Now with the CustomRig selected, click on Create Pelvis, as shown in Figure 6-6.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig6_HTML.jpg
    Figure 6-6

    CAT rig, Create Pelvis option

     
  11. 11.
    A new object called hub001 is created. Rename it pelvis by selecting it and going to the Modify tab to rename it. You can use the input parameters to tweak it or use the transform tools. See Figure 6-7.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig7_HTML.jpg
    Figure 6-7

    CAT rig, Pelvis

     
  12. 12.

    Now select the newly created pelvis and position it at the pelvis area of the 3D model. Feel free to reposition, reorient, and scale the pelvis mesh that was created to better suit the character’s model.

     
  13. 13.

    Now with the pelvis selected, click on the Add Leg button, and you will have a leg created with ankle and feet. Again reorient the parts of the leg to match the geometry in all views. (In cases where your model is a dog, tiger, or any other quadruped, you can select the thigh bone and choose how many joints it has.) Refinement and absolute positioning is more important here, because the better the parts are aligned and oriented to the model, the easier the process of skinning will be. Also it is good practice to scale your bones to match the overlapping mesh for skinning purposes. This can be done later as well.

     
  14. 14.

    Select your character rig pelvis again and add a leg. It adds the leg with the transformations and rotations and scales on the other side automatically.

     
  15. 15.

    At any point, if you make a mistake, you can select a root bone and delete all its children bones.

     
  16. 16.
    If your foot bone requires toes, select the feet and change the number in Num Digits. For this exercise, we don’t need toe bones, as our character is wearing shoes (see Figure 6-8).
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig8_HTML.jpg
    Figure 6-8

    CAT rig toe setup

     
  17. 17.

    Let’s move on to the spine area. Select the pelvis and add a spine.

     
  18. 18.
    Select the topmost part of the spine that is created and move and position it. The spines are not always straight up, so rotate and reposition them as needed. See Figure 6-9.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig9_HTML.jpg
    Figure 6-9

    CAT rig, spine setup

     
  19. 19.

    With the top of the spine selected, go into Modify and click on Add Arm. Once the arm has been added, reposition, reorient, and scale it as needed, so that the arm fits inside the model perfectly.

    Note If you double-click on any part of a rig, you can automatically select all the child rig parts associated with it.

     
  20. 20.

    If you need fingers, select the palm of the character and choose the number of digits (similar to leg toes). Ensure that you position the fingers in the right position.

     
  21. 21.

    Once you have positioned the parts of the arm correctly, choose the top part of the spine and click Add Arm. This should mirror it exactly. (See the Human_Start_3.max file.)

     
  22. 22.

    Now select the top part of the spine and rename it Torso.

     
  23. 23.

    Select the torso and choose Add Spine (this will serve as the rig’s neck and head).

     
  24. 24.
    Select the start of the spine and choose the number of segments you want for the neck spine. Ideally, you should have one for the neck and one for head. In this exercise, I used three: two for the neck and one as the connector for the head and neck. See Figure 6-10.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig10_HTML.jpg
    Figure 6-10

    CAT rig, neck and head setup

     
  25. 25.

    Tweak the rig parts to cover the mesh as much as possible. This helps during the skinning process.

     

We have created a human rig entirely from scratch using rig parts. At this point, I recommend you reset 3ds Max and load the preset rigs and then analyze each part to understand how it’s used to create an entirely different type of rig. There are cases where you need extra rig parts, so feel free to select a part and click Add Bone. (Reposition and reorient as needed.)

Saving and Loading a CAT Rig

Load 3ds Max and open the Human_Start_4.max file. In this section, let’s look at saving the custom rig that we created for future use.
  1. 1.

    Open Human_Start_4.max.

     
  2. 2.

    Select the rig_controller (the triangle at the bottom).

     
  3. 3.
    Go into the modify options in the control panel and choose the Save icon. You can save the rig in .rg3 format. See Figure 6-11.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig11_HTML.jpg
    Figure 6-11

    Saving a CAT rig

     
  4. 4.

    Your rig is saved for future use. You don’t need to recreate it all over again.

     
Let’s look at how we load a rig.
  1. 1.

    Reset 3ds Max.

     
  2. 2.

    Create a CAT parent with None as the type.

     
  3. 3.

    Select the triangle root of the rig.

     
  4. 4.

    In the modify options, click on Load and choose the rig. (The icon next to the Save Rig option.)

     
  5. 5.

    A rig named human_ch6.rg3 is provided in the rig folder.

