SCNNode Z旋转轴保持不变，而X和Y轴在节点旋转时发生变化 [英] SCNNode Z-rotation axis stays constant, while X and Y axes change when node is rotated

问题描述

我有一个用户可以通过平移手势旋转的节点.用户可以选择X，Y或Z轴并进行平移，节点将围绕该轴旋转.

I have a node that the user can rotate via a pan gesture. The user can select either X, Y, or Z axis and pan, and the node will rotate around that axis.

问题:节点的正面朝向摄像机.假设用户向右平移并围绕Y轴旋转节点.节点的正面现在朝向右侧.如果用户切换到X轴并向下平移，则节点的前部将从其初始的面向右方向向下旋转(或从用户的角度来看为顺时针方向).这是期望的行为.当用户切换到Z旋转时会出现问题.如果用户切换到Z轴旋转并向右平移，则该节点将向下旋转(从用户角度来看为顺时针方向).

The Issue: The node's front is facing the camera. Let's say the user pans to the right and rotates the node around the Y axis. The node's front is now facing the right. If the user switches to the X axis and pans down, the node's front will rotate downward (or clockwise from the user's perspective) from it's initial right-facing orientation. This is desired behavior. The problem arises when the user switches to the Z rotation. If the user switches to Z axis rotation and pans right, the node will rotate down (clockwise from the user's perspective).

从本质上讲，节点的Z轴始终是恒定的，永远不会偏离其初始方向，但是X轴和Y轴的确会发生变化，受其他轴的旋转的影响.

Essentially, the Z axis of the node is always constant, never moving from it's initial orientation, but the X and Y axes do change, affected by other axes' rotations.

任何人都可以解释是什么原因造成的吗?

Can anyone explain what's causing this?

下面是我用来旋转节点的代码:

Below is the code I'm using to rotate the node:

let translation = sender.translation(in: sceneView)
        var newAngleX = Float(translation.y)*Float((Double.pi)/180.0)
        var newAngleY = Float(translation.x)*Float((Double.pi)/180.0)
        var newAngleZ = Float(translation.x)*Float((Double.pi)/180.0)

        if axisSelected == "x" {
            newAngleX += currentAngleX
            node.eulerAngles.x = newAngleX
            if(sender.state == .ended) {
                currentAngleX = newAngleX
            }
        }
        if axisSelected == "y" {
            newAngleY += currentAngleY
            node.eulerAngles.y = newAngleY
            if(sender.state == .ended) {
                currentAngleY = newAngleY
            }
        }
        if axisSelected == "z" {
            newAngleZ += currentAngleZ
            node.eulerAngles.z = newAngleZ
            if(sender.state == .ended) {
                currentAngleZ = newAngleZ
            }
        }

推荐答案

正如我之前在

As I wrote earlier in your post it's a Gimbal Lock issue. Gimbal Lock is the loss of one DoF in a three-dimensional mechanism. There are two variables in SceneKit: eulerAngles (intrinsic euler angles, expressed in radians, represent a sequence of 3 rotations about the x-y-z axis with the following order: Z-Y-X or roll, yaw, pitch) and orientation (node’s orientation, expressed as quaternion).

要摆脱ARKit和SceneKit中的万向节锁定，您需要使用单元四元数，其四元数满足以下方程式:

To get rid of gimbal lock in ARKit and SceneKit you need to use unit quaternions, whose components satisfy the equation:

(x * x) + (y * y) + (z * z) + (w * w) == 1

要正确应用四元数，您还需要使用此结构的第四个组件(w).四元数用SCNVector4表示，其中x-y-z值是归一化的分量，w字段包含以弧度为单位的旋转角度或以牛顿米为单位的扭矩大小.

For applying quaternions correctly you need to use the fourth component of this structure too (w). Quaternions are expressed in SCNVector4, where x-y-z values are normalized components, and the w field contains the rotation angle, in radians, or torque magnitude, in newton-meters).

万向节锁定在将(三个万向节中的两个)轴驱动为平行配置时发生.

Gimbal Lock occurs when the axes (of two of the three gimbals) are driven into a parallel configuration.

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