Question

我试图在ARFaceAnchor中找到关于y轴的头部角度。我的开始示例是Apple的示例代码：creating face-based AR experiences。

鉴于此图像，我基本上搜索绿色标记（来自coordinateOrigin节点）相对于垂直轴的角度。

ARFaceAnchor对象继承自ARAnchor , providing a transform`属性：

编码锚点的位置，方向和比例的矩阵相对于锚点所在的AR会话的世界坐标空间放在。

此类transform的类型如下： var transform: matrix_float4x4 { get }

如何导出角度信息，例如从此矩阵中描述的角度信息？

Answer 1

由于 Apple 没有为此类提供四元数到欧拉的转换，就我而言，我必须手动计算它们，如下所示。

请找到参考 here，其灵感来自 this mathematical resource。

extension matrix_float4x4 {
   // Function to convert rad to deg
   func radiansToDegress(radians: Float32) -> Float32 {
       return radians * 180 / (Float32.pi)
   }
   var translation: SCNVector3 {
      get {
          return SCNVector3Make(columns.3.x, columns.3.y, columns.3.z)
      }
   }
   // Retrieve euler angles from a quaternion matrix
   var eulerAngles: SCNVector3 {
       get {
           // Get quaternions
           // http://www.euclideanspace.com/maths/geometry/rotations/conversions/matrixToQuaternion/index.htm
           let qw = sqrt(1 + self.columns.0.x + self.columns.1.y + self.columns.2.z) / 2.0
           let qx = (self.columns.2.y - self.columns.1.z) / (qw * 4.0)
           let qy = (self.columns.0.z - self.columns.2.x) / (qw * 4.0)
           let qz = (self.columns.1.x - self.columns.0.y) / (qw * 4.0)

           // Deduce euler angles with some cosines
           // https://en.wikipedia.org/wiki/Conversion_between_quaternions_and_Euler_angles
           /// yaw (z-axis rotation)
           let siny = +2.0 * (qw * qz + qx * qy)
           let cosy = +1.0 - 2.0 * (qy * qy + qz * qz)
           let yaw = radiansToDegress(radians:atan2(siny, cosy))
           // pitch (y-axis rotation)
           let sinp = +2.0 * (qw * qy - qz * qx)
           var pitch: Float
           if abs(sinp) >= 1 {
               pitch = radiansToDegress(radians:copysign(Float.pi / 2, sinp))
           } else {
               pitch = radiansToDegress(radians:asin(sinp))
           }
           /// roll (x-axis rotation)
           let sinr = +2.0 * (qw * qx + qy * qz)
           let cosr = +1.0 - 2.0 * (qx * qx + qy * qy)
           let roll = radiansToDegress(radians:atan2(sinr, cosr))
           
           /// return array containing ypr values
           return SCNVector3(yaw, pitch, roll)
           }
   }
}

在ARFaceTracking会话中找到ARFaceAnchor的头部倾斜角度

1 个答案: