Get size of dae node

SCNBox is just helper subclass of SCNGeometry for box geometry creation. When you import Collada into a scene, you get scene graph of SCNNodes with SCNGeometries, not SCNBox'es or SCNCones etc doesn't matter how they look. If you want to get dimensions of any node you should use SCNBoundingVolume protocol, which is implemented by both SCNNode and SCNGeometry classes:

func getBoundingBoxMin(_ min: UnsafeMutablePointer, max max: UnsafeMutablePointer) -> Bool

With this method you will get bounding box corners. For box-shaped geometry, dimensions will match bounding box.

Example:

var v1 = SCNVector3(x:0, y:0, z:0)
var v2 = SCNVector3(x:0, y:0, z:0)
node.getBoundingBoxMin(&v1, max:&v2)

Where node is node you want to get bounding box of. Results will be in v1 and v2.

Swift 3

Using Swift 3 you can simply use node.boundingBox.min and node.boundingBox.max respectively.

Example Swift code on how to use boundingBox:

var min = shipNode.boundingBox.min
var max = shipNode.boundingBox.max
let w = CGFloat(max.x - min.x)
let h = CGFloat(max.y - min.y)
let l = CGFloat(max.z - min.z)
let boxShape = SCNBox (width: w , height: h , length: l, chamferRadius: 0.0)
let shape = SCNPhysicsShape(geometry: boxShape, options: nil)

shipNode.physicsBody!.physicsShape = SCNPhysicsShape(geometry: boxShape, options: nil)
shipNode.physicsBody = SCNPhysicsBody.dynamic()