# Unigine::Plugins::LeapMotion::Arm Struct

Notice

This structure represents a forearm and has the following set of properties:

 witdh Width of the forearm, in meters. is_valid Indicates whether the arm contains valid tracking data (1). elbow_position Coordinates of the elbow position. wrist_position Coordinates of the wrist position. center Coordinates of the center of the forearm. direction Normalized direction in which the arm is pointing (from elbow to wrist). basis Orthonormal basis vectors for the arm bone as a Matrix. Basis vectors specify the orientation of the arm bone: X - Perpendicular to the longitudinal axis of the arm bone; exits the arm laterally through the sides of the wrist. Y (or up vector) - Perpendicular to the longitudinal axis of the arm bone; exits the top and bottom of the arm. Increases in the upward direction. Z - Aligned with the longitudinal axis of the arm bone. Increases toward the wrist. The bases provided for the right arm use the right-hand rule; those for the left arm use the left-hand rule. Thus, the positive direction of the x-basis is to the right for the right arm and to the left for the left arm. You can change from right-hand to left-hand rule by multiplying the z basis vector by -1. You can use the basis vectors for such purposes as measuring complex finger poses and skeletal animation. NoticeConverting the basis vectors directly into a quaternion representation is not mathematically valid. If you use quaternions, create them from the derived rotation matrix not directly from the bases.
Notice
All coordinates are relative to the origin of the Leap Motion coordinate system.
The Arm structure is declared as follows:
Source code (C++)
``````struct Arm
{
float width;
int is_valid;
Unigine::Math::vec3 direction;
Unigine::Math::vec3 elbow_position;
Unigine::Math::vec3 wrist_position;
Unigine::Math::vec3 center;
Unigine::Math::mat4 basis;
};``````

## floatgetWidth ( ) #

Returns the width of the forearm.

### Return value

Width of the forearm, in meters.

## vec3getElbowPosition ( ) #

Returns the coordinates of the elbow position.
Notice
All coordinates are relative to the origin of the Leap Motion coordinate system.

### Return value

Coordinates of the elbow position.

## vec3getWristPosition ( ) #

Returns the coordinates of the end of the bone, closest to the finger tip (distal).
Notice
All coordinates are relative to the origin of the Leap Motion coordinate system.

### Return value

Coordinates of the wrist position.

## vec3getCenter ( ) #

Returns the coordinates of the center of the forearm.
Notice
All coordinates are relative to the origin of the Leap Motion coordinate system.

### Return value

Coordinates of the center of the forearm.

## vec3getDirection ( ) #

Returns the normalized direction in which the arm is pointing (from elbow to wrist).
Notice
All coordinates are relative to the origin of the Leap Motion coordinate system.

### Return value

Normalized direction in which the arm is pointing (from elbow to wrist).

## vec3getBasis ( ) #

Returns the orthonormal basis vectors for the arm as a Matrix.

Basis vectors specify the orientation of the arm bone:

• X - Perpendicular to the longitudinal axis of the arm bone; exits the arm laterally through the sides of the wrist.
• Y (or up vector) - Perpendicular to the longitudinal axis of the arm bone; exits the top and bottom of the arm. Increases in the upward direction.
• Z - Aligned with the longitudinal axis of the arm bone. Increases toward the wrist.

The bases provided for the right arm use the right-hand rule; those for the left arm use the left-hand rule. Thus, the positive direction of the x-basis is to the right for the right arm and to the left for the left arm. You can change from right-hand to left-hand rule by multiplying the z basis vector by -1.

You can use the basis vectors for such purposes as measuring complex finger poses and skeletal animation.

Notice
Converting the basis vectors directly into a quaternion representation is not mathematically valid. If you use quaternions, create them from the derived rotation matrix not directly from the bases.

### Return value

Orthonormal basis vectors for the arm bone as a Matrix.
Last update: 2019-12-25