I am quite new and experimenting with Apple's ARKit and have a question regarding rotation information of the ARCamera. I am capturing photos and saving the current position, orientation and rotation of the camera with each image taken. The idea is to create 2d plane nodes with these images and have them appear in another view in the same position/orientation/rotation (with respect to the origin) as when when they were captured (as if the images were frozen in the air when they were captured). The position information seems to work fine, but the orientation/rotation comes up completely off as I’m having a difficulty in understanding when it’s relevant to use self.sceneView.session.currentFrame?.camera.eulerAngles vs self.sceneView.pointOfView?.orientation vs self.sceneView.pointOfView?.rotation.
This is how I set up my 2d image planes:
let imagePlane = SCNPlane(width: self.sceneView.bounds.width/6000, height: self.sceneView.bounds.height/6000)
imagePlane.firstMaterial?.diffuse.contents = self.image//<-- UIImage here
imagePlane.firstMaterial?.lightingModel = .constant
self.planeNode = SCNNode(geometry: imagePlane)
Then I set the self.planeNode.eulerAngles.x to the value I get from the view where the image is being captured using self.sceneView.session.currentFrame?.camera.eulerAngles.xfor x (and do the same for y and z as well).
I then set the rotation of the node as self.planeNode.rotation.x = self.rotX(where self.rotX is the information I get from self.sceneView.pointOfView?.rotation.x).
I have also tried to set it as follows:
let xAngle = SCNMatrix4MakeRotation(Float(self.rotX), 1, 0, 0);
let yAngle = SCNMatrix4MakeRotation(Float(self.rotY), 0, 1, 0);
let zAngle = SCNMatrix4MakeRotation(Float(self.rotZ), 0, 0, 1);
let rotationMatrix = SCNMatrix4Mult(SCNMatrix4Mult(xAngle, yAngle), zAngle);
self.planeNode.pivot = SCNMatrix4Mult(rotationMatrix, self.planeNode.transform);
The documentation states that eulerAngles is the “orientation” of the camera in roll, pitch and yaw values, but then what is self.sceneView.pointOfView?.orientation used for?
So when I specify the position, orientation and rotation of my plane nodes, is the information I get from eulerAngles enough to capture the correct orientation of the images?
Is my approach to this completely wrong or am I missing something obvious? Any help would be much appreciated!
If what you want to do is essentially create a billboard that is facing the camera at the time of capture then you can basically take the transform matrix of the camera (it already has the correct orientation) and just apply an inverse translation to it to move it to the objects location. They use that matric to position your billboard. This way you don't have to deal with any of the angles or worry about the correct order to composite the rotations. The translation is easy to do because all you need to do is subtract the object's location from the camera's location. One of the ARkit WWDC sessions actually has an example that sort of does this (it creates billboards at the camera's location). The only change you need to make is to translate the billboard away from the camer's position.
Related
I have 2 questions in mind to place 3D object.
If a 3D object(for example Car) created to face door side of the car as camera's front face, how can I rotate the 3D object to make it normal? Like, rotate the car to make engine side of a car as camera's front face.
2.How to place the 3D object on Plane Surface by facing the object towards the camera. Move the Phone camera to see the backside of the object.
I am using XCode 9.1 with iOS 11 and above, ARKIT
To rotate the car node you can just adjust the eulerAngles until the car is facing the camera.
node?.eulerAngles = SCNVector3Make(0,Float(degToRadians(degrees:180 )),Float(degToRadians(degrees: 90)))
rotated this van around to front facing.
eulerAngles are in radians, so a handy conversion to degrees:
public func degToRadians(degrees:Double) -> Double
{
return degrees * (M_PI / 180);
}
You can also do the same rotation on the van node using an animation
let rotate = SCNAction.rotateBy(x: CGFloat(degToRadians(degrees: -90)), y: 0, z: 0, duration: 1)
node.runAction(rotate)
You can use SCNLookAtConstraint which follows the pointOfView along the negative z-axis of the parentNode.
So if the car’s negative z-axis is the camera facing the side doors... as you rotate the camera, around the car.... the car will swivel always maintaining that view.
let constraint = SCNLookAtConstraint(target:sceneView.pointOfView)
constraint.isGimbalLockEnabled = true
node.constraints = [constraint]
Inside Xcode, the screenshot below shows how you can change the rotation of the van using the euler angles (highlighted in red). The view should be “front” camera (also highlighted in red). The animation can also be done inside Xcode via the animation panel, select “rotate Action” & drag into the Actions timeline in the bottom -middle
The graph is below:
ARFrame -> 3DModelFilter(SCNScene + SCNRender) -> OtherFilters -> GPUImageView.
Load 3D model:
NSError* error;
SCNScene* scene =[SCNScene sceneWithURL:url options:nil error:&error];
Render 3D model:
SCNRenderer* render = [SCNRenderer rendererWithContext:context options:nil];
render.scene = scene;
[render renderAtTime:0];
Now，I am puzzle on how to apply ARFrame's camera transform to the SCNScene.
Some guess:
Can I assign ARFrame camera's transform to the transform of camera node in scene without any complex operation?
