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Constraints & Motion Capture

Maya Constraints

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Page 1: Maya Constraints

Constraints &

Motion Capture

Page 2: Maya Constraints
Page 3: Maya Constraints

Using Maya: Dynamics 3

Constraints & Motion Capture23 Basic Constraints 5

Understanding basic constraints 5

Objects and targets 6

Why use constraints? 6

Working with constraints 7

Creating or adding targets to a constraint 7

Removing constraint targets 8

Adjusting the target weights 8

Constraining an object’s position 11

Constraining an object to a point 11

Constraining an object to a surface 12

Constraining a pole vector of an IK handle 13

Constraining an object’s orientation 14

Matching an object’s orientation to another object 14

Constraining an object’s aim 15

Constraining an object to the normal of a surface 16

Constraining an object to a tangent 17

Controlling “up” 18

Constraining an object’s scale 19

Constraining an object’s scaling values 19

24 Motion Capture 21Getting started with motion capture 21

Basic procedure for simple motion capture 21

Terminology 22

Using the Device Editor 23

Learning about motion capture 24

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DynamicsContents

Defining motion capture devices 25

Listing devices and attachments 26

Attaching attributes and commands 27

Attaching attributes 27

Attaching commands 28

Modifying existing attachments 29

Mapping device data 30

Saving attachments 31

Capturing motion 33

Rehearsing the motion 33

Recording the motion 33

Reviewing the motion 34

Saving files to disk 36

Using filters and resamplers 39

Reviewing takes 40

Using multiple devices 41

Performing full-body motion capture 42

Tips for full-body motion capture 42

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23 Basic Constraints

Using basic constraints, you can control the position, orientation, or scale ofone object based on the position, orientation, or scale of one or more “target”objects. In addition, you can impose specific limits on objects and automateanimation processes.

For example, if you want to quickly animate a sled sliding down a bumpyhill, you might first use a Geometry Constraint to constrain the sled to thesurface. You could then use a Normal Constraint to make the sled sit flat onthe surface. After you create these constraints, you key the sled’s positions atthe top and bottom of the hill. The animation is then complete.

This chapter describes how to use these constraints, including:

• “Understanding basic constraints” on page 5

• “Working with constraints” on page 7

• “Constraining an object’s position” on page 11

• “Constraining an object’s orientation” on page 14

• “Constraining an object’s scale” on page 19

Understanding basic constraintsYou can constrain an object’s position, orientation, or scale to a target(s).There are eight basic constraints:

Position

• Point Constraint

• Geometry Constraint

• Pole Vector Constraint

Orientation

• Orient Constraint

• Aim Constraint

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Basic ConstraintsUnderstanding basic constraints

• Normal Constraint

• Tangent Constraint

Scale

• Scale Constraint

Objects and targetsWhen describing constraints, we use the terms object and target, where:

• Object is the name of the transform you constrain.

• Target is the name of the DAG node(s) to which the object is constrained.

Why use constraints?If two objects share a common DAG parent, you can use an expression or aconnection to copy a set of translation, rotation, or scale values from oneobject to another. However, if the two objects have different parenttransforms, this procedure may produce wildly different motions, as in thefollowing example.

Example: Why constraints are useful

1 Create three objects: a sphere named s and two cones named c1 and c2.

2 Parent c1 to s.

3 Connect the translation value of c2.t to c1.t.

4 Select c2 and drag it using the Move Tool.

The two cones should appear as one.

5 Rotate s by 90 degrees (on any axis).

6 Select c2 and drag it using the Move Tool.

Notice that the two cones are no longer coincident.

Tip

When working with constraints, always select the object last. In otherwords, to add, change, or remove targets, select the target, then select theconstrained object.

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Since c1 and c2 are no longer parented to the same transform, this simplescheme cannot work. However, by placing a Point Constraint on c1 andselecting c2 as the target, you could then move c2 and c1 would followregardless of the objects’ parent transforms.

Working with constraintsYou create all constraints in the same way, whether you are using them tocontrol position, orientation, or scale.

The constraint work flow consists of these basic tasks:

• Creating or adding targets to a constraint

• Removing constraint targets

• Adjusting the target weights

Creating or adding targets to a constraintTo create a constraint or add targets to an existing constraint, you first selectthe targets, then the constrained object, and finally the constraint type.

To create or add targets to a constraint:

1 Select the target object or objects (shift-click to select more than one target).

2 Select the object you want to constrain.

3 Select Animation→Constraint to select the constraint type.

After you select a constraint type, the constrained object moves to its newconstrained position or orientation. If multiple targets are used, theircombined effect, in general, is the weighted average of each of theirindividual effects.

If the specified constraint type does not already exist for the selected object,Maya creates one. If the object already has a constraint of the type specified,Maya adds the targets to it and applies the current option box settings.

Tip

If you cannot add a constraint by selecting the constraint type, check theoption box (❐) for that constraint to be sure the Add Targets option isselected.

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Basic ConstraintsWorking with constraints

The Reset button sets the constraint operation to Add targets. However,since all option box settings are applied each time you add a target, youprobably don’t want to select this unless you are creating a new constraint.

Removing constraint targetsOnce added, a constraint target influences the constrained object. You canend this influence by removing the target from the constraint.

To remove targets from a constraint:

1 Select the first constraint target you want to remove.

2 Shift-click to select any additional targets you want to remove.

3 Select the constrained object.

4 Use the Constraint pull-down menu to open the option box (❐) for theconstraint type you want to remove targets from.

5 Select Remove Targets in the option box.

6 Click Add/Remove at the bottom of the option box.

7 Reset the option box by selecting Add Targets.

8 Click the Close button.

The constrained object updates its position to reflect the target removal(s).When you remove the last constraint target, you also remove the constraint.

Adjusting the target weightsFor a constraint with multiple targets, you can control the influence ofindividual targets by adjusting their target weights.

To set a target weight using the Channel Box:

1 Select the constrained object.

The constraint is listed in the Shapes section of the Channel Box. The targetweights are listed next to the target names, as shown in the following figure.

