Line Graphics Link File Format.
This file contains information about the inter-entity links. The line header file defines the number of data points in this file.
The file must contain mlink rows and four columns. The precise format of each piece of data is not critical, but the ordering of the columns is critical. The file format is as follows.
x11 y11 x12 y12 x21 y21 x22 y22 x31 y31 x32 y32 ...