Camera Transform from Unity to Three

[Olivier_VDB]

I am trying to transform a scene in Unity to the same in Three.js.
I tried several approaches and all the web articles I could find. One rotation is eluding me though.

Unity is Left Handed, ZXY order of rotation
Three is Right handed, XYZ

Those are my camera and objects:
this.camera = new THREE.PerspectiveCamera( 60, ratio, 512, 4096 ); //21.23931

        this.camera.position.set( 1735, 1968.4, -1191) ;
        const posR = new THREE.Vector3(1581, 1.0,551);
        const posG = new THREE.Vector3(1415.26, 1.0, 666.77);
        const posB = new THREE.Vector3(1540.04, 1.07, 846.82);

I am flipping the Y and Z axis

    this.camera.position.set( this.camera.position.x, this.camera.position.z, this.camera.position.y) ;
	mesh1.position.set( mesh1.position.x, mesh1.position.z, mesh1.position.y) ;
	mesh2.position.set( mesh2.position.x, mesh2.position.z, mesh2.position.y) ;
	mesh3.position.set( mesh3.position.x, mesh3.position.z, mesh3.position.y) ;

The rotation works well for X,Y axis.
Quaternion approach :

   let angleX = 45;
   let angleY = 0;
   let angleZ = 0; 
    var unityQuat = new THREE.Quaternion();
    var unityEuler = new THREE.Euler(THREE.MathUtils.degToRad(angleX), THREE.MathUtils.degToRad(angleY),THREE.MathUtils.degToRad(angleZ), 'ZXY' ); 
    unityQuat.setFromEuler(unityEuler);
    const UQuat = unityQuat;
    var q = new THREE.Quaternion( UQuat.x, -UQuat.z, -UQuat.y, UQuat.w );
    var v = new THREE.Euler();  
    v.setFromQuaternion( q );
    unityEuler = v;
    this.camera.setRotationFromEuler( unityEuler );

or Euler approach

        let cameraRot = [THREE.MathUtils.degToRad(90 - angleX),THREE.MathUtils.degToRad(-angleZ), THREE.MathUtils.degToRad(-angleY)]
        var unityEuler = new THREE.Euler( cameraRot[0], cameraRot[1], cameraRot[2], 'YZX' );

[Olivier_VDB]

with AngleY of 30, all is good

With AngleZ of 15, it does not work.

In Unity it rotate around Z first, then apply the X. Make sense.

In Three.js it rotate around the X first it seems.

In my quaternion implementation, I can only get the X rotation working without the -1 multiplication, which does not make sense to me.

Euler apporach makes more sense to me,
let cameraRot = [THREE.MathUtils.degToRad(90 - angleX),THREE.MathUtils.degToRad(-angleZ), THREE.MathUtils.degToRad(-angleY)]
var unityEuler = new THREE.Euler( cameraRot[0], cameraRot[1], cameraRot[2], ‘YZX’ );

But present the exact same defect.

I understand I could try to flip the matrices directly but this seems heavy lifting to do that at every frame.

[Olivier_VDB]

Instead of flipping Y & Z, I tried to negate Z.
It works now with:

       let cameraRot = [THREE.MathUtils.degToRad(-angleX),THREE.MathUtils.degToRad(-angleY), THREE.MathUtils.degToRad(angleZ)]
       var unityEuler = new THREE.Euler( cameraRot[0], cameraRot[1], cameraRot[2], 'YXZ' );
this.camera.setRotationFromEuler( unityEuler ); 
       this.camera.position.set( this.camera.position.x, this.camera.position.y, -this.camera.position.z) ;
mesh1.position.set( mesh1.position.x, mesh1.position.y, -mesh1.position.z) ;