Note

When you remove a target, it also removes any animation curves attachedto the constraint for that target.

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2 Enter values for the target weights.

You can also set keys by clicking on a Target Weight box with the rightmouse button.

To set a target weight using the Attribute Editor:

1 Select the constrained object.

2 Open the Attribute Editor, Window→Attribute Editor.

3 Select the tab for the constraint.

4 Open the Extra Attributes section. The target weights are listed next to thetarget name, as shown in the following figure.

The constraint is listed here.

The target weights are listed here.

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Basic ConstraintsWorking with constraints

The target weightsare listed here.

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5 Enter values for the target weights. You can also set keys by clicking on aTarget Weight box with the right mouse button.

Constraining an object’s positionThis section describes the various ways you can constrain an object’sposition, including:

• Constraining an object to a point—the Point Constraint

• Constraining an object to a surface—the Geometry Constraint

• Constraining a pole vector of an IK handle—the Pole Vector Constraint

Constraining an object to a pointA Point Constraint causes an object to move to and follow the position of atarget object or to the average position of several target objects. Thisconstraint is useful for having one object match the motion of anotherwithout regard for its parent transform or orientation. You can also use thisconstraint to animate one object to follow a series of targets by animating theconstraint weight.

The object’s orientation is not affected.

To constrain an object’s position based on the target’s position:

1 Select the target object or objects. (Shift-click to select more than one target.)

2 Select the object you want to constrain.

3 From the Animation menu bar or Hotbox, select Constraint→Point.

Note

Setting all target weights to 0 does not remove the constraint, but causes itto “freeze” the object.

Tip

You can often get useful results using expressions to drive multiple targetweights based on the value of a single dynamic attribute. For example, youcould constrain an object to move from target to target by setting oneweight to a value on the range (0 to 1) and setting the other to 1 minus thatvalue.

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Basic ConstraintsConstraining an object’s position

If you select only one object as the target, the rotate pivot point of theconstrained object moves to the rotate pivot point of the target. If you selectseveral target objects, the constrained object moves to the average of thetarget objects’ pivots (see “Adjusting the target weights” on page 8).

Once you constrain an object, moving the target object also moves theconstrained object in the same way.

Constraining an object to a surfaceThe Geometry Constraint restricts a constrained object to a surface, curve, ormesh. Specifically, the object’s rotate pivot point is constrained to the targetsurface. Geometry Constraint targets can be NURBS surfaces, NURBScurves, or polygon surfaces. It is similar to creating a motion path for anobject, except that the object can move freely over the surface of the targetgeometry. This constraint is useful for constraining an object’s location to asurface such as a floor or staircase.

The constrained object’s orientation is not affected.

To constrain an object to a surface:

1 Select the target surface, curve, or mesh. (Shift-click to select more than onetarget.)

2 Select the object you want to constrain.

3 From the Animation menu bar or Hotbox, select Constraint→Geometry.

When you move the constrained object, it is constrained to the target surface.If you move the target surface, the constrained object will follow and moveto the point on the target surface closest to the object’s previous position.

Tip

Unlike the Point Constraint, you can set keys for the position of thegeometry-constrained object (or apply a Point Constraint to it also). Theobject’s geometry-constrained position will be the point on the targetsurface, closest to the keyed (or point-constrained) position.

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If you add more than one target, the object is constrained to the targetsurface that has the highest weight. (See “Adjusting the target weights” onpage 8.)

Constraining a pole vector of an IK handleThe Pole Vector constraint applies only to IK handles that use the rotateplane IK solver (see “Creating IK handles” on page 238 of Chapter 12,“Posing and Animating Skeletons”). The effect is similar to the Constrainingan object to a point above, except this constraint controls the location of thePole Vector end-point.

You can use constraints with inverse kinematics to create realistic charactermovements simply. For example, say you want to animate an inversekinematic character riding a bicycle. You can key the rotation of pedals onthe bicycle, then constrain the effector of the character’s leg skeleton to thepedal. Now the leg of your character follows the keyed rotation of thepedals, creating the illusion that the character is pedaling the bicycle.

For more information on inverse kinematics, refer to the CharacterAnimation section of this book.

To create (or add targets to) a Pole Vector Constraint:

1 Select the first constraint target.

2 Shift-click to select any additional targets.

3 Select the handle for the pole vector you want to constrain.

4 From the Animation menu bar or Hotbox, select Constraint→Pole Vector.

Notes

If all the targets have the same weight, as happens when you create aGeometry Constraint, the target used is the one with the lowest index. Thetarget index indicates the order in which you selected the targets duringthe constraint creation (the first target selected has the lowest index). Youshould animate the target weights such that only one target has the highestweight at any given frame.

The Geometry Constraint is history dependent. The end result of anobject’s animation depends on where the object started.

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Basic ConstraintsConstraining an object’s orientation

The IK chain rotates so that the Pole Vector lies at the target pivot. If youadd multiple targets, the Pole Vector is placed at the weighted average of thetarget positions. For example, if you select two targets with the same weight,the IK chain rotates so that the Pole Vector is halfway between them.

Constraining an object’s orientationThis section describes the various ways you can constrain an object’sorientation, including:

• Matching an object’s orientation to another object—the Orient Constraint

• Constraining an object’s aim—the Aim Constraint

• Constraining an object to the normal of a surface—the Normal Constraint

• Constraining an object to a tangent—the Tangent Constraint

Only one of these constraints can be present on a given object, as eachconnects to the x, y, and z rotation attributes of the object. Aim, Normal, andTangent Constraints have the same Aim and Up parameter options.

Matching an object’s orientation to another objectThe Orient Constraint matches the orientation of one object to that of a targetobject(s) without changing the constrained object’s location. This constraintis useful to make several objects orient in sync. For example, you can make agroup of people look in the same direction at the same time by animatingone head and then constraining the orientation of all the others to this head.

If you select several target objects, the constrained object’s orientation is anaverage of their orientations.

To constrain the orientation of one object to another:

1 Select a target object or objects. (Shift-click to select more than one target.)

2 Select the object you want to constrain.

3 From the Animation menu bar or Hotbox, select Constraint→Orient.

Tip

Remember, you can produce useful results by combining multiple targetweights with an expression.

