Rigging Characters for Animation, Pt. 1, From New Riders | 6 | WebReference

Rigging Characters for Animation, Pt. 1, From New Riders | 6

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Inside Maya: Rigging Characters for Animation. Pt. 1.

IK Spline Tail and Ears Setup

The technique used for the IK spline tail and ears setup is a very common combination of IK splines, with some added FK-style control. The technique you will use in the next exercise is basically to create a spline IK for the entire hierarchy of joints and then draw a low-res joint hierarchy right on top of where the IK spline curve was created (usually two to three joints is enough). Next, you'll simply smooth-bind the low-res joints to the IK spline curve. This is a nice way to get some FK feeling control and still have the ability to translate the joints for IK spline-style results.

Exercise 17.2 Character Setup for Spot's Tail and Ears

This exercise again is performed only on the tail. The exact same technique should then be used on the ears as well.

  1. Start with the completed file from the last exercise, Dog_LegsSetup_Finished.mb, which you can find on the accompanying CD.

  2. Go to the IK Spline tool by clicking the menu item Skeleton, IK Spline Handle Tool, Options Box. Hit the Reset Tool button at the bottom, and then be sure to uncheck the Auto Simplify Curve and Auto Parent Curve options.

  3. Draw an IK Spline curve from the root of the hierarchy, all the way to the last joint in the hierarchy. In this case, it is a nine-joint tail; you create the spline handle starting from the Dog_tail_1 joint and ending at the Dog_tail_9 joint.

  4. Next, using the Joint tool and holding down the c key to enter Curve Snap mode, draw a low-res four-joint hierarchy directly on top of the spline curve that was just autocreated by the IK spline tool.

  5. Translate the new hierarchy upward just enough that it is not right on top of the other joint hierarchy, and rename each joint in the hierarchy TailControlJoint (see Figure 17.12).

    Figure 17.12
    Creating a low-res control hierarchy.

  6. Next, select the highest parent of the TailControlJoint hierarchy and Shift+select the NURBS curve that was created automatically by the IK spline tool. You might have to use the Hypergraph to select this curve because the joints are in the way.

  7. With the current selection, click Skin, Bind Skin, Smooth Bind using the default options.

  8. Select the root of the new low-res control hierarchy and parent it to the node that you want to rotate the real tail hierarchy that has the IK spline solver attached to it. In this case, I parented the new TailControlJoint hierarchy to the Dog_HipsJoint node so that when you rotate the hips, the tail wags along with them.

  9. Perform these steps for both the ears. The steps are exactly the same.

  10. When you are finished, group any ungrouped spline IK handles as well as spline IK curves under a new group node. Then put this group node somewhere in the character's hierarchy that will not have animation applied to it. In this case, I added a new group node to DogMainTransform and called it Dog_character. This group parents anything related to the character that should not be animated as a child of it.

  11. Be sure to lock the translates, rotates, and scales of the Dog_character group node. Parent all the leftover IK controls and NURBS curves under the Dog_character group node.

    You can find the completed setup in the file Dog_TailAndEarSetup_Finished.mb on the accompanying CD.

Low-Res Stand-In Geometry

As the following exercise shows, creating stand-in geometry is a very simple process. This geometry is simply a low-resolution version of the actual character geometry, which is then cut up into a separate piece per joint using a combination of the Cut Poly Faces tool and the Poly Separate command. The cut polygon pieces are then simply made a child of the joint that they correspond to. Now, the low-res geometry moves with the joint hierarchy but is not bound or deforming, so it is extremely fast and interactive for the animator to use.

Exercise 17.3 Creating Low-Res Stand-In Geometry

For this exercise, you begin with the finished file from the previous exercise, Dog_TailAndEarSetup_Finished.mb, which you can find on the accompanying CD.

  1. Import into the Dog_TailAndEarSetup_Finished.mb file the low-res dog file, called Dog_lowResPolyStandIn.mb, which you'll find on the accompanying CD (see Figure 17.13).

    Figure 17.13
    A low-res version of the character model is used for the low-res stand-in geometry.

  2. Take a look at the joint hierarchy of the dog, and start to figure out where you want to cut your low-res poly object into separate pieces. A general rule is that you will need to cut your character in any place that it will need to bend, or any child that will need to rotate independently from its parent to achieve the articulation of the character's pose.

  3. Select the low-res polygon character. Activate the Cut Poly Faces tool by clicking Edit Polygons, Cut Faces Tool (it might say just Cut Faces, depending on your tool settings) Option Box (see Figure 17.14).

    Figure 17.14
    Select the low-res polygon character, and activate the Cut Poly Faces tool.

  4. Now, with the options from the previous figure, drag your mouse across the geometry and watch as the Cut Faces tool creates a straight line across your geometry. This is where the polygons will be cut when you release the tool. Cut the polygons. Experiment with where you are cutting the geometry and how well it lines up with the location of the joint.

  5. Next, after you have cut the polygon, perform the menu commands Edit Polygons, Separate and then Edit, Delete by Type, History.

  6. Cut the geometry into a separate piece for each joint, trying not to cut across other parts of the geometry that shouldn't be split yet. Then, each time you cut, separate the polygons and delete the history. Eventually, you will be finished cutting up the entire geometry.

  7. Next, one by one, select each polygon piece that you cut, and Shift+select the closest joint that you cut that piece for. Hit the p key on your keyboard to parent the geometry to the joint. Do this for each separate piece that you cut for the character.

    You can find the finished file with the low-resolution stand-in character properly cut and parented in the file Dog_LowResStandIn_Finished.mb on the accompanying CD.

Created: March 27 2003
Revised: November 7, 2003

URL: http://webreference.com/3d/insidemaya/1