Unable to rotate an SCNNode in ARKit

Question

I'm trying to rotate an SCNNode on the y-axis so my node (an arrow) points in the right direction. I want to make a navigation app that uses ARKit; each arrow needs to point to the next location of the route I have received. The retrieval of the route works properly.

The nodes are added to the rootNode of the scene. At some point I traverse an array of nodes to position them in the scene and apply scaling to the node (based on the distance), which is all done correctly. However, when I apply rotation, this has no effect. The rotation is done by modifying the rotation property of the node:

directionNode.rotation = SCNVector4(x:0, y:1:, z:0, w:Float(bearing))

This does not have the desired effect. I also tried to use the runAction method, also no effect:

directionNode.runAction(SCNAction.rotateBy(x: 0, y: CGFloat(bearing), z: 0, duration: 0))

Here's the code that positions and scales the nodes.

for i in 0...(directionNodes.count - 1) {
    let directionNode = directionNodes[i]
    let translation = MatrixHelper.transformMatrix(for: matrix_identity_float4x4, originLocation: startingLocation, location: directionNode.location)
    let position = SCNVector3.positionFromTransform(translation)
    let distance = directionNode.location.distance(from: startingLocation)
    DispatchQueue.main.async {
        let scale = 100 / Float(distance)
        directionNode.scale = SCNVector3(x: scale, y: scale, z: scale)
        directionNode.anchor = ARAnchor(transform: translation)
        directionNode.position = position
        if (i < (self.directionNodes.count - 1)) {
            // Apply rotation to the arrow
            let successiveStepLocation = self.directionNodes[i + 1].location!
            let bearing = directionNode.location.bearingToLocationRadian(successiveStepLocation)
            // rotate
            directionNode.rotation = SCNVector4(x:0, y:1:, z:0, w:Float(bearing))
        }
    }
}

This is all wrapped in a SCNTransaction.

Can anyone tell me why the rotation of the node is not working? Any help is greatly appreciated.

[EDIT]: I forgot to mention that the 3D arrow object that I'm trying to rotate always points in the same direction. Even when I 'walk around' it the arrow always points (in my case) to the left. Maybe this helps solving my issue...

Answer 1

Many thanks for the answer, helped me a lot in understanding the different ways of rotation.

However, it turns out there was a constraint on the node like this:

let billboardConstraint = SCNBillboardConstraint()
billboardConstraint.freeAxes = SCNBillboardAxis.Y
constraints = [billboardConstraint]

Commenting this code made the rotation work properly. Pretty dumb...

According to the documentation a SCNBillboardConstraint makes the object's z-axis always point towards the pointOfView node. But I do not quite understand the freeAxes property here. The default type is all, so it never rotates with respect to the point of view. So if I only set the Y constraint type, I can only apply rotation on the X and Z axes? Or am I wrong here?

Answer 2

Update: I reckon the problem is in singleSided shader you're using. You see the invisible side of your model. Just enable doubleSided material for your geometry:

directionNode.geometry?.firstMaterial?.isDoubleSided = true

You need to use values expressed in Radians (effective range is -6.28 to +6.28).

It's important in what direction your object is rotated >> CW or CCW. You can't see the single-sided geometry (at a certain angle) at a positive angle of rotation +.pi.

It works this way:

myNode.rotation = SCNVector4(x: 0, y: -1, z: 0, w: (.pi * 3) / 2)

...and when you're using SCNAction, too (and don't forget to assign a duration):

let action = SCNAction.repeatForever(SCNAction.rotate(by: -.pi, 
                                                  around: SCNVector3(0,1,0), 
                                                duration: 1.75))
myNode.runAction(action)

...and when you're using SCNTransaction, too:

let previousTransform = myNode.transform
let rotate = SCNMatrix4MakeRotation(0, 1, 0, (-Float.pi/2))

SCNTransaction.begin()
SCNTransaction.animationDuration = 3.75
myNode.transform = SCNMatrix4Mult(rotate, previousTransform)
SCNTransaction.commit()