an interesting problem from writings of Regiomontanus is one that asks where to stand for the best view of a painting on wall, if you stand too close, you distort the upper portion. if you stand too far from the painting, well you are too far back and cannot see all the details of the painting. The following diagram illustrates the problem situation.
the painting on the wall is represented by segment AB, and the eye height of the person viewing the painting is represented by point C . Line t is a horizontal line drawn through point C