The ARFrame camera's projectMatrix do not have any help to me in this case?
update 2017-12-23.
First of all, thank #rickster for your reply. According to your suggestion, I add code in ARSession didUpdateFrame callback:
ARCamera* camera = frame.camera;
SCNMatrix4 cameraMatrix = SCNMatrix4FromMat4(camera.transform);
cameraNode.transform = cameraMatrix;
matrix_float4x4 mat4 = [camera projectionMatrixForOrientation:UIInterfaceOrientationPortrait viewportSize:CGSizeMake(375, 667) zNear:0.001 zFar:1000];
camera.projectionTransform = SCNMatrix4FromMat4(mat4);
Run app.
1. I can't see the whole ship, only part of it. So I add a a translation to the camera's tranform. I add the code below and can see the whole ship.
cameraMatrix = SCNMatrix4Mult(cameraMatrix, SCNMatrix4MakeTranslation(0, 0, 15));
2. When I move the iPhone up or down, the tracking seem's work. But when I move the iPhone left or right, the ship is follow my movement until disappear in screen.
I think there is some important thing I missed.
ARCamera.transform tells you where the camera is in world space (and its orientation). You can assign this directly to the simdTransform property of the SCNNode holding your SCNCamera.
ARCamera.projectionMatrix tells you how the camera sees the world — essentially, what its field of view is. If you want content rendered by SceneKit to appear to inhabit the real world seen in the camera image, you'll need to set up SCNCamera with the information ARKit provides. Conveniently, you can bypass all the individual SCNCamera properties and set a projection matrix directly on the SCNCamera.projectionTransform property. Note that property is a SCNMatrix4, not a SIMD matrix_float4x4 as provided by ARKit, so you'll need to convert it:
scnCamera.projectionTransform = SCNMatrix4FromMat4(arCamera.projectionMatrix);
Note: Depending on how your view is set up, you may need to use ARCamera.projectionMatrixForOrientation:viewportSize:zNear:zFar: instead of ARCamera.projectionMatrix so you get a projection appropriate for your view's size and UI orientation.
I am currently trying to set up a rotating ball in scene kit. I have created the ball and applied a texture to it.
ballMaterial.diffuse.contents = UIImage(named: ballTexture)
ballMaterial.doubleSided = true
ballGeometry.materials = [ballMaterial]
The current ballTexture is a semi-transparent texture as I am hoping to see the back face roll around.
However I get some strange culling where only half of the back facing polygons are shown even though the doubleSided property is set to true.
Any help would be appreciated, thanks.
This happens because the effects of transparency are draw-order dependent. SceneKit doesn't know to draw the back-facing polygons of the sphere before the front-facing ones. (In fact, it can't really do that without reorganizing the vertex buffers on the GPU for every frame, which would be a huge drag on render performance.)
The vertex layout for an SCNSphere has it set up like the lat/long grid on a globe: the triangles render in order along the meridians from 0° to 360°, so depending on how the sphere is oriented with respect to the camera, some of the faces on the far side of the sphere will render before the nearer ones.
To fix this, you need to force the rendering order — either directly, or through the depth buffer. Here's one way to do that, using a separate material for the inside surface to illustrate the difference.
// add two balls, one a child of the other
let node = SCNNode(geometry: SCNSphere(radius: 1))
let node2 = SCNNode(geometry: SCNSphere(radius: 1))
scene.rootNode.addChildNode(node)
node.addChildNode(node2)
// cull back-facing polygons on the first ball
// so we only see the outside
let mat1 = node.geometry!.firstMaterial!
mat1.cullMode = .Back
mat1.transparent.contents = bwCheckers
// my "bwCheckers" uses black for transparent, white for opaque
mat1.transparencyMode = .RGBZero
// cull front-facing polygons on the second ball
// so we only see the inside
let mat2 = node2.geometry!.firstMaterial!
mat2.cullMode = .Front
mat2.diffuse.contents = rgCheckers
// sphere normals face outward, so to make the inside respond
// to lighting, we need to invert them
let shader = "_geometry.normal *= -1.0;"
mat2.shaderModifiers = [SCNShaderModifierEntryPointGeometry: shader]
(The shader modifier bit at the end isn't required — it just makes the inside material get diffuse shading. You could just as well use a material property that doesn't involve normals or lighting, like emission, depending on the look you want.)
You can also do this using a single node with a double-sided material by disabling writesToDepthBuffer, but that could also lead to undesirable interactions with the rest of your scene content — you might also need to mess with renderingOrder in that case.
macOS 10.13 and iOS 11 added SCNTransparencyMode.dualLayer which as far as I can tell doesn't even require setting isDoubleSided to true (the documentation doesn't provide any information at all). So a simple solution that's working for me would be:
ballMaterial.diffuse.contents = UIImage(named: ballTexture)
ballMaterial.transparencyMode = .dualLayer
ballGeometry.materials = [ballMaterial]
So I have a bit of a project I am trying to do. I am trying to get the devices rotation relative to gravity, and translation from where it started. So basically getting "tracking" data for the device. I plan to basically apply this by making a 3d pt that will mimic the data I record from the device later on.
