# LeapHand¶

Properties:

Methods:

class LeapHand

The LeapHand class reports the physical characteristics of a detected hand.

Hand tracking data includes a palm position and velocity; vectors for the palm normal and direction to the fingers; properties of a sphere fit to the hand; and lists of the attached fingers.

Note that LeapHand objects can be invalid, which means that they do not contain valid tracking data and do not correspond to a physical entity. Invalid LeapHand objects can be the result of asking for a Hand object using an ID from an earlier frame when no hand objects with that ID exist in the current frame. A hand object created from the LeapHand constructor is also invalid. Test for validity with the LeapHand isValid function.

Since 1.0

Public Functions

- (LeapFinger *) finger:(int32_t) fingerId

The LeapFinger object with the specified ID attached to this hand.

Use this [LeapHand finger:] function to retrieve a LeapFinger object attached to this hand using an ID value obtained from a previous frame. This function always returns a LeapFinger object, but if no finger with the specified ID is present, an invalid LeapFinger object is returned.

LeapFinger *knownFinger = [hand finger:fingerID];


Note that ID values persist across frames, but only until tracking of a particular object is lost. If tracking of a finger is lost and subsequently regained, the new LeapFinger object representing that finger may have a different ID than that representing the finger in an earlier frame.

Return
The LeapFinger object with the matching ID if one exists for this hand in this frame; otherwise, an invalid LeapFinger object is returned.
Since 1.0
Parameters
• fingerId -

The ID value of a LeapFinger object from a previous frame.

- (LeapPointable *) pointable:(int32_t) pointableId

The LeapPointable object with the specified ID associated with this hand.

Use this [LeapHand pointable:] function to retrieve a LeapPointable object associated with this hand using an ID value obtained from a previous frame. This function always returns a LeapPointable object, but if no finger with the specified ID is present, an invalid LeapPointable object is returned.

LeapPointable *knownPointable = [hand pointable:pointableID];


Note that ID values of fingers are based on the hand ID. Hand IDs persist across frames, but only until tracking of that hand is lost. If tracking of a hand is lost and subsequently regained, the new LeapHand object representing that hand will have a different ID than that representing the hand in an earlier frame. Thus the IDs for the fingers on the hand will also change.

Return
The LeapPointable object with the matching ID if one exists for this hand in this frame; otherwise, an invalid LeapPointable object is returned.
Since 1.0
Parameters
• pointableId -

The ID value of a LeapPointable object from a previous frame.

- (float) rotationAngle:(const LeapFrame *) sinceFrame

The angle of rotation around the rotation axis derived from the change in orientation of this hand, and associated fingers, between the current LeapFrame and the specified LeapFrame.

LeapFrame *lastFrame = [controller frame:1];
float angleOfRotationSinceLastFrame =
[hand rotationAngle:lastFrame];


Return
A positive value representing the heuristically determined rotational change of the hand between the current frame and that specified in the sinceFrame parameter.
Parameters
• sinceFrame -

The starting LeapFrame for computing the relative rotation.

- (float) rotationAngle:(const LeapFrame *) sinceFrame axis:(const LeapVector *) axis

The angle of rotation around the specified axis derived from the change in orientation of this hand, and associated fingers, between the current LeapFrame and the specified LeapFrame.

LeapFrame *lastFrame = [controller frame:1];
float angleOfRotationAroundYSinceLastFrame =
[hand rotationAngle:lastFrame axis:LeapVector.yAxis];


Return
A value representing the heuristically determined rotational change of the hand between the current frame and that specified in the sinceFrame parameter around the specified axis.
Parameters
• sinceFrame -

The starting LeapFrame for computing the relative rotation.

• axis -

A LeapVector representing the axis to measure rotation around.

- (LeapVector *) rotationAxis:(const LeapFrame *) sinceFrame

The axis of rotation derived from the change in orientation of this hand, and associated fingers, between the current LeapFrame and the specified LeapFrame.

LeapFrame *lastFrame = [controller frame:1];
LeapVector *axisOfRotationSinceLastFrame =
[hand rotationAxis:lastFrame];


Return
A LeapVector containing the normalized direction vector representing the heuristically determined axis of rotational change of the hand between the current frame and that specified in the sinceFrame parameter.
Parameters
• sinceFrame -

The starting LeapFrame for computing the relative rotation.

- (LeapMatrix *) rotationMatrix:(const LeapFrame *) sinceFrame

The transform matrix expressing the rotation derived from the change in orientation of this hand, and associated fingers, between the current LeapFrame and the specified LeapFrame.

LeapFrame *lastFrame = [controller frame:1];
LeapMatrix *rotationSinceLastFrame =
[hand rotationMatrix:lastFrame];


Return
A transformation LeapMatrix representing the heuristically determined rotational change of the hand between the current frame and that specified in the sinceFrame parameter.
Parameters
• sinceFrame -

The starting LeapFrame for computing the relative rotation.