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If you have only one target object, the constrained object changes to thetarget’s orientation. If you have several targets, the constrained objectchanges to the targets’ average orientation (see “Adjusting the targetweights” on page 8).

When you rotate the target object(s), the constrained object also rotates.

Constraining an object’s aim

The Aim Constraint aligns the aim vector of one object to follow themovement of a target object or objects. The Aim Constraint is useful forlights and cameras; you can aim a light at an object or a group of objects, forexample, to follow their animation.

To create (or add targets to) an Aim Constraint:

1 Select a target object or objects. (Shift-click to select more than one target.)

2 Select the object you want to constrain.

3 From the Animation menu bar or Hotbox, select Constraint→Aim→❐ todisplay the Aim Options window.

4 Click Add/Remove.

When you move the target object, the aim vector of the constrained object(the X-axis is the default) repositions itself to aim at the target.

5 Change the vectors if you want to aim the selected axis of the constrainedobject.

You can aim the constrained object by changing one of these vectors:

Aim Vector Sets the aim vector—the vector in local coordinates thatorients to the target. The default is the X-axis: 1.0, 0.0, 0.0.

Up Vector Sets the local up vector—the vector in local coordinates thataligns with the world up vector. You can use the Up Vectoroption to control the roll of the constrained object as itmoves across the up axis. The default is Y-up: 0.0, 1.0, 0.0.

Note

The effect of multiple targets for orient constraints can be non-intuitive andis not recommended for targets that differ greatly in orientation.

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Basic ConstraintsConstraining an object’s orientation

World Up Vector Sets the world up vector—the vector in world coordinatesthat the local up vector should align with. The default is y-up: 0.0, 1.0, 0.0.

6 Click Close.

Constraining an object to the normal of a surfaceThe Normal Constraint limits the orientation of an object to the normal ofthe constraining surface or mesh on which it travels. This constraint is usefulfor keeping an object perpendicular to a surface, usually when the surface isdeformed, such as a ship sailing over a section of choppy water.

To constrain an object’s orientation to the normal of the surface:

1 Select the target surface or mesh.

2 Select the object you want to constrain.

3 From the Animation menu bar or Hotbox, select Constraint→Normal→❐ todisplay the Normal Options window.

4 Click Add/Remove.

As you move the constrained object along the surface, the aim vectorreorients itself to the normal of the surface.

5 Change the vectors if you want to aim the selected axes of the constrainedobject.

You can align the axes of the constrained object to the normal using thefollowing options:

Aim Vector Sets the aim vector—the vector in local coordinates thatorients to the normal. The default is the X-axis: 1.0, 0.0, 0.0.

Up Vector Sets the local up vector—the vector in local coordinates thataligns with the world up vector. You can use the Up Vectoroption to control the roll of the constrained object as itmoves across the up axis. The default is Y-up: 0.0, 1.0, 0.0.

World Up Vector Sets the world up vector—the vector in world coordinatesthat the local up vector should align with. The default is Y-up: 0.0, 1.0, 0.0.

6 Click Close.

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Constraining an object to a tangentThe Tangent Constraint limits the orientation of an object to the tangent ofthe constraining curve (path) on which it travels. This constraint is useful forhaving an object follow a path’s direction, such as a roller coaster carfollowing the tracks.

To constrain an object’s orientation to the tangent of a curve:

1 Select the target curve.

2 Select the object you want to constrain.

3 From the Animation menu bar or Hotbox, select Constraint→Tangent→❐.

4 Click Add/Remove.

As you move the constrained object along the surface, the aim vectorreorients itself to the tangent of the curve’s surface.

5 Change the vectors if you want to aim the selected axes of the constrainedobject.

You can align the axes of the constrained object to the tangent using thefollowing options:

Aim Vector Sets the aim vector—the vector in local coordinates thatorients to the tangent. The default is the X-axis: 1.0, 0.0, 0.0.

Up Vector Set the local up vector—the vector in local coordinates thataligns with the world up vector. You can use the Up Vectoroption to control the roll of the constrained object as itmoves across the up axis. The default is Y-up: 0.0, 1.0, 0.0.

World Up Vector Sets the world up vector—the vector in world coordinatesthat the local up vector should align with. The default is Y-up: 0.0, 1.0, 0.0.

6 Click Close.

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Basic ConstraintsConstraining an object’s orientation

Controlling “up”Depending on the type of scene you are creating, you may want morecontrol of the object’s orientation. For example, if you were animating aroller-coaster car along a curved and looped track, it would be useful tocontrol the car’s Y-axis orientation (Up Vector) along each keyframe. Thereare several attributes that control an object’s orientation, including:

• Aim Vector

• Up Vector

• World Up Type

• World Up Vector

• World Up Object

The Aim Vector, Up Vector, World Up Vector, and World Up Typeattributes behave identically for the Aim, Tangent, and Normal Constraints.

Aim VectorThis vector in local coordinates of the constrained object points at the target(for Aim Constraint), aligns with the normal (for Normal Constraint) or thecurve tangent (for Tangent Constraint). The default value is (1.0, 0.0, 0.0).

Up VectorThis is the vector in local coordinates of the constrained object that is alignedbased on the World Up Type. The default value is (0.0, 1.0, 0.0).

World Up TypeThis parameter (available only through the command line and AttributeEditor) controls how the Up Vector is aligned. The World Up Type can haveone of five values:

• Scene—the Up Vector is aligned with the up-axis of the scene and the WorldUp Vector and World Up Object attributes are ignored.

• Object—the Up Vector is aimed as closely as possible to the origin of thespace of the World Up Object and the World Up Vector attribute is ignored.

• Object Rotation—the World Up Vector is interpreted as being in thecoordinate space of the World Up Object, transformed into world space, andthe Up Vector is aligned as closely as possible to the result.

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• Vector—the Up Vector is aligned with the World Up Vector as closely aspossible.