     

CAT Rig Layers

Create a new scene in 3ds Max and create a Base Human rig. Customize it to your liking. Once you’re done, go into the motion panel.
../images/477189_1_En_6_Chapter/477189_1_En_6_Fig12_HTML.jpg
Figure 6-12

CAT rig Layer Manager

Note in Figure 6-12 the red icon in the Layer Manager. This is the default for all rigs, which means that you are in setup mode and the rig is being prepped. To begin animating this rig, we need an animation layer to be active.
../images/477189_1_En_6_Chapter/477189_1_En_6_Fig13_HTML.jpg
Figure 6-13

CAT rig layer types

When you click on the fly-out of layers, as shown in Figure 6-13, you will see four layers types. They are discussed next.

Absolute Layer

The Absolute layer is the basic animation layer used for keyframe animation. Note that this layer will override any other layers below it.
  1. 1.
    Clicking on this option creates an absolute layer. Once the absolute layer is created, you can click on the red icon, the setup icon, and toggle it to animation mode. Animation mode is indicated by a green play icon. See Figure 6-14.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig14_HTML.jpg
    Figure 6-14

    CAT rig, animation/setup mode

     
  2. 2.

    Now select the pelvis and turn on auto key.

     
  3. 3.

    Move to frame 25 and bring the pelvis down in the Y axis. Move to frame 50 and move it up at 75, down again, and up at 100 (similar to a squat animation).

     
  4. 4.
    Now click on the Absolute layer once more and add another layer. To avoid confusion, let’s name the layers SquatAnimation and HeadAnimation, respectively, in order of creation. See Figure 6-15.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig15_HTML.jpg
    Figure 6-15

    CAT rig, layer rename

     
  5. 5.

    Now choose the newly created layer called HeadAnimation and, with auto key on, make it look left and right or up and down, based on your preference.

     
  6. 6.

    If you play this back, you’ll notice only one animation is playing. In the Global Weight, choose 50%. Now you should be able to see a blend of animation between the layers. Note that these values can be animated. You can animate the parts in individual layers or in one layer. By animating them as individual layers you have control over how one layer blends with the other.

     
  7. 7.

    A point to remember is that when there is more than one absolute layer, the top layer will play the animation and the other layers can be blended with the global and local weights.

     

Local and World Layers

The local layer is often known as the adjustment layer. Reset 3ds Max and create a new CAT rig. For this purpose, let’s use the Human rig we created in an earlier section.
  1. 1.

    Alternatively, load CAT_AdjustmentLayer.max.

     
  2. 2.

    Select the triangle base and go into the motion options.

     
  3. 3.

    Go to the Clip Manager rollout and choose Browse for Motion Capture Files. We are going to use the bip motions that we created in the bipeds chapter. CAT rigs support them.

     
  4. 4.

    Go to the Tools menu and choose Measure Distance. You need to find the height of your CAT rig. Click on the top of the head and the bottom of the feet. Your status bar should show the distance.

     
  5. 5.
    Browse to the the bip motions in your source folder and load Jump_Animation.bip (If you can’t see the file, ensure that the file type is set to bip in the Open dialog box.) I use Jump_Animation.bip for this exercise. See Figure 6-16.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig16_HTML.jpg
    Figure 6-16

    CAT rig, import a bip

     
  6. 6.

    Input your height. In my case, it was 180, so I input that value in the Biped Height and click OK.

     
  7. 7.
    Your biped will be imported and your CAT rig will follow the biped motion, as shown in Figure 6-17.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig17_HTML.jpg
    Figure 6-17

    CAT rig imported animation

     
  8. 8.
    Click on Capture Animation. This will bake the animation to the CAT rig. You might get a popup like the one shown in Figure 6-18.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig18_HTML.jpg
    Figure 6-18

    Capture Animation Cleanup dialog

     
  9. 9.

    Click Yes. This is going to remove the bip and its supporting layers after baking the animation to the CAT rig.

     
  10. 10.

    Load the reference file called CAT_AdjustmentLayer1.max.

     
  11. 11.

    Scrub. You won’t see the biped anymore, but your CAT rig still has the animation.

     
  12. 12.

    Select any part of the rig and go into the motion panel. Select the animation layer. You should see that many keyframes are created when you captured the animation from your biped.

     
  13. 13.

    In the motion panel, add a World adjustment layer. It has a layer icon of [+W] in the Layer Manager.

    Note Adding a World adjustment layer does not affect the animation like with a Local adjustment layer.

     
  14. 14.

    With the adjustment layer selected, you can overlay tweaks to your motion that were already keyed and the rig will compensate too.

    In the reference file called CAT Adjustmentlayer2.max, I spread the legs apart and the hands rotate in the adjustment layer. See how it seamlessly fits along in the animation. Playing with the adjustment layer Global Weight is interesting as well. We can observe the adjustment of the weight in action.

     

CAT Motion Layer

Let’s look at the last layer type—the CAT motion layer. Reset 3ds Max and create a CAT rig. Let’s use Base Human for this exercise.

  1. 1.

    Create a CAT rig with the Base Human type.

