An FGS file is a figure settings file used by Fig, a modern optical metrology (science and technology of measurements with light) data-rendering program. It contains figure environment settings and display properties of a curve for measuring light, which includes line style, point style, line color, and width.

Fig renders data for visualization and presentation purposes. It is a part of a software package with UU, an image-processing program that features image processing tools, professional optical metrology data analysis, basic drawing functions, and rapid prototyping methods. The UU program is often used to open Fig to display figures in windows so curves and surfaces can be compared.