将 ARFaceAnchor 从左手坐标系翻转到右手坐标系 [英] Flip ARFaceAnchor from left-handed to right-handed coordinate system

问题描述

通过打印 faceAnchor.transform.columns.3 进行一些测试后，深入研究:

<块引用>

正x方向指向观察者的右侧(即人脸自己的左侧)，正y方向指向上方(相对于人脸本身，而不是世界)，正z方向指向观察者的外侧面对(面向观众)

---

Sarasvati 给出了进行转型的建议:

 func faceAnchorPoseToRHS(_ mat: float4x4) ->浮动4x4 {让更正Pos = float4(x: mat.columns.3.x, y: mat.columns.3.y, z: -mat.columns.3.z, w: 1)让 quat = simd_quatf(mat)让 newQuat = simd_quatf(角度:-quat.angle，轴:float3(quat.axis.x，quat.axis.y，-quat.axis.z))var newPose = float4x4(newQuat)newPose.columns.3 = CorrectPos返回新姿势}

---

基于 Andy Fedoroff 的更新:

extension ViewController: ARSCNViewDelegate {func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {守卫让 faceAnchor = 锚定为?ARFaceAnchor else { return }currentFaceAnchor = faceAnchor如果 node.childNodes.isEmpty，让 contentNode = selectedContentController.renderer(renderer, nodeFor: faceAnchor) {node.addChildNode(contentNode)}selectedContentController.session = sceneView?.sessionselectedContentController.sceneView = 场景视图}///- 标签:ARFaceGeometryUpdatefunc renderer(_ renderer: SCNSceneRenderer, didUpdate node: SCNNode, for anchor: ARAnchor) {守卫锚== currentFaceAnchor，让 contentNode = selectedContentController.contentNode，contentNode.parent == 节点否则{返回}sceneView.session.currentFrame!.anchors.first!.transform打印(currentFaceAnchor！.transform.columns.3)selectedContentController.session = sceneView?.sessionselectedContentController.sceneView = 场景视图selectedContentController.renderer(renderer, didUpdate: contentNode, for: anchor)}}

---

但是，我打印了 faceAnchor.transform.columns.3 并使用 True Depth 相机获得了 z 底片.下面显示 x,y,z,w 轴:

关于如何更正 z 轴的任何建议?提前谢谢您

解决方案

首先，让我们看看默认矩阵值是什么.

身份矩阵

这是一个带有默认值的 Identity 4x4 矩阵.

如果您需要有关 4x4 矩阵 元素的更多信息，请阅读

正+cos(a):

 ┌ ┐|cos -sin 0 0 ||sin cos 0 0 ||0 0 1 0 ||0 0 0 1 |└ ┘

这是一个负 Z 旋转表达式 (CW).

负-cos(a):

 ┌ ┐|-cos -sin 0 0 ||sin-cos 0 0 ||0 0 1 0 ||0 0 0 1 |└ ┘

After some testings by printing faceAnchor.transform.columns.3, digging in SO: ARFaceAnchor have negative Z position? and Apple's documentation: ARFaceAnchor, I realized that the z axis is actually flipped and it is not the right-handed coordinate system as in the documentation. The ARFaceAnchor claims the coordinate:

the positive x direction points to the viewer’s right (that is, the face’s own left), the positive y direction points up (relative to the face itself, not to the world), and the positive z direction points outward from the face (toward the viewer)

---

Sarasvati has given a suggestion on doing the transformation:

    func faceAnchorPoseToRHS(_ mat: float4x4) -> float4x4 {
    let correctedPos = float4(x: mat.columns.3.x, y: mat.columns.3.y, z: -mat.columns.3.z, w: 1)

    let quat = simd_quatf(mat)
    let newQuat = simd_quatf(angle: -quat.angle, axis: float3(quat.axis.x, quat.axis.y, -quat.axis.z))
    var newPose = float4x4(newQuat)
    newPose.columns.3 = correctedPos

    return newPose
}

---

Updates based on Andy Fedoroff:

extension ViewController: ARSCNViewDelegate {
    func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
        guard let faceAnchor = anchor as? ARFaceAnchor else { return }
        currentFaceAnchor = faceAnchor
        if node.childNodes.isEmpty, let contentNode = selectedContentController.renderer(renderer, nodeFor: faceAnchor) {
            node.addChildNode(contentNode)
        }
        selectedContentController.session = sceneView?.session
        selectedContentController.sceneView = sceneView
    }
    /// - Tag: ARFaceGeometryUpdate
    func renderer(_ renderer: SCNSceneRenderer, didUpdate node: SCNNode, for anchor: ARAnchor) {
        guard anchor == currentFaceAnchor,
            let contentNode = selectedContentController.contentNode,
            contentNode.parent == node
            else { return }
        sceneView.session.currentFrame!.anchors.first!.transform
        print(currentFaceAnchor!.transform.columns.3)
        selectedContentController.session = sceneView?.session
        selectedContentController.sceneView = sceneView
        selectedContentController.renderer(renderer, didUpdate: contentNode, for: anchor)
    }
}

---

However, I printed faceAnchor.transform.columns.3 and obtained the z negative with True Depth camera. Below show x,y,z,w axis:

Any suggestions on how to correct the z-axis? Thank you in advance

解决方案

At first, let's see what a default matrix values are.

Identity matrix

Here's an Identity 4x4 matrix with default values.

If you need additional info on elements of 4x4 matrices read this post.

 // 0  1  2  3
 ┌              ┐
 |  1  0  0  0  |  x
 |  0  1  0  0  |  y
 |  0  0  1  0  |  z
 |  0  0  0  1  |
 └              ┘

Position Mirroring

To flip entity's Z axis and X axis, in order to reorient axis from Face tracking environment to World tracking environment, use the following form of 4x4 transform matrix.

 // 0  1  2  3
 ┌              ┐
 | -1  0  0  0  |  x
 |  0  1  0  0  |  y
 |  0  0 -1  0  |  z
 |  0  0  0  1  |
 └              ┘

Rotation Mirroring

In 4x4 transform matrices rotation is a combination of scale and skew. To choose a right rotation's direction, clockwise (CW) or counter-clockwise (CCW) use + or - for cos expressions.

Here's a positive Z rotation expression (CCW).

Positive +cos(a):

 ┌                    ┐
 | cos -sin   0    0  |
 | sin  cos   0    0  |
 |  0    0    1    0  |
 |  0    0    0    1  |
 └                    ┘

And here's a negative Z rotation expression (CW).

Negative -cos(a):

 ┌                    ┐
 |-cos -sin   0    0  |
 | sin -cos   0    0  |
 |  0    0    1    0  |
 |  0    0    0    1  |
 └                    ┘

这篇关于将 ARFaceAnchor 从左手坐标系翻转到右手坐标系的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！