Align a node with its neighbor in SceneKit - swift

Question

Using Swift 5.5, iOS 14
Trying to create a simple 3D bar chart and I immediately find myself in trouble.
I wrote this code...
var virgin = true
for i in stride(from: 0, to: 6, by: 0.5) {
let rnd = CGFloat.random(in: 1.0...4.0)
let targetGeometry = SCNBox(width: 0.5,
height: rnd,
length: 0.5,
chamferRadius: 0.2)
targetGeometry.firstMaterial?.fillMode = .lines
targetGeometry.firstMaterial?.diffuse.contents = UIColor.blue
let box = SCNNode(geometry: targetGeometry)
box.simdPosition = SIMD3(x: 0, y: 0, z: 0)
coreNode.addChildNode(box)
}
This works well, but all the bars a centred around their centre. But how can I ask SceneKit to change the alignment?
Almost got this working with this code...
box.simdPosition = SIMD3(x: Float(i) - 3,
y: Float(rnd * 0.5),
z: 0)
But the result isn't right... I want/need the bar to grow from the base.
https://youtu.be/KJgvdBFBfyc
How can I make this grow from the base?
--Updated with working solution--
Tried Andy Jazz suggestion replacing simdposition with the following formulae.
box.simdPosition = SIMD3(x:box.simdPosition.x, y:0, z:0)
box.simdPivot.columns.3.y = box.boundingBox.max.y - Float(rnd * 0.5)
Worked well, to which I added some animation! Thanks Andy.
changer = changeling.sink(receiveValue: { [self] _ in
var rnds:[CGFloat] = []
for i in 0..<12 {
let rnd = CGFloat.random(in: 1.0...2.0)
let targetGeometry = SCNBox(width: 0.45, height: rnd, length: 0.45, chamferRadius: 0.01)
let newNode = SCNNode(geometry: targetGeometry)
sourceNodes[i].simdPivot.columns.3.y = newNode.boundingBox.min.y
sourceNodes[i].simdPosition = SIMD3(x: sourceNodes[i].simdPosition.x, y: 0, z: 0)
rnds.append(rnd)
}
for k in 0..<12 {
if virgin {
coreNode.addChildNode(sourceNodes[k])
}
let targetGeometry = SCNBox(width: 0.45, height: rnds[k], length: 0.45, chamferRadius: 0.01)
targetGeometry.firstMaterial?.fillMode = .lines
targetGeometry.firstMaterial?.diffuse.contents = UIColor.blue
let morpher = SCNMorpher()
morpher.targets = [targetGeometry]
sourceNodes[k].morpher = morpher
let animation = CABasicAnimation(keyPath: "morpher.weights[0]")
animation.toValue = 1.0
animation.repeatCount = 0.0
animation.duration = 1.0
animation.fillMode = .forwards
animation.isRemovedOnCompletion = false
sourceNodes[k].addAnimation(animation, forKey: nil)
}
virgin = false
})

Answer 1

You have to position a pivot point of each bar to its base:
boxNode.simdPivot.columns.3.y = someFloatNumber
To reposition a pivot to bar's base use bounding box property:
boxNode.simdPivot.columns.3.y += (boxNode.boundingBox.min.y as? simd_float1)!
After pivot's offset, reposition boxNode towards negative direction of Y-axis.
boxNode.position.y = 0