What methodology to follow to find coordinates on a curved surface?

I have a trouble on finding the "coordinates on a curved surface" when I take a picture of it. Imagine a barrel or a curved surface, having n points on its surface and we need to determine their location. When the surface is photographed from '"front" and about 30 degrees rotated, the relative position of the points will look different.

If it was a flat plate, I would think to normalize the lengths and find the relative coordinate of each point. Since it is a flat plate, each of the normalized coordinates would give the same number independent of the rotation angle. But when it is on a curved surface, that normalization does not help to find the coordinates. Is there a methodology to follow to be able to find the coordinates when the object is rotated?

A visual of an example problem could be seen here: https://imgur.com/nfHo8jR

A top view of another example figure could be seen, maybe easier to understand the change of point positions with rotation: https://imgur.com/JYOUyJp

[darova]

So if just scale y coordinate:

y = y/sind(30);    % or cosd(30). Depends where the angle is