Location Solver Node¶

MediaPipe4U uses the MediaPipeLocationSolver Animation Blueprint node to calculate character translation from motion-capture data.

Tip

Moving the character moves its root bone, the first bone in the hierarchy.

MediaPipeLocationSolver requires location calibration before it can work.

Install the Node¶

Add MediaPipeLocationSolver to the Animation Blueprint.
Configure its primary behavior on the node.
Select the node and configure details in the Details panel.

MediaPipe4U now calculates subject translation and moves the 3D character on the X, Y, and Z axes.

The following settings adjust location solving. The main concerns are movement-axis control, speed, and ground alignment. Many other properties are shared by all MediaPipe4U nodes through their base class.

Basic Parameters¶

These commonly used properties cover most scenarios.

Property	Default	Description
Smooth	0.3	Smoothing applied to capture data, from 0 to 1. Higher values are smoother.
LockHorizontalMove	false	When true, prevents horizontal left/right movement.
LockVerticalMove	false	When true, prevents vertical up/down movement.
LockForwardMove	false	When true, prevents forward/backward movement.
UseGroundIK	true	Whether to use Ground IK, described below.
SmoothSpeed	200	Movement smoothing speed in centimeters per second, preventing excessive movement when video changes suddenly. 0 means unlimited.
DepthInterpSpeed	0.5	Rate at which the estimated subject-to-camera distance changes. This affects depth calculation and normally needs no adjustment.
MovementScale	Vector(1,1,1)	Scales translation on three axes. For a character facing Y, X is horizontal, Y is forward/backward, and Z is vertical.
CountdownCalibrationEnabled	true	Whether to calibrate location when the countdown ends.

Location Calibration¶

If CalibrationPolicy on MediaPipeAnimInstance is Manual (the default), you must call CalibrateLocation on MediaPipeAnimationInstance before the location solver works.

With CountdownOnStart, capture automatically starts a countdown and captures one video frame as the position reference when it ends.

With CountdownOnStart, set the duration through CalibrateCountdownSeconds.

Tip

MediaPipe4U supports two location-calibration modes:

Countdown: after a countdown, automatically capture a frame from the image source for calibration.
Manual: call CalibrateLocation on MediaPipeAnimationInstance to capture the current frame manually.

Use CountdownCalibrationEnabled on MediaPipeLocationSolver to control automatic countdown calibration.

For more information, read Calibration.

Ground IK¶

A monocular camera cannot accurately obtain depth. MediaPipe4U's calibration-free design also lacks camera intrinsics and a rotation matrix, so pixel coordinates cannot be mapped directly to spatial coordinates and character location may drift. Vertical drift can make the character float or sink into the ground. The built-in Ground IK solver aligns the feet with the ground.

Tip

Ground IK is not a universal solution and cannot guarantee perfect results.

The easiest way to get started is to watch a tutorial:

How Ground IK Works¶

Casts rays toward the ground
Calculates foot-to-ground distance from each foot bone
Moves the pelvis to eliminate that distance
Applies IK to the thigh-to-ankle chain for a natural pose

Warning

Ground IK uses ray traces and rays from the legs must collide only with the ground. Create a dedicated Collision Channel that ignores all other collision, especially the Character capsule. See Unreal Engine collision-channel documentation.

Select the location solver node and adjust Ground IK in Details.

Most defaults are reasonable. Usually, adjust only:

FeetDampingDistance
JumpVelocityThreshold
FeetSmoothSpeed
PreventSlidingDistance

Complete Parameter Reference¶

MoveRoot¶

Ground IK moves the pelvis by default. Set this to true to move the root bone instead. Default: false

RotateFootAlignGround¶

Whether to rotate ankles to align feet with the ground. Disable this when inappropriate, for example with high heels.
Default: true

FeetRollSmooth¶

Ankle Roll smoothing from 0 to 1; higher values are smoother.
Default: 0.6

FeetPitchSmooth¶

Ankle Pitch smoothing from 0 to 1; higher values are smoother.
Default: 0.8

CollisionChannel¶

Collision channel used for ray traces. Ensure foot rays collide only with the ground.

HipsRotationMultiplier¶

Controls slight pelvis rotation when the surface normal changes as the pelvis moves.

MaxSquashIterations¶

Leg IK iterations when pelvis movement compresses the legs.

MaxStretchIterations¶

Leg IK iterations when pelvis movement stretches the legs.

FeetSmoothSpeed¶

Incremental nonlinear speed, in centimeters per second, used when moving a Foot bone toward the ground. Decrease it if lifting or lowering is too fast; increase it if too slow.

FeetSmoothAngularSpeed¶

Incremental angular speed, in degrees per second, used when rotating a Foot bone to align with the ground.

FeetDampingDistance¶

Foot-lift damping height in centimeters. Below this height, the foot remains attached to the ground. Smaller values make lifting more sensitive. Decrease it if the foot cannot lift; increase it if the foot lifts unexpectedly.

JumpVelocityThreshold¶

Jump-velocity threshold in centimeters per second. Only movement above this value is treated as jumping, gradually reducing foot damping for takeoff. Lower values are more sensitive to small jumps. Increase it if the character often leaves the ground; decrease it if the character cannot jump.

InertiaSmoothFactor¶

Inertia-smoothing factor used to remove movement oscillation through incremental nonlinear damping. Higher values provide more smoothing.

FeetVerticalOffset¶

Static vertical foot offset in centimeters. Use it when IK leaves feet sunk or floating, possibly because the modeled feet and root bone are not coplanar. Positive values push upward; negative values push downward.

bRotateFootAlignGround¶

Whether to rotate ankles so soles align with the ground. Default: true

MoveRoot¶

Ground IK moves the pelvis by default to remove floating or sinking. Set true to move the root bone instead; not recommended. Default: false

PreventSlidingDistance¶

Distance in centimeters within which foot sliding is suppressed as much as possible. Default: 5

Debug Drawing¶

Ray-collision or foot-position issues can cause Ground IK failure. Enable DebugDraw to display key solving points.

Select MediaPipe Location Solver in the Animation Blueprint.
Enable DebugDraw in Details.
Run the application and start motion capture.

Tip

If DebugDraw on MediaPipeAnimationInstance is false, node-level DebugDraw has no effect.

After capture starts:

Annotations:

Green box: Foot-bone position after Ground IK.
Blue box: Foot-bone position before Ground IK.
Short red line: horizontal sole plane, which should be parallel to the ground.
Ground-detection ray: green means a hit; red means no hit.
Yellow point: ray-hit location, normally on the ground.