Converting a nested SCNNode position to a CGPoint in screen space

Question

I'm trying to convert the 3d position of a nested SCNNode in to an x, y (CGPoint) coordinate (for overlaying a view over the object).

My SCNNode structure looks like:

      +-----------+
      | Root node |
      +-----+-----+
            |
            |
       +----+---+
    +--+ Node A +--+
    |  +--------+  |
    |              |
    |              |
    |              |
+---+----+    +----+---+
| Node B |    | Node C |
+--------+    +--------+

I'd like to get the screen space 2d position of NodeB. I'm aware of the convertPosition: and projectPoint: methods but I don't think I'm using them correctly.

Any pointers?

Edit:

Currently trying something like this:

SCNVector3 rootPosition = [[[[self view3D] scene] rootNode] convertPosition:[nodeB position] fromNode:nodeB];
SCNVector3 projectedPoint = [[self view3D] projectPoint:rootPosition];
NSLog(@"x %f y %f z %f", projectedPoint.x, projectedPoint.y, projectedPoint.z);

The resulting x, y, z are way off (and sometimes negative, which doesn't make sense in screen space as the object is plainly in view).

Can you post what you've got so far? – wogsland Dec 04 '15 at 14:16 — wogsland, Dec 04 '15 at 14:16

score 2 · Accepted Answer · answered Dec 04 '15 at 21:54

2

NodeB's position is specified in terms of NodeA's coordinate system. So I believe you want

rootPosition = [rootNode convertPosition:nodeB.position fromNode:nodeA]

answered Dec 04 '15 at 21:54

Hal Mueller

7,019
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score 2 · Answer 2 · answered Feb 03 '19 at 17:55

2

On swift4:

nodeAchildPosition = scnScene.rootNode.convertPosition(nodeA.position, from: nodeAchild)

answered Feb 03 '19 at 17:55

Serhii Didanov

2,200
1
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Is this answer getting the position of nodeB, or nodeA? (It seems reversed from Hal Mueller's answer!) And is there some (any?) reason you can't just use nodeB.parent for the `from` parameter? – livingtech Sep 28 '20 at 21:00

Converting a nested SCNNode position to a CGPoint in screen space

2 Answers2