• None—no calculation is performed by the constraint, with the resulting UpVector orientation based on the previous orientation of the constrainedobject.

The default World Up Type is “vector”.

World Up VectorThis is the vector in world coordinates (if World Up Type is vector) or in thelocal space of the World Up Object (if World Up Type is object rotation)that the up vector should align with. The default value is (0.0, 1.0, 0.0)

World Up ObjectThe World Up Object is the DAG object used for World Up Type “object”and “objectrotation”. The default value is no up object, which is interpretedas world space.

Constraining an object’s scaleThis section describes how you can constrain an object’s scale.

Constraining an object’s scaling valuesThe Scale Constraint limits the scaling values of an object to the scalingvalues of the target object. This constraint is useful for scaling all objects in ahierarchy at once in accordance to the scaling changes applied to one object.

To constrain an object’s scale:

1 Select the target object.

2 Select the object you want to constrain.

Notes

If you set the World Up Type to None, the Aim, Tangent, and Normalconstraints are history dependent. The end result of an object animationdepends on where the object started.

If you set the Aim and Up Vectors to be collinear, Maya will interpret theWorld Up Type as None.

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Basic ConstraintsConstraining an object’s scale

3 From the Animation menu bar or hotbox, select Constraint→Scale.

When you scale the target object, you will also scale the constrained objectwith the same scaling values.

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24 Motion Capture

With motion capture, you record real physical motion using a motioncapture device. You can use this real-life data to animate characters orobjects in a scene.

Motion capture lets you generate large amounts of complex motion. Youmust plan your motion capture animations meticulously and set them upcarefully.

This chapter describes how to set up and perform motion capture in Maya. Itincludes the following information:

• “Getting started with motion capture” on page 21

• “Defining motion capture devices” on page 25

• “Listing devices and attachments” on page 26

• “Attaching attributes and commands” on page 27

• “Capturing motion” on page 33

• “Using filters and resamplers” on page 39

• “Reviewing takes” on page 40

• “Using multiple devices” on page 41

• “Performing full-body motion capture” on page 42

Getting started with motion captureThis section provides background information on motion capture for thefirst-time user.

Basic procedure for simple motion captureThe workflow for a simple motion capture sequence consists of a few basicsteps.

To create a simple motion capture sequence:

1 Create a target geometry in Maya.

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Motion CaptureGetting started with motion capture

2 Attach the geometry to the motion capture device.

3 Rehearse the motion for the actions that will be performed.

4 Record the motion.

5 Review the recorded motion and insert it into your scene.

It takes a few additional steps to create a full-body motion capture sequence.For details, see “Performing full-body motion capture” on page 42.

TerminologyBefore using motion capture, you should become familiar with a few simpleterms.

Motion capturedevice

To capture motion, you use a motion capture device.

The motion capture device samples motion and records it. With a motioncapture device, you can achieve real-time monitoring and recording of data.

Supported data-server devices in Maya will have servers provided by thedevice vendors. You can write your own servers for custom devices with theMaya Motion Capture Developer’s Tool Kit.

In general, the mouse and keyboard are not motion capture devices.

Server A server is a stand-alone program that communicates with a device. Mayacan talk to the server to get device data. Devices that require servers arecalled data-server devices.

Axis A motion capture device provides information on different axes, arranged ina hierarchy. Axes give important information such as if the data is a rotationvalue, a translation value, or just a number. An axis can be connected (orattached) to an attribute in a Maya scene.

Attachment The connection between a device axis and an object’s attribute is called anattachment. The attachment “tells” the device what attribute in the scene youwant to change.

Button Some motion capture devices have buttons. A button can execute a commandor act as a clutch for an axis. However, button presses cannot be recorded asmotion capture data.

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Using the Device EditorYou use Maya’s Device Editor to control the motion capture process. Todisplay the Device Editor, select Window → AnimationEditors → DeviceEditor.

Device Outliner The top section is the Device Outliner. The Device Outliner lists the defineddevices, the device structures, and what the devices are attached to. Forinformation on how to use the Device Outliner, see “Defining motioncapture devices” on page 25.

Tab sections The lower section provides several tabs that allow you to work with devicesand manage motion capture data.

• The Attachment tab provides settings for making attachments, as describedin “Attaching attributes and commands” on page 27.

Device Outliner

Device Editortabs

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Motion CaptureGetting started with motion capture

• The Mapping tab provides settings for modifying attribute attachments, asdescribed in “Changing the attachment and device mappings” on page 36.

• The Filters tab lets you define filters and resamplers that you can use whenpreviewing motion data or converting it to animation curves. For details, see“Using filters and resamplers” on page 39.

• The Options tab includes miscellaneous options for writing and readingtakes, as described in “Numbering takes” on page 37, “Reviewing takes” onpage 40, and “Using multiple devices” on page 41.

• The Controls tab provides the settings for rehearsing, recording, andreviewing your motion capture sequences. These procedures are describedin “Capturing motion” on page 33.

Learning about motion captureTo help you learn about motion capture, we’ve provided a “toy” motioncapture server, the mayaClockServer program. This simple program reads theSGI system clock and outputs three rotation values, in radians: the angle ofthe second hand, the angle of the minute hand, and the angle of the hourhand. It does not require any special hardware.

The binary is located in the /usr/aw/maya/bin directory and is calledmayaClockServer. To view mayaClockServer options, enter:

/usr/aw/maya/bin/mayaClockServer -h

We’ve also included an example script for using mayaClockServer. To see ademo of the clock, enter the following in the Script Editor:

mayaClockDemo

The script launches mayaClockServer using the MEL system command,defines a device named “clock,” creates three analog clock hands, andconnects the geometry to the clock.

Note

If you’ve already defined the clock device, un-define it and flush the undoqueue before running the demo script.

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Defining motion capture devicesMost motion capture devices are data-server devices. To use a data-serverdevice, you need a server. For more information on using the server for aspecific device, see the documentation provided by the device vendor.

Some devices do not need servers. These devices are installed via the IRIXdesktop. If such a device is visible to the IRIX desktop and supported byMaya, it will be listed in the Device Outliner when you start Maya.

