Las cortinas van desde esta esquina hasta esa esquina.

Question

I would think that because people hang curtains inside, it would be logical to use “rincón” instead of “esquina”.

Answer

Hola GennadyIndeed we generally use esquina to refer to an angle outside, in the street for example and rincón to refer to an indoor space created by corners, not just the joining point but the space created in that angle. However, when you are hanging, measuring curtains, as in this example, we often use the word esquina more than rincon, because even though it is an indoor space, we want the measurements from the "corner point", not the space created by the angles. We want the exact measurements from point to point. I hope this clarified it.Saludos