
Great, now we *can't* get the lines

...
It is hard to do it by looking in a photo though.
The best is to use a thick water glass from your own kitchen so as to better judge thicknesses. I have found out in the past that even if you hold the glass in your hands it is still hard to determine the inner surface of it ... and if you misjudge thicknesses at its bottom, the Maxwell "look" will not be the same as in your control photo.
What you can do is:
a. <Fill up> the glass to its rim with something that hardens in the refrigerator (I don't know ... maybe water and let it freeze ... or use butter) ... or just play-dough. Once it has the shape of the cavity take the ice out ... and this will give you the outline of the inner surface.
b. place the ice and the glass side by side and take a side view photo of both (at a large focal length to minimize perspective)
This will give you the outside outline and the inside outline with a fair amount of accuracy.
c. The two outlines can be used to model the glass.
Short of a poor man's digitizing ...