- (float) rotationProbability:(const LeapFrame *) sinceFrame

The estimated probability that the hand motion between the current LeapFrame and the specified LeapFrame is intended to be a rotating motion.

LeapFrame *lastFrame = [controller frame:1];
float rotationIntent =
[hand rotationProbability:lastFrame];


Return
A value between 0 and 1 representing the estimated probability that the hand motion between the current frame and the specified frame is intended to be a rotating motion.
Parameters
• sinceFrame -

The starting LeapFrame for computing the relative rotation.

- (float) scaleFactor:(const LeapFrame *) sinceFrame

The scale factor derived from this hand’s motion between the current LeapFrame and the specified LeapFrame.

LeapFrame *lastFrame = [controller frame:1];
float scaleChangeSinceLastFrame =
[hand scaleFactor:lastFrame];


Return
A positive value representing the heuristically determined scaling change ratio of the hand between the current frame and that specified in the sinceFrame parameter.
Parameters
• sinceFrame -

The starting LeapFrame for computing the relative scaling.

- (float) scaleProbability:(const LeapFrame *) sinceFrame

The estimated probability that the hand motion between the current LeapFrame and the specified LeapFrame is intended to be a scaling motion.

LeapFrame *lastFrame = [controller frame:1];
float scaleIntent = [hand scaleProbability:lastFrame];


Return
A value between 0 and 1 representing the estimated probability that the hand motion between the current frame and the specified frame is intended to be a scaling motion.
Parameters
• sinceFrame -

The starting LeapFrame for computing the relative scaling.

- (LeapVector *) translation:(const LeapFrame *) sinceFrame

The change of position of this hand between the current LeapFrame and the specified LeapFrame.

LeapFrame *lastFrame = [controller frame:1];
LeapVector *translationSinceLastFrame =
[hand translation:lastFrame];


Return
A LeapVector representing the heuristically determined change in hand position between the current frame and that specified in the sinceFrame parameter.
Parameters
• sinceFrame -

The starting LeapFrame for computing the translation.

- (float) translationProbability:(const LeapFrame *) sinceFrame

The estimated probability that the hand motion between the current frame and the specified LeapFrame is intended to be a translating motion.

Return
A value between 0 and 1 representing the estimated probability that the hand motion between the current frame and the specified frame is intended to be a translating motion.
Parameters
• sinceFrame -

The starting LeapFrame for computing the translation.

Property

- (LeapArm *) arm
arm

The arm to which this hand is attached.

If the arm is not completely in view, Arm attributes are estimated based on the attributes of entities that are in view combined with typical human anatomy.

Return
The Arm object for this hand.
Since
2.0.3

- (LeapMatrix *) basis
basis

The orientation of the hand as a basis matrix.

The basis is defined as follows:

xAxis Positive in the direction of the pinky

yAxis Positive above the hand

zAxis Positive in the direction of the wrist

Note: Since the left hand is a mirror of the right hand, the basis matrix uses the left-hand rule for left hands.

LeapFrame *frame = [leap frame:0];
for (LeapHand *hand in [frame hands]) {
LeapMatrix *handTransform = [[LeapMatrix alloc] initWithXBasis:hand.basis.xBasis
yBasis:hand.basis.yBasis
zBasis:hand.basis.zBasis
origin:hand.basis.origin];
handTransform = [handTransform rigidInverse];

LeapInteractionBox *iBox = frame.interactionBox;
for (LeapFinger *finger in hand.fingers)
{
LeapVector *transformedPosition = [handTransform transformPoint:finger.tipPosition];
LeapVector *transformedDirection = [handTransform transformDirection:finger.direction];
}


Return
The basis of the hand as a matrix.
Since
2.0

- (float) confidence
confidence

Rates how well the internal hand model fits the observed data.

The confidence level ranges between 0.0 and 1.0 inclusive, with 1.0 representing high confidence.

float modelToDataFitQuality = hand.confidence;


Return
A confidence rating between 0 and 1.
Since 2.0

- (LeapVector *) direction
direction

The direction from the palm position toward the fingers.

LeapVector *direction = hand.direction;


The direction is expressed as a unit vector pointing in the same direction as the directed line from the palm position to the fingers.

Return
The LeapVector pointing from the palm position toward the fingers.
Since 1.0

- (NSArray *) fingers
fingers

The list of LeapFinger objects detected in this frame that are attached to this hand, given in arbitrary order.

NSArray *fingerList = hand.fingers;


The list can be empty if no fingers attached to this hand are detected.

Return
An NSArray containing all LeapFinger objects attached to this hand.
Since 1.0

- (LeapFrame *) frame
frame

The LeapFrame associated with this Hand.

LeapFrame *owningFrame = hand.frame;


This property is a weak reference to the LeapFrame object so it is only valid during the lifetime of the LeapFrame object while the LeapFrame object is in the history buffer or while your application maintains its own reference.