For data-server devices, use the defineDataServer command to define thedevice in Maya. To do this, enter the following command in Maya’s ScriptEditor after you start the device server:

defineDataServer -device <deviceName> -server <serverName>;

where:

• <deviceName> is a unique device name. Choose one that will be easy foryou to remember later.

• <serverName> is the name of the communication interface defined to talk tothe server, as defined in the server setup.

For example, if you started the clock device but it did not appear in theDevice Editor, you would enter:

defineDataServer -device clock -s mayaClockServer

To undefine a device, use this syntax.

defineDataServer -device <deviceName> -undefine;

An important interaction exists between defining and un-defining dataservers and the undo queue.

When you undo a defineDataServer command, the connection with the data-server device does not break until the defineDataServer command is off theundo queue. When you undo an undefine of a data server, the connectionwith the server does not break until the command is off the undo queue. Theeasiest way to remove the command from the undo queue is to use theflushUndo MEL command.

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Motion CaptureListing devices and attachments

Listing devices and attachmentsThe Device Outliner lists the devices and their attachments.

This is the only way to see how devices are attached to their targetattributes. Since devices are not normal Maya dependency graph nodes, theydo not appear in the regular Outliner or in the Hypergraph.

Expanding device listings

The devices and their attachments appear in the following order:

• The left-most items in the Device Outliner are the devices.

• The next level shows the axes, indented to indicate their positions in thedevice hierarchy.

• The final level shows the attachments between the device and an attribute.

To expand or collapse an item:

Click the arrow to the left of the item.

To expand or collapse all of the item’s children:

Shift-click the arrow to the left of the item.

Example: Listing the mayaClock device

If you ran the mayaClockDemo MEL script, the clock name (clock) should belisted in the left column in the Device Outliner. (If it is not, follow thedirections in “Defining motion capture devices” on page 25.)

To show all of the device’s children, shift-click the arrow to the left of theclock name. The first level of children in the clock are the three axes: hours,minutes, and seconds.

Click to expand/collapse

Device

Axis

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For complex devices, an indented list of axes is displayed, each with its ownchildren. Eventually a device listing ends with attribute attachments. Theattachments describe how the device is connected to Maya attributes.

Attaching attributes and commandsYou use the Device Editor’s Attachment tab to create attachments.

There are two types of attachments: attribute attachments and commandattachments.

• An attribute attachment is a connection between an attribute and a deviceaxis.

• A command attachment is a command that is issued when a button is pressed.

Attaching attributes

Attaching attributes to device axes

To attach an attribute to a device axis:

1 Select the Maya object.

2 In the Device Outliner, select the axis you want to attach.

3 Under the Attachment tab, type the name of the Maya node that has theattribute to attach in the Node box

Attachment tabfor axis

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or

click the right mouse button in the Node box to display a pop-up menu thatlists all of the selected nodes and pick the node you want.

4 Type the name of the attribute in the Attribute box

or

click the right mouse button in the Attribute box to display a pop-up menuthat lists all of the key-able attributes for the specified node and select anattribute.

5 Specify whether you want to make the attachment per Selection or perObject.

Choose Object for most motion capture purposes. When you explicitlyconnect the device to a target attribute, that connection will always takeeffect.

Choose Selection if you want to make the connection only for the currentlyselected object. This is useful when you are interactively manipulatingobjects with an input device, but not for basic motion capture work. If youuse the Selection mode, the Node box is ignored.

6 If a device has a button, you can specify that a button is a “clutch” thatmakes the connection only while the button is pressed. Select a button nameusing the Clutch menu.

You cannot record a button press as motion capture data.

7 Click Add to make the attachment between the device axis and the attribute.

Attaching commandsYou can use command attachments with devices that have buttons. Whenyou press the button, Maya executes the command associated with thebutton.

To attach a command to a button:

1 In the Device Outliner, select a button.

2 Under the Attachment tab, type the command you wish to execute in theCommand box.

3 If you want the command to execute repeatedly while the button is pressed,turn on Continuous.

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Generally, you will want to execute the command once per button press. Todo this, turn Continuous off.

You can also execute a command every time any button is pressed orreleased, or if any axis changes on a specified device. The device must haveat least one button.

To attach a command to any device change:

1 In the Device Outliner, select a device with at least one button.

2 Under the Attachment tab, enter the command you want to executewhenever any button on the device is pressed or released or whenever anyaxis on the device changes value.

To delete a command attachment or an attribute attachment, select theattachment in the Device Outliner and click Delete.

Modifying existing attachmentsYou can also modify existing attachments using the Attachment tab.

To modify attachment mapping:

1 In the Device Outliner, select the attachment.

2 Change the attachment values.

3 Under the Attachment tab, click Update.

To delete an attachment:

1 In the Device Outliner, select the attachment.

2 Under the Attachment tab, click Delete.

Remember, a single axis may have more than one attachment.

Tip

If you accidentally delete an attachment, you can always undo the deletion.

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Mapping device dataSometimes the data coming from the device is in the wrong unit system orneeds an adjustment to its scale or offset. You can modify the scale andoffset values for incoming device data using the Mapping tab of the DeviceEditor.

There are two types of mappings: attachment mappings and device mappings.Both mappings affect the scale and offset of the device data. The device datais multiplied by the scale term and then the offset is added.

• Attachment mappings apply to attribute attachments. These mappings arerecommended for motion capture work. You can undo them.

• Device mappings apply to axes. You cannot undo them.

To modify the scale or offset of your motion capture data:

1 In the Device Outliner, select the axis or attachment you want to modify.

Select an axis if you want the Mapping tab to control a device mapping.

Select an attachment if you want the Mapping tab to control an attachmentmapping.

2 Under the Mapping tab, select Absolute or Relative mapping.

Important

Using device and attachment mapping together is error-prone and mayproduce unintentional results.

Mapping tab

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With Absolute mapping, motion is scaled and offset with respect to the origin.If you move a device a foot away from the origin, the target attribute alsochanges its value to be one foot away from the origin. Absolute mapping isuseful for motion capture.

