Camera position in orthographic projection

Question

I'm trying to understand how to use camera with usesOrthographicProjection = true. I need to set it up so when we first see the scene, the object should be viewable in full.

I used the Xcode's SceneKit template, adjust a little bit about the camera (all the code is in viewDidLoad). Using default camera (perspective projection), it looks like this:

cameraNode.position = SCNVector3(x: 0, y: 0, z: ship.boundingBox.max.z + 20)

Next, I tried to set the orthographic projection, now it looks like this:

cameraNode.camera?.usesOrthographicProjection = true
cameraNode.position = SCNVector3(x: 0, y: 0, z: ship.boundingBox.max.z + 20)

No matter how I tried to change the camera position, it still looks the same as the image above. I've tried using GLKMatrix4MakeOrtho to no avail. Nothing works. What should I do the change the first view impression?

cameraNode.camera?.usesOrthographicProjection = true

//    let width = Float(UIScreen.main.bounds.size.width)
//    let width: Float = 9
//    let glMat = GLKMatrix4MakeOrtho(-width/2, 
//                                    width/2, 
//                                    -width/2, 
//                                    width/2, 
//                                    1, 
//                                    1000)

//    let glMat = GLKMatrix4MakeOrtho(ship.boundingBox.min.x,
//                                    ship.boundingBox.max.x,
//                                    ship.boundingBox.min.y,
//                                    ship.boundingBox.max.y,
//                                    ship.boundingBox.min.z,
//                                    ship.boundingBox.max.z)
//    cameraNode.camera?.projectionTransform = SCNMatrix4FromGLKMatrix4(glMat)

cameraNode.position = SCNVector3(x: 0, 
                                 y: 0, 
                                 z: ship.boundingBox.max.z + 20)

have you tried `orthographicScale` ? read here - https://developer.apple.com/documentation/scenekit/scncamera/1436621-usesorthographicprojection — Blind Ninja, Dec 30 '20 at 07:29
@BlindNinja thanks, it seems setting `orthographicScale` works. However I have no clue how it works, since the document is not detailed. I'll try working on it for more results. — Eddie, Dec 30 '20 at 07:38
I am not 100% sure but it work like focal length. you were only setting it's position but how much area it should cover, that was unknown. You see same sized and positioned wide angle lens will have different projection than normal lens. — Blind Ninja, Dec 30 '20 at 07:46
okay, since `orthographicScale` works, I'm still not able to fully control the camera position. Like, I'd like to set the camera position at a little higher above and to the right (first view diagonal), it's not as I expected. Helps still needed. — Eddie, Dec 30 '20 at 09:50

Andy Jazz · Accepted Answer · 2020-12-30T10:48:56.937

Use orthographicScale instance property to control camera’s magnification factor when using an orthographic projection.

var orthographicScale: Double { get set }

Here's full code version:

import SceneKit

class GameViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let sceneView = self.view as! SCNView
        sceneView.scene = SCNScene(named: "art.scnassets/ship.scn")!
        sceneView.allowsCameraControl = true
        sceneView.backgroundColor = UIColor.black
        
        sceneView.pointOfView?.camera!.usesOrthographicProjection = true
        sceneView.pointOfView?.camera!.zNear = 0.1
        sceneView.pointOfView?.camera!.zFar = 50.0
        sceneView.pointOfView?.camera!.orthographicScale = 5.0
    }
}

Orthographic projection is a means of representing three-dimensional objects in two dimensions. So there's no distance in Z since we are in two dimensions. That's why you have to use an orthographicScale property. No matter how you move the camera with parallel projection beams, the distance to objects will remain unchanged.

So, take into consideration: in an orthographic projection, equally sized objects appear equally sized regardless of their distance from the camera.

The only parameter that controls a "distance" in two-dimensional space (there's no Z position in reality in 2D) is an orthographicScale.

still couldn't control the camera's position properly. Example, I'd like to set the camera at the position the at a little right upper (x = 2, y = 10) to the ship, then use `SCNLookAtConstraint` to constantly looking at the ship. I don't understand how the camera's position works when using orthographic. — Eddie, Dec 30 '20 at 10:18

Camera position in orthographic projection

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