Identify the start/end of the x and y axis of graph

[Derek-Jones]

A graph will contain at least one x and y axis (assume one of each to start).

The most likely start/end of the x and y axis needs to be identified.

Identify the two longest lines at right-angles to each other, is one possible heuristic.

pdf operations use page relative coordinates. Knowing the page relative coordinates allows the page relative coordinates of graph points to be mapped to graph relative coordinates.