Let $X$ be a smooth surface in $\mathbb{R}^{3}$. I want to compute the first fundamental form of $X$. Assume that $X$ has 2 different local parameterizations $r_1$, $r_2$ (i.e. for $r_1$ there is a $U_1 \subset X$ open and $V_1 \subset\mathbb{R}^{3}$ open such that $r_{1}: V_{1} \to U_{1}$ is a homeomorphism, $r_1$ is a smooth function and $\frac{d}{du}r_1(u,v)$ and $\frac{d}{dv}r_1(u,v)$ are linear independent. Analogously, we find $U_2 \subset X$ open and $V_2 \subset \mathbb{R}^{3}$ open, such that $r_2: V_{2} \to U_{2}$ satisfies the similar properties as $r_1: V_{1} \to U_{1}$. Moreover $U_{1} \cup U_{2}=X$.).
Assume there is a parameterization $f$ of $X$ in the general sense (i.e $f: U \to X$ surjective, where $U\subset \mathbb{R}^{3}$, but e.g. $f$ has not to be homeomorphism or has to satisfy other properties of the local parameterization above). Assume that $f$ is biijective.
Can I compute the first fundamental form with $f$ or do I have to compute a first fundamental form w.r.t. $r_1$ and $r_2$?