Anyway to attempt to achieve this I thought it would be best to work with scene kit that way I can see things in 3 dimensions just like the data I am trying to record. Right now I have been trying to get the ship to rotate so that it always looks like its following gravity (like its on the ground or something) no mater what the device rotation is. I figure once I have this down it will be a sinch to apply this to a point. So I made the following code:
if let attitude = motionManager.deviceMotion?.attitude {
print(attitude)
ship.eulerAngles.y = -Float(attitude.roll)
ship.eulerAngles.z = -Float(attitude.yaw)
ship.eulerAngles.x = -Float(attitude.pitch)
}
When you only run one of the rotation lines then everything is perfectly. It does behave properly on that axis. However when I do all three axis' at once it becomes chaotic and performs far from expected with jitter and everything.
I guess my question is:
Does anyone know how to fix my code above so that the ship properly stays "upright" no matter what the orientation.
J.Doe!
First there is a slight trick. If you want to use the iphone laying down as the default position you have to notice that the axis used on sceneKit are different then those used by the DeviceMotion. Check the axis:
(source: apple.com)
First thing you need to set is the camera position. When you start a SceneKit project it creates your camera in the position (0, 0, 15). There is a problem with that:
The values of eulerAngles = (0,0,0) would mean the object would be in the plane xz, but as long as you are looking from Z, you just see it from the side. For that to be equivalent to the iphone laying down, you would need to set the camera to look from above. So it would be like you were looking at it from the phone (like a camera, idk)
// create and add a camera to the scene
let cameraNode = SCNNode()
cameraNode.camera = SCNCamera()
scene.rootNode.addChildNode(cameraNode)
// place the camera
cameraNode.position = SCNVector3(x: 0, y: 15, z: 0)
// but then you need to make the cameraNode face the ship (the origin of the axis), rotating it
cameraNode.eulerAngles.x = -Float(M_PI)*0.5 //or Float(M_PI)*1.5
With this we are going to see the ship from above, so the first part is done.
Now we gotta make the ship remain "still" (facing the ground) with the device rotation.
//First we need to use SCNRendererDelegate
class GameViewController : UIViewController SCNSceneRendererDelegate{
private let motion = CMMotionManager();
...
Then on viewDidLoad:
//important if you remove the sceneKit initial action from the ship.
//The scene would be static, and static scenes do not trigger the renderer update, setting the playing property to true forces that:
scnView.playing = true;
if(motion.deviceMotionAvailable){
motion.startDeviceMotionUpdates();
motion.deviceMotionUpdateInterval = 1.0/60.0;
}
Then we go to the update method
Look at the axis: the axis Y and Z are "switched" if you compare the sceneKit axis and the deviceMotion axis. Z is up on the phone, while is to the side on the scene, and Y is up on the scene, while to the side on the phone. So the pitch, roll and yaw, respectively associated to the X, Y and Z axis, will be applied as pitch, yaw and roll.
Notice I've put the roll value positive, that's because there is something else "switched". It's kinda hard to visualize. See the Y axis of device motion is correlated to the Z axis of the scene. Now imagine an object rotation along this axis, in the same direction (clock-wise for example), they would be going in opposite directions because of the disposition of the axis. (you can set the roll negative too see how it goes wrong)
func renderer(renderer: SCNSceneRenderer, updateAtTime time: NSTimeInterval) {
if let rot = motion.deviceMotion?.attitude{
print("\(rot.pitch) \(rot.roll) \(rot.yaw)")
ship.eulerAngles.x = -Float(rot.pitch);
ship.eulerAngles.y = -Float(rot.yaw);
ship.eulerAngles.z = Float(rot.roll);
}
Hope that helps! See ya!
Okay, this is driving me crazy. I've looked through tons of examples and can't seem to get quite what I need. I'm using XNA and I have a plane of vertices and my camera is up in the sky looking down on the vertices.
What I want is to rotate the camera around on the Y axis, basically get the same result as adjusting its YAW. However whenever I try to rotate around on the Y axis or adjust its YAW nothing actually happens. I can however get the effect I want by creating a Y rotation matrix on the world, but that doesn't feel like the "correct" way of doing it, I want the camera itself to spin and not the world. Here's a code snippet for what I have:
cameraPosition = Vector3.Transform(new Vector3(
cameraOffset.X - cameraOffset.X,
zoomAmount,
cameraOffset.Z - cameraOffset.Z),
Matrix.CreateRotationY(rotationAngle)) + cameraOffset;
view = Matrix.CreateLookAt(cameraPosition, cameraTarget, new Vector3(0, 0, 1));
Thanks!
Since you have the camera looking straight down, it sounds like what you want is for the camera to roll in local space. To roll your camera, you must rotate the Up vector you are feeding to the CreateLookAt(). Like this:
Vector3 newUp = Vector3.Transform(Vector3.UnitZ, Matrix.CreateRotationY(rotationAngle));
view = Matrix.CreateLookAt(cameraPosition, cameraTarget, newUp);