With Relative mapping, motion is adjusted relative to the last device position,without regard to the origin. If you move a device one foot to the right, thetarget attribute moves one foot to the right.Relative mapping is useful fordesktop input devices that always return to some resting position.

3 If you are working with device mapping, choose whether you want to applyyour mapping to World space or View mode.

Select World for motion capture work.

If View mode is used, the device coordinates are translated into the space ofthe active camera.

Saving attachmentsSince devices are not defined as dependency graph nodes, their definitions,attachments, and mappings are not saved in Maya files.

Creating an attachments script lets you reload the attribute attachments,command attachments, and mappings when you need them. This saves youhaving to attach the device to each of its target attributes every time youload a file. You must define the device before running the attachment script.

The MEL script will remake all of the attribute attachments, commandattachments, and mappings, provided the device is defined and the targetattributes and nodes have the same names as they did when you saved thescript.

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To create an attribute attachments script:

1 In the Device Outliner, select the device, its axes, or its attachments.

2 Under the Controls tab, click Save Attachments.

3 Select a path and name for the attachments MEL script.

Be sure you save the script in your scripts path so Maya can see it when youwant to reattach your scene.

4 Click OK.

The next time you load the scene, define the device, if needed, and run theattachments script from the Script Editor.

Click here to savethe script

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Capturing motionFor each motion to capture, there are three different phases of the captureprocess: rehearse, record, and review. For each of these steps, you’ll use theDevice Editor’s Controls tab.

Rehearsing the motionYou may wish to have the performer rehearse the motion you’re interestedin before you record. During this rehearsal phase, any of the actor’squestions can be worked out to perfect the move. If the scene is not tooheavy, you may be able to view the motion in real time.

Any animation curves attached to the target attributes are not affected by theRehearse mode.

To rehearse the motion:

1 Under the Controls tab, select Rehearse.

2 Select Enable Monitor to specify that the target attributes are getting livedata from the device.

When you switch from other phases, this step is performed automatically forall devices.

Recording the motionThe settings for beginning recording are also under the Controls tab.

To record the motion:

1 Under the Controls tab, turn on Enable Record for each device you want torecord.

2 Make sure the Recording Duration box has enough recording time (inseconds) for your planned motion.

We recommend you add a few more seconds to the duration and startrecording before the actor begins a move.

3 Select Record.

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All the record-enabled devices begin recording data, using the current timeas a start time for the recording.

Once the duration is met, the recording stops and advances to the reviewphase. At this point, the data is not yet part of your Maya animation and isnot saved to a Maya file.

Data that you can preview or convert into animation curves is called a take.

4 When you are ready to convert the take to animation curves, click ApplyTake.

Reviewing the motionIn the review phase, Maya applies the motion data you have recorded to thetarget attributes. Your preview data is applied to all devices and axes thathave Apply Take enabled (as indicated by Enable Apply Take). Animationcurves that are attached to the target attributes are not affected at this time.

Tip

The recording frequency is determined by the device, not by the frame rateof Maya.

Tip

To stop a recording before the duration expires, select either Rehearse orReview under the Controls tab.

• Review will take you to the review mode, the same as if the durationexpired.

• Rehearse will not bring the device data into Maya.

If you accidentally chose Rehearse and want to see the motion in yourscene, click the Preview or Apply Take buttons. Click Preview to create apreview version of the take; click Apply Take to make an animation curveversion of the take.

Important

If a device has a take and you select Record, that take is lost unless youfirst click Write Take to save it or Apply Take to convert it to animationcurves.

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During the review phase, you can click Preview to view the take in apreview form; this does not change the data.You can also click Apply Taketo convert the take to animation curves in the review phase.

Viewing a take in preview formA preview is done automatically when you enter the review phase. This letsyou review the newly captured motion faster than by using Apply Take andleaves the animation curves unchanged. Preview data is not visible in theGraph Editor.

To view a take in preview form:

Under the Controls tab, click Preview.

When an attribute attachment is formed, a node (blendDevice) is attached tothe target attribute. The blendDevice node determines whether you willview live device data (Enable Monitor) or the animation curve that isattached to the attribute.

In this form, the data is stored in the blendDevice node. Playing over therecorded time range will show the newly recorded data, leaving anyanimation curves unchanged.

If you save your scene to a Maya file, preview data is not saved as part of thescene. To save preview data, use the Write Take button (as described in“Saving files to disk” on page 36).

Converting a take to animation curves

To convert the take to animation curves:

Under the Controls tab, click Apply Take.

When you convert the take to animation curves, the new data replaces anyexisting animation curves. Older data outside of the newly recorded timerange still exists, but any old data within the recorded time range does not.

Note

If you are doing a batch render, be sure to save the motion as animationcurves (using Apply Take). Otherwise the motion will not be part of therender.

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When the take is converted to either preview form or animation curves, alldevice mappings, attachment mappings, filters, and resamplers are appliedto the take data.

Changing the attachment and device mappingsYou can change the scale and offset values in a mapping without affectingthe preview data or animation curves.

To change the attachment and device mappings on the take:

1 Change the values using the Mapping tab (as described in “Modifyingexisting attachments” on page 29).

2 Reapply the take by clicking Preview or Apply Take.

Saving files to diskYou can write out a take as an ASCII file, then read the file back into thescene and review it later.

Motion capture files use the .mov file format. This file format is called“move” in the file browser. It is not related to any movie file format. Forinformation on the .mov file format, see the online document, Maya FileFormats.

Since a single scene may have dozens of motions, you probably do not wantto save each move as a separate Maya file, especially after you have selectedthe final versions of the motion. It is much easier to save only the motion asa separate file.

To save a take to disk:

1 Under the Controls tab, click Take File.

Maya will display a file browser.

2 If this is a new file, specify a path using the file browser and specify a newfilename.

The base filename appears in the box. From now on, if the Take box changes,the path stays the same; only the filename changes.

3 Once you’ve specified a valid filename, click Write Take to save the take todisk.

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A take name is required for each device.

