fixed positions for three.js objects after scanning image

Expo SDK
1

Hey! I’m new to three.js and I try to create a 3D scene after scanning an image using ARKit with Expo on iOS.

The application recognizes the image and should place an 3d-object in to the images local coordinate system. This should be a fiexed position. My problem is, that the local coordinate system of the image always changes, so the 3d-object doesn’t get a fixed position.

Here is some code:

createScene = (name) => {



    //local coordinates based on office sign
    let x_local = this[name].position.x;
    let y_local = this[name].position.y;
    let z_local = this[name].position.z;


    console.log("local coords ", this[name].position)

    //3D Model to represent a chair 
    const chairGeometry = new THREE.BoxGeometry(0.3, 0.3, 0.3);
    const chairMaterial = new THREE.MeshBasicMaterial({ color: 0x00ff00 });


    const chair = new THREE.Mesh(chairGeometry, chairMaterial);


    //TODO: coordinate system with origin on detected object        

   switch (name) {
        case "office_sign_6c03":
            console.log("detected office_sign_6c03")

            break;
        case "office_sign_6c04":

            console.log("detected office_sign_6c04")
            chair.position.set(x_local + 3, y_local + 0,z_local -2)

            this.scene.add(chair)

            console.log("chair posi ", chair.position)

            break;

        default:
            break;
    }
    this.scene.add(chair)
}

Maybe I don’t get the meaning of the positions (of the image or of the camera) correctly. Can anybody help?

2

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