ARKit: Placing an SCNText at a particular point in front of the camera

Question

I've managed to get a cube (SCNNode) placed on a surface where the camera is pointed, however I am finding it very difficult to do the simple (?) task of also placing text in the same position.

I've created the SCNText and subsequent SCNNode, however when I add it to the rootNode the text always seems to be added above my head and off the camera to the right (which tells me thats the global origin point).

Even when I use the exact same values of position I used for the the cube, the SCNText node still gets placed above my head in the same spot.

Apologies if this is a basic question, I've never worked in SceneKit before.

Answer 1

The coordinate center for an SCNGeometry is its center point. But when you are creating a SCNText the center point is somewhere in the bottom left corner:

You need to center the text first. This can be done by checking the bounding box of the node containing your text and setting a pivot transform to change the texts center to its actual center:

func center(node: SCNNode) {
    let (min, max) = node.boundingBox

    let dx = min.x + 0.5 * (max.x - min.x)
    let dy = min.y + 0.5 * (max.y - min.y)
    let dz = min.z + 0.5 * (max.z - min.z)
    node.pivot = SCNMatrix4MakeTranslation(dx, dy, dz)
}

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Edit:

Also note this answer that explains some additional pitfalls: A text with 16 pts font size is 16 SceneKit units tall. But in ARKit 1 SceneKit units = 1 meter!