Freeing memoryAfter applying the recorded data, the take data is still in a take buffer. Forsmall takes this may not be a problem, but for large takes you may want tofree this memory.

To free the take data for all devices:

• Under the Controls tab, click Clear.

You cannot undo this action.

Numbering takesA particular motion may require three takes or more. Since it may bedifficult to determine which take is best as you record and coming up withunique names for each version of the same move is error-prone, Mayafeatures an easy way to number your takes.

Take numbering inserts a number between the move name and its extension(by default, .mov). This number can be incremented to form a take numberfor that move. The take filename is constructed by inserting the value of theNumber box before the extension of the name in the Take box.

For example, if the Take box displays clock.mov and the Number boxdisplays a value of 2, the file is saved as clock.002.mov.

Note

If you want to save a take every time you enter the review phase, selectWrite Take on Review under the Controls tab.

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To number your takes:

1 Under the Options tab, select Numbered Takes.

Whenever the Take box changes, the Number box is reset to the value inStarting Take.

2 If you want to automatically increment the take number whenever a take iswritten, also select Auto-Increment.

3 When your motion data looks good and you want to convert it to animationcurves, click the Apply Take under the Controls tab.

Viewing numbered takes (Example)

Take numbering also makes it easier to view different versions. For example,if you have five versions of the clock.mov file that used take numbering, youcould view them by completing the following steps:

1 Select clock.001.mov using the take browser (the Take File button).

2 Read the takes into the device by clicking Read Take under the Controls tab.

3 See the first take in Maya by clicking Preview or Apply Take.

4 See the second take by changing the value in the Number box to 2,thenclicking Read Take and clicking Preview.

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Using filters and resamplersYou can use filters and resamplers to affect your motion capture data. Filtersand resamplers let you achieve effects such as demangling Euler angles orresampling data to a specific frequency with a given kernel. You use theFilters tab to create filters and resamplers.

Filters and resamplers are applied when you create a Preview, Apply Take,or Review. You cannot apply filters and resamplers while you monitordevices, only when you convert your data to animation curves using theApply Take button or convert it to blendDevice nodes using the Previewbutton.

A resampler may change the temporal values of the data; a filter will not.

To create a filter or resampler:

The same procedure applies to both filters and resamplers.

1 Place the pointer in the Active or Inactive Filters (or Resamplers) list andclick the right mouse button.

Maya displays a list of available filters (or resamplers).

2 Select the filter (or resampler) name in the list to create it.

The filter or resampler name appears in the Active or Inactive Filters list.

Filter settings

Use these buttons tochange betweenactive and inactivelist.

Resampler settings

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3 To view or change the attributes of a filter or resampler, double-click itsname in the list.

The Attribute Editor for the filter appears.

4 To move an item back and forth between the Active and Inactive lists, clickits name in the list and use the << and >> buttons.

Reviewing takesIt is not practical to connect a motion capture device to every machine onwhich you want to view captured motions. Instead, you use a virtual device.A virtual device behaves like a real device in review mode. You can makethe same attachments to a virtual device as to a real device. You can readtake data into a virtual device and apply it to the target attributes. Virtualdevices cannot have buttons.

To define a virtual device based on a real device:

1 Select the real device in the Device Outliner.

Under the Controls tab, click Save Virtual Device.

2 Select the path and specify a MEL script name.

When you execute the MEL script, a virtual device is defined with the samename as the real device. If you have attachment scripts, they will work withthe virtual device without any changes.

You can use virtual devices to import numeric data into Maya. In manycases, you can use the movIn command. However, if you are using filters orresamplers, we recommend using a virtual device.For more information, seethe documentation for the defineVirtualDevice command.

To read data into a virtual device:

Reading data into a virtual device is the same as reading in data to a realdevice.

1 Under the Controls tab, click Take File.

2 Select the take using the browser that appears.

3 Click Read Take to load the take.

4 Click Preview or Apply Take to make the data visible in your animation.

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To specify how Maya interprets incoming take data:

Use the Options tab to set the units used in the take and time-stamping ofthe data.

If a take has time-stamp data, turn on Time Stamps in the Read TakeOptions section.

If you want to ignore time-stamp information, select Use Frequency in theRead Take Options section and type a value in the Frequency box, in Hertz.

Since the .mov file format does not contain information about how data is tobe interpreted, the order of data in the take file is important. The order ofcolumns of data in the file must match the order of axes in the device.

If you are creating a virtual device by hand, the order of definition isextremely important and must match your data.

If time stamps were used with the write take, the first column of data is thetime-stamp information. The take is applied with the starting time as thestarting time of the recording, if time stamps were used.

If you turn on Use Current Time As Apply Take Start Time under theControls tab, Maya uses the current time as the start time for the take whenyou click Preview or Apply Take.

Using multiple devicesYou can record and work with many devices simultaneously.

Use the Controls tab to set recording options for each device. To view adevice’s current settings, select the device name in the Device Outliner, thenselect the Options tab.

• If you do not wish to record data for a device, turn off Enable Record in theControls tab.

• If you do not want to apply data to the target attributes of a device, turn offEnable Apply Take under the Controls tab.

To record multiple devices:

1 Under the Controls tab, turn on Write Take on Review.

2 Specify a take name for each device.

3 Under the Options tab, select Numbered Takes and Auto-Increment.

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With this method, each device automatically saves unique files for each takeand you don’t have to manually change the take number and take names.

Performing full-body motion captureThe most important task of any motion capture is to plan every step inadvance. This is especially true for a large project.

To create a full-body motion capture:

1 Select a motion capture device.

2 Choose a method for calculating the motion.

The method is device-dependent and may use inverse kinematics, forwardkinematics, constraints, or a combination of the three.

3 Build a skeleton based on the actor’s proportions. If possible, digitize theactor’s joint positions with your motion capture device.

4 Attach the performance skeleton to the device.

5 Connect the performance skeleton to the character skeleton.

6 Rehearse the actions to be performed.

7 Record the motion.

8 Review the recorded motion and insert it into your scene.

Tips for full-body motion captureWith full-body motion capture, carefully thought-out sensor placement andskeletal design are essential.

