Geometry for FaceLandmark vs Camera

[JpEncausse]

Hello, I love the parralax effect but I'm a little lost in your code.

I implemented this codepen describe from this topic but I don't think it's a good idea to move the cube. It's better to move the camera according to the FaceLandmark like you did.

But ... I'ml lost ... how to move the camera according to FaceMesh ?

[vivien000]

Hi @JpEncausse.

Thanks for your feedback. Beside the parallax effect, the code is mainly adapted from the first chapter of https://discoverthreejs.com/book/

The parallax effect is implemented through only two files:

• geometry.js
• Loop.js

In geometry.js, things are a bit messy because various options are available (cf. the README file). You can only focus on the parts corresponding to BLAZE = false and distanceMethod = 0, which are the default options.

The essential steps are the following:

• you get the predictions of the model

        predictions = await model.estimateFaces({
            input: ctx.getImageData(0, 0, width, height),
            predictIrises: (distanceMethod == 1),
            flipHorizontal: false
        });

• you keep only the facial landmark between the two eyes

            keypoints = predictions[0].scaledMesh;
            centerX = keypoints[168][0];
            centerY = keypoints[168][1];

• you compute the horizontal angle, the vertical angle and the distance (here, width, height, HFOV, VFOV are derived from the video stream and some constant values)

        return [Math.atan(2 * (centerX - width / 2) / width * Math.tan(HFOV / 2)),
            Math.atan(2 * (centerY - height / 2) / height * Math.tan(VFOV / 2)),
            d
        ]

• you derive from this the (x, y, z) coordinates of the observer (that you'll use for the camera)

        const result = await getLocation(context, width, height);
...
        const [angle1, angle2, distance] = result;
...
        let d = this.distance;
        const tan1 = -Math.tan(this.angle1);
        const tan2 = -Math.tan(this.angle2);
        const z = Math.sqrt(d * d / (1 + tan1 * tan1 + tan2 * tan2))
        const cameraPosition = [z * tan1, z * tan2, z];
        const fov = 180 / Math.PI * 2 * Math.atan(HALF_DIAGONAL / d);
        return [cameraPosition, fov];

In Loop.js, we just periodically update the parameters for the camera:

      const result = await this.faceTracker.getCameraParameters();
      if (result !== null) {
        const [cameraPosition, fov] = result;
        this.cameraPosition = cameraPosition;
        this.fov = fov;
        this.lastUpdate = Date.now();
      }

I hope this helps!