问题描述
我使用以下几行来旋转SCNNode:
I'm rotating a SCNNode using the following lines:
let rotate = SCNAction.rotateByAngle(CGFloat(M_PI), aroundAxis:SCNVector3Make(0, 1, 0), duration: NSTimeInterval(10.0))
let repeat = SCNAction.repeatActionForever(rotate)
node.runAction(repeat)
然后我在render方法中打印节点的eulerAngles.y:
and i print the eulerAngles.y of the node in the render method:
let rad = Double(node.eulerAngles.y)
var angleInDegrees = fmodf(360.0 + -Float(rad) * (180.0 / Float(M_PI)), 360.0)
println("eulerAngles.y rad:\(rad) degree:\(angleInDegrees)")
但是在旋转过程中，我得到了奇怪的值，如下所示:
but I get strange values during rotation like the following:
...
eulerAngles.y rad:-1.38788688182831 degree:79.5201
eulerAngles.y rad:-1.40567290782928 degree:80.5391
eulerAngles.y rad:-1.4227991104126 degree:81.5204
eulerAngles.y rad:-1.44030773639679 degree:82.5236
eulerAngles.y rad:-1.45790004730225 degree:83.5315
eulerAngles.y rad:-1.47438871860504 degree:84.4763
eulerAngles.y rad:-1.49130213260651 degree:85.4453
eulerAngles.y rad:1.57079637050629 degree:270.0
eulerAngles.y rad:1.57079637050629 degree:270.0
eulerAngles.y rad:1.57079637050629 degree:270.0
eulerAngles.y rad:1.57079637050629 degree:270.0
eulerAngles.y rad:1.57079637050629 degree:270.0
eulerAngles.y rad:1.57079637050629 degree:270.0
eulerAngles.y rad:1.57079637050629 degree:270.0
eulerAngles.y rad:1.57079637050629 degree:270.0
eulerAngles.y rad:-1.49359321594238 degree:85.5766
eulerAngles.y rad:-1.47716772556305 degree:84.6355
...
我不明白为什么要打印270.你能解释一下我还是另一种方式以获得正确的节点角度?
I don't understant why 270 is printed. Can you explain me or there another wayto get the correct angle of the node?
推荐答案
欧拉角就是这样工作的.他们有两个怪癖(我分别将x，y和z分别称为pitch，yaw和roll):
That's how Euler angles work. They have two quirks (I'll refer to x, y, and z as pitch, yaw, and roll respectively):
-
roll和yaw随着从0到π(180度)的逆时针旋转而增加，然后跳至-π(-180度)，并随着旋转完成一个圆而继续增加至0；但是pitch增大到π/2(90度)，然后减小到0，然后减小到-π/2(-90度)，然后增大到0.
rollandyawincrease with counterclockwise rotation from 0 to π (180 degrees) and then jump to -π (-180 degrees) and continue to increase to 0 as the rotation completes a circle; butpitchincreases to π/2 (90 degrees) and then decreases to 0, then decreases to -π/2 (-90 degrees) and increases to 0.
在某些方向上值变得不准确.特别地，当pitch为±90度时，roll和yaw变得不稳定.请参阅关于万向节锁的维基百科文章.
Values become inaccurate in certain orientations. In particular, when pitch is ±90 degrees, roll and yaw become erratic. See the wikipedia article on gimbal lock.
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