     
  2. 2.

    Select the root triangle and go to the motion options.

     
  3. 3.

    In the layer type, create a CAT Motion layer (it’s the last layer type in the layer manager and is denoted by a running icon). Enable Animation mode by clicking on the Setup/Animation mode toggle button.

     
  4. 4.

    If you play the animation, you will see the CAT rig is doing a walk animation.

     
  5. 5.
    In order to tweak the animation, click on the motion editor icon, as shown in Figure 6-19.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig19_HTML.jpg
    Figure 6-19

    CAT motion editor icon

    The CAT motion editor allows us to tweak the walk in an organized way. See Figure 6-20.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig20_HTML.jpg
    Figure 6-20

    The CAT motion editor

     
  6. 6.

    In the CAT motion popup window, the left panel lists the structure of your CAT rig.

     
  7. 7.
    Let’s select the head and expand the HeadGroup, as shown in Figure 6-21. The head has all these animations.
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig21_HTML.jpg
    Figure 6-21

    CAT motion, head twist curve

     
  8. 8.

    Select the twist and check out the graph on the right. CAT provides the functionality to edit during playback.

     
  9. 9.

    Play the animation and change the scale of head twist from 100 to 25, or increase it to extremes to see the preview.

     
  10. 10.

    This is a powerful tool and there are no precise values. It varies based on the rig and type of animation you want. Play around and tweak as needed until you are happy with the results.

     
  11. 11.

    Note that the CAT_Rig is walking in place; this is often called in-place animation.

     
  12. 12.
    In order to have the CAT rig move in the 3D space as it walks, you must go to Globals in the left pane of the CAT motion editor (see Figure 6-22).
    ../images/477189_1_En_6_Chapter/477189_1_En_6_Fig22_HTML.jpg
    Figure 6-22

    CAT motion, Globals

     

  • Start and End determine when the walk begins and ends.

  • The Max Step Time, when set to a lower value, makes the character move faster.

  • Max Stride Length determines the distance between each step. The higher the number the longer the step.

  • Walk In Line allows the character to move forward as it walks.

  • Walk on Path enables the path node and allows you to select a path.

  • The walk direction is determined by these settings:

    • 0 means the character moves forward

    • 90 means the character strafes to the left

    • -90 means the character strafes to the right (Think of it as a circle of 360 degrees, so 0 is forward and so on… If you input a 45, you will notice the character move diagonally.)

  • A gradient of 0 means the character moves parallel to the ground. A positive value will make it climb up a hill and a negative value will make it climb down a slope.

This is a powerful tool and is very useful when used creatively. You can combine this animation with a World adjustment layer to get variations; the possibilities are limitless.

CAT Rig: Motion Path

In this section, we set up our CAT rig to follow a path.
  1. 1.

    Fire up 3ds Max and create a Base Human CAT rig.

     
  2. 2.

    From the Create panel, create a path using the Line tool in the top viewport.

     
  3. 3.

    Let’s also create a helper to aid us. Create a standard dummy from the Helper section.

     
  4. 4.

    Position the newly created dummy at the beginning of path. With the dummy selected, go to Constraints and choose the Path constraint. Then choose the path.

     
  5. 5.

    Select the Rig_Controller of the CAT rig (the triangle at the base of the CAT rig) and go to the motion options.

     
  6. 6.

    Create a CAT motion layer and open the CAT motion editor. Ensure that you have animation mode in the Setup/Animation mode of the layer manager in order to see the preview of the animation as you tweak its values.

     
  7. 7.

    Enable Follow mode in the motion options panel of the dummy so that the dummy orients itself toward the path.

     
  8. 8.

    Now go to your CAT motion editor and, in the Globals, choose Walk On Path Node and choose the dummy helper.

     
  9. 9.

    You might notice that the character is in the wrong axis now, but it walks on the path. A simple fix would be to reorient the dummy in Local mode (Local mode can be chosen from the ribbon toolbar). The CAT rig will reorient itself. You might need to animate the dummy’s orientation so that the CAT rig faces the direction it is walking.

     
  10. 10.

    Tweaking the path will force the CAT rig to follow the dummy, which is constrained to the path.

     
  11. 11.

    The reference file called CAT_Motionpath_Complete.max is available for your reference.

     

Summary

In this chapter, we learned about the different types of CAT rigs that are available. We also learned how to create a CAT rig entirely from scratch, as well as about the various animation layer types and how they can aid us in blending multiple animations. We took the CAT rigs a step further by looking at how at how we can load motion clips created from bipeds into CAT rigs and create procedural animation using the CAT motion editor. In the next chapter, we will look at binding our mesh to the rigs we created. This process is called skinning.

..................Content has been hidden....................

You can't read the all page of ebook, please click here login for view all page.
Reset
3.144.93.73