Return
The associated LeapFrame object, if available; otherwise, an invalid LeapFrame object is returned.
Since 1.0

- (float) grabAngle
grabAngle

The angle between the fingers and the hand of a grab hand pose.

The angle is computed by looking at the angle between the direction of the 4 fingers and the direction of the hand. Thumb is not considered when computing the angle. The angle is 0 radian for an open hand, and reaches pi radians when the pose is a tight fist.

Return
The angle of a grab hand pose between 0 and pi radians (0 and 180 degrees).
Since 3.0

- (float) grabStrength
grabStrength

Deprecated.

Since
2.0

- (int32_t) id
id

A unique ID assigned to this LeapHand object, whose value remains the same across consecutive frames while the tracked hand remains visible.

If tracking is lost (for example, when a hand is occluded by another hand or when it is withdrawn from or reaches the edge of the Leap field of view), the Leap may assign a new ID when it detects the hand in a future frame.

int handId = hand.id;


Use the ID value with the [LeapFrame hand:] function to find this LeapHand object in future frames.

LeapHand *knownHand = [frame hand:handID];


Return
The ID of this hand.
Since 1.0

- (BOOL) isLeft
isLeft

Identifies whether this Hand is a left hand.

if(hand.isLeft)
{
//Do left handed things...
}


Return
True if the hand is a left hand.
Since 2.0

- (BOOL) isRight
isRight

Identifies whether this Hand is a right hand.

if(hand.isRight)
{
//Do right handed things...
}


Return
True if the hand is a right hand.
Since 2.0

- (BOOL) isValid
isValid

Reports whether this is a valid LeapHand object.

if(hand.isValid){
//Use the data...
}


Return
YES, if this LeapHand object contains valid tracking data.
Since 1.0

- (LeapVector *) palmNormal
palmNormal

The normal vector to the palm.

If your hand is flat, this vector will point downward, or “out” of the front surface of your palm.

The direction is expressed as a unit vector pointing in the same direction as the palm normal (that is, a vector orthogonal to the palm).

LeapVector *normal = hand.palmNormal;


Return
The LeapVector normal to the plane formed by the palm.
Since 1.0

- (LeapVector *) palmPosition
palmPosition

The center position of the palm in millimeters from the Leap origin.

LeapVector *position = hand.palmPosition;


Return
The LeapVector representing the coordinates of the palm position.
Since 1.0

- (LeapVector *) palmVelocity
palmVelocity

The rate of change of the palm position in millimeters/second.

LeapVector *speed = hand.palmVelocity;


Return
The LeapVector representing the coordinates of the palm velocity.
Since 1.0

- (float) palmWidth
palmWidth

The estimated width of the palm when the hand is in a flat position.

float averageWidth = hand.palmWidth;


Return
The width of the palm in millimeters
Since
2.0

- (float) pinchDistance
pinchDistance

The distance between the thumb and index finger of a pinch hand pose.

The distance is computed by looking at the shortest distance between the last 2 phalanges of the thumb and those of the index finger. This pinch measurement only takes thumb and index finger into account.

Return
The distance between the thumb and index finger of a pinch hand pose in millimeters.
Since 3.0

- (float) pinchStrength
pinchStrength

Deprecated.

Since
2.0

- (NSArray *) pointables
pointables

The list of LeapPointable objects (fingers) detected in this frame that are associated with this hand, given in arbitrary order.

NSArray *pointableList = hand.pointables;


The list will always contain 5 fingers even when some fingers are blocked from view and when the user is missing digits.

Return
An NSArray containing all LeapPointable objects associated with this hand.
Since 1.0

- (LeapVector *) sphereCenter
sphereCenter

The center of a sphere fit to the curvature of this hand.

LeapVector *spherePosition = hand.sphereCenter;


This sphere is placed roughly as if the hand were holding a ball.

Return
The LeapVector representing the center position of the sphere.
Since 1.0

The radius of a sphere fit to the curvature of this hand.

float diameter = 2 * hand.sphereRadius;


This sphere is placed roughly as if the hand were holding a ball. Thus the size of the sphere decreases as the fingers are curled into a fist.

Return
The radius of the sphere in millimeters.
Since 1.0

- (LeapVector *) stabilizedPalmPosition
stabilizedPalmPosition

The stabilized tip position of this Pointable.

LeapVector *stabilizedPosition = hand.stabilizedPalmPosition;


Smoothing and stabilization is performed in order to make this value more suitable for interaction with 2D content.

Return
A modified tip position of this Pointable object with some additional smoothing and stabilization applied.
Since 1.0

- (float) timeVisible
timeVisible

The duration of time this Hand has been visible to the Leap Motion Controller.

float handPersistence = hand.timeVisible;


Return
The duration (in seconds) that this Hand has been tracked.
Since 1.0

Public Static Functions

+ (LeapHand *) invalid

Returns an invalid LeapHand object.

LeapHand *badHand = LeapHand.invalid;


Return
The invalid LeapHand instance.
Since 1.0