On behalf of Marc Leydecker, Aerosoft is pleased to offer you this comprehensive LIN File Line specification tutorial.

Intro 

Painted line files (.lin) define taxiway markings that can be draped over DSFs, although they could can be used for other purposes too. 

Painted line files are standard X-Plane 8/9 text files starting with a header and then commands. The # defines a comment. For a .lin file to be valid, it must contain a TEXTURE command, a SCALE command and an S_OFFSET command. 

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LINE_PAINT

Painted lines are defining polygons in the DSF file. The polygon may have windings - only lat and lon coordinates are needed. The polygon parameter is used to indicate a closed loop (1) or open chain (0). 

If two coordinates are provided (lon, lat) then the line is made of line segments. But if it is made of four coordinates (lon, lat, control lon, control lat) then it is interpreted as bezier curves.