Pose Solver Node

MediaPipe4U uses the MediaPipePoseSolver Animation Blueprint node to calculate character-joint rotations from capture data and synchronize the subject's pose with a 3D character.

Install the Node

1. Add MediaPipePoseSolver to the Animation Blueprint.
2. Configure its primary behavior.

MediaPipe4U calculates joint rotations and drives the 3D character into a pose approximating the subject.

Parameters

Parameter	Type	Description
Alpha	float (0-1.0)	Same as Alpha on standard Animation Blueprint nodes.
Smooth	float (0-1.0)	Motion smoothing. Higher values reduce jitter but lower responsiveness. Use lower values for fast motion and higher values for slow sources.
LockArms	bool	Locks the chain from upper arms to hands. When true, Shoulder, UpperArm, LowerArm, and Hand do not participate.
LockLegs	bool	Locks the chain from thighs to feet.
LockHips	bool	Locks the pelvis, usually the root, preventing whole-body rotation.
LockSpine	bool	Locks the spine, preventing upper-body rotation.
LockChest	bool	Locks the chest. Note: LockSpine also locks the chest.
LockHead	bool	Locks the head.
LockHand	bool	Locks wrists and fingers. Note: LockArms also locks hands.
LockElbow	bool	Locks elbows. Note: LockArms also locks elbows.
LockKnee	bool	Locks knees. Note: LockLegs also locks knees.
LockFoot	bool	Locks ankles. Note: LockLegs also locks ankles.
UseLegIK	bool	Uses leg IK to correct knee twisting. Normally enabled, though motion may be less exact.
UseArmIK	bool	Uses arm IK to correct elbow twisting. Normally enabled, though motion may be less exact.
KalmanQ	float	Kalman filter Q; do not change unless familiar with Kalman filtering.
KalmanR	float	Kalman filter R; do not change unless familiar with Kalman filtering.
Optimize	bool	Whether to perform additional optimization.
CountdownCalibrationEnabled	bool	Defaults to false; whether to calibrate pose when the countdown ends.
Calibration	PoseCalibrationFlags	Joints included during calibration.
UseSpinePitch	bool	Whether to use spine pitch rotation.
HipPitchSpanAngle	int	Angle from 0 to 180 controlling pelvis-rotation intervals.
bFixMediaPipePose	bool	Whether to correct details in raw MediaPipe capture data.
UpperBodyLocks	struct	Locks upper-body pitch, yaw, and roll.
TwistCorrectionSettings	struct	Joint twist-correction weights.

Arm IK

With UseArmIK enabled, TwoBone IK drives the arm from upper arm to wrist instead of directly rotating bones, primarily preventing elbow twisting. If the pose is already good without Arm IK, disable it for a pose closer to the source.

Leg IK

With UseLegIK enabled, TwoBone IK drives the leg from thigh to ankle instead of directly rotating bones, primarily preventing knee twisting. If the pose is already good without IK, disable it for a pose closer to the source.

Pose Calibration

Image-based tracking can bend knees or the spine because of vision-algorithm limitations. MediaPipe4U therefore provides initial-pose calibration.
By default, a countdown starts with capture and calibrates body joints when it ends.

Set the duration with CalibrateCountdownSeconds on MediaPipeAnimationInstance.

Tip

MediaPipe4U supports two pose-calibration modes:

1. CountdownOnStart: start a countdown with capture and calibrate automatically at its end.
2. Manual: call CalibratePose on MediaPipeAnimationInstance manually.

Set CountdownCalibrationEnabled on Pose Solver to control whether countdown completion performs pose calibration.

For more information, read Calibration.

Adjust Joint Locks

Tip

Dynamically changing joint locks invalidates pose calibration.

Recalibrate manually after changing locks at runtime; see Calibration.

Pose Optimization

Capture accuracy, occlusion, and IK can produce imperfect details. Set Optimize to true to improve them and use Optimize Settings to select optimizations:

Current and planned optimizations:

• Ankle rotation correction
• Knee pole-vector correction
• Shoulder-motion compensation
• Foot rotation correction

New optimizations are added over time; enabling optimization is recommended.

Extreme-pose comparison after optimization:

Tip

Optimize adjusts unreasonable joint rotations. Disable it if it causes pose problems.

Spine Rotation Mode (Beta)

By default, MediaPipe4U rotates the body through the pelvis. Pelvis rotation affects the whole body and capture jitter may cause unstable ankles. Spine rotation mode greatly improves this:

1. Enable UseSpinePitch on Pose Solver.
2. Set an appropriate HipPitchSpanAngle for the model.

Meaning of HipPitchSpanAngle:

Pelvis Pitch ranges from -180 to 180 degrees. HipPitchSpanAngle divides it into steps; for example, 30 degrees:

Pelvis rotation changes only at specific steps such as 0, 30, 90, 120, 150, 180, -30, -90, -120, and -150; the spine supplies remaining rotation. This reduces pelvis changes and stabilizes ankles. Example for 0-180 degrees:

Body Pitch	Pelvis Angle	Spine Angle
0 - 29	0	0- 29
30 - 59	30	0- 29
60 - 89	60	0- 29
90 - 119	90	0- 29
120 - 179	120	0- 29
180	180	0

Warning

Spine rotation mode is a beta feature. Disable it if it causes problems.

Skeleton designs differ; tune the span for your model.

Incorrect spans can twist the spine. Smaller spans reduce twisting but increase pelvis switching and foot instability; larger spans improve foot stability.

Upper-Body Locks

Use UpperBodyLocks on Pose Solver to lock any of the upper body's three axes.

The axes are defined as follows: