I am looking for the generalized formula how to find the solid angle for a closed curve in $R^3$ then to generalize it for $R^n$. Thanks for answers and papers or books references and links that are related to the subject.
I am trying to express the general formula of the projection area ($S$) on the unit sphere as shown in the picture above.
For example how to find the solid angle for the special case?
A curve defined :