定义 SCNNode 的位置

Question

I create the SCNBox based on the SCNVector3 . But I don't understand the concept of the creation.

For 2D rectangle, the x and y represent the rectangle top right corner. For ARKit 3D SCNBox , what is the x, y and z represent for? Is that represent the center of the SCNBox ?

Answer 1

When you're setting position of your SCNNode , you're initializating SCNVector3 which describing node's position.

You have to define position of node's center point in relation to the position of the parent ( center point is not necessarily in the center of your custom node, but if you have basic nodes with geometry like SCNBox or SCNSphere , center point is in the center)

A simple example can be adding node with geometry SCNBox to rootNode of sceneView 's scene which you get when you in Xcode create new Augmented Reality App .

let cube = SCNBox(width: 0.1, height: 0.1, length: 0.1, chamferRadius: 0)
let material = SCNMaterial()
material.diffuse.contents = UIColor.red
cube.materials = [material]
let node = SCNNode()
node.position = SCNVector3(x: 0, y: 0, z: -0.5)
node.geometry = cube
sceneView.scene.rootNode.addChildNode(node)

As you can see, to initialize SCNVector3 you have to define x, y and z positions of node's center point . Note that units are in meters.

I created (very nice) picture with x,y and z axises which should help you to understand how to position your SCNNode :

...origin is origin of the node's parent's coordinate system when node is added. Image origin of AR world simplified as position of the center of ARSCNView