/**
     * rotate around the Z-axis
     */
    rotateZ(degrees) {
        const radians = toRadians(degrees);
        const cos = Math.cos(radians);
        const sin = Math.sin(radians);

        const {x, y, z} = this;
        return new Vector(
            (x * cos) + (y * -sin),
            (x * sin) + (y * cos),
            z
        );
    }

    rotateZSelf(degrees) {
        const radians = toRadians(degrees);
        const cos = Math.cos(radians);
        const sin = Math.sin(radians);

        const {x, y} = this;
        this.x = (x * cos) + (y * -sin);
        this.y = (x * sin) + (y * cos);
    }