Using an optical system

If you use an optical system, just bring the data into Maya. You will need tomake a virtual device to read in the motion. See the documentation for thedefineVirtualDevice command.

We recommend using a single format for all of the motion you import intoMaya. You can write a MEL script to define the virtual device that matchesthe data. With this method, you have to explicitly define the virtual deviceonly once; other times you can run the script that calls the virtual devicedefinition.

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If no filtering is needed, try using the MEL movIn command. This does notrequire the construction of a virtual device.

To use all of the take management functionality and filters, you must definea virtual device and make attachments to it. Since most optical systems letyou solve for joint angles, you can use forward kinematics. For a skeletonconstructed with the same orientation as the solved optical skeleton, justattach the device to the rotations of the joints.

Using a magnetic capture system

For a magnetic capture system, connecting the sensor axes to handles of RPof MC IK solvers works well.

Tips for working with full-body motion capture data

• Work with a skeleton that has the same proportions as the actor. You cancreate a character based on the actor’s body. If you are using a magneticsystem, you can place sensors on opposite sides of each of the actor’s joints.Record the sensor’s location at each placement. You can construct a skeletonthat has joints located between opposing sensor positions. If magnetic noiseis not a problem, this will produce an accurate copy of the actor’s skeleton.

• If this is not possible or the character is dissimilar to the actor, create askeleton based on the actor and solve for that skeleton. You can useconstraints, expressions, and connections to map joint rotations and the rootposition from the actor skeleton to a character.

• When you select a device using the Device Outliner, the Controls tab willshow the take information for that device.

• It is worth taking extra time to ensure that your data is as clean as possible.For option systems, this mean rigorous calibration of both the space and theactor. For magnetic systems, the freer the space of magnetic noise, the betterthe result.

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Index

Index

Aabsolute mapping 31Active Filters list 39Active Resamplers list 39adding constraint objects 7adjusting target weights 8aim constraints 15aim vectors 18

default values 18Apply Take button 34, 35, 38attachment for motion capture 22attachment mappings 30Attachment tab 29attachments

command 28deleting 29listing 26making 27, 28modifying 29saving 31, 32

attachments script 31Attachments tab 27Attribute box 28attributes

attaching 27Auto-Increment option 38, 41axis 22

motion capture 22

Bbuttons

attaching 28constraint reset 8motion capture 22

Ccapturing motion 33changing device mapping 36channel box

setting target weight 8, 9Clear button 37clock server 26clutch 22commands

attaching 28attaching commands 28

constraint targetsadding 7removing 8

constraintsaim 15basic 5basic procedure 7IK handle 13orientation 5, 14point 11pole vector 13position 5, 11reset button 8scale 6, 19surface 12surface normal 16tangent 17

Controls tab 32, 33, 35, 36, 37,40

converting takes to curves 35curves

converting takes to 35removing animation 8tangent constraints 17

Ddata server devices 25

default valuesaim vectors 18up vectors 18world up vectos 19

device attachmentssaving 31, 32

device axis 22Device Editor 23device mappings 30, 36Device Outliner 23, 26devices

attaching 29listing 26mapping 36mappings 30motion capture 22multiple motion capture 41

EEnable Apply Take option 34, 41Enable Monitor option 33Enable Record button 41Enable Record option 33Euler angles 39expressions

driving multiple targetweights 11

Ffilters

motion capture 36, 39Freeing memory

motion capture 37freeing memory

motion capture 37full-body motion capture 42

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2 Using Maya: Animation

Hhandler mappings 36

IIK handle constraints 13Inactive Filters list 39Inactive Resamplers list 39

Mmagnetic capture systems 43mapping 30

absolute 31changing 36device 36handler 36relative 31

Mapping tab 36matching orientations 14mayaClockServer program 26memory

freeing 37motion

capturing 33motion capture 21

basic procedure 21device 22file format 36freeing memory 37full-body procedure 42magnetic systems 43recording 33rehearsing 33saving files to disk 36servers 22stopping recording 34terminology 22

.mov file format 36

multiple devicesmotion capture 41

multiple target weightsusing expressions 11

multiple targetsadjusting weights 8weighted average 7

Nnode 35Node box 27normal

constraining 16Numbered Takes option 37, 38,

41numbering takes 37, 38

OObject option 28objects

definition 6selection 6

offset valuesmapping 30, 36

optical systems 42Options tab 41orientation

constraints 5, 14matching another object 14

OutlinerDevice 23, 26

Ppoint constraints 11pole vector constraints 13position constraints 5, 11

Preview button 35, 40previewing takes 35

RRead Take button 40Record button 33, 34recording

motion capture 33multiple devices 41stopping 34

Recording Duration box 33Rehearse button 33rehearsing motion capture 33relative mapping 31removing constraint objects 8resamplers 36, 39review phase 34

SSave Attachments button 32Save Virtual Device button 40saving device attachments 31,

32saving motion capture files 36scale

constraints 6, 19scale values

mapping 30, 36script

attachments 31device attachments 32

selecting constraint objects 6selecting constraint targets 6Selection option 28servers

clock 26motion capture 22

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Index

setting target weights 9channel box 8, 9

skeletonsproportions for 43

Starting Take box 38stopping motion capture

recording 34surface

constraining to a tangent 17constraining to normal 16constraints 12

TTake File button 40takes

converting to curves 35definition 34freeing data 37numbering 37, 38previewing 35reviewing later 40viewing 35

tangentconstraining 17

target weightsadjusting 8setting 9

targetsdefinition 6selection 6using multiple 7, 8

Terminology for motioncapture 22

Time Stamps option 41

Uup vector

aim 17

up vectors 18controlling 17default values 18setting world up type 18world 17

Use Current Time As Apply TakeStart Time option 41

Use Frequency option 41

Vview mode 31Viewing takes in preview form 35virtual devices 40, 43

Wworld space 31world up objects 19world up type

aligning up vector 18none 19object 18object rotation 18scene 18vector 18

world up vectorsdefault values 19

Write Take button 34Write Take on Review option 37,

41

YY-axis

orientation 17