3FR to PLT Converter

PLT is a vector file format associated with HP-GL (Hewlett-Packard Graphics Language), a plotter control language introduced by Hewlett-Packard in 1977 with the HP-9872 pen plotter. PLT files contain a sequence of two-letter ASCII commands that instruct a pen plotter to move, draw lines, select pens, and render text — commands like PU (pen up), PD (pen down), PA (plot absolute), and SP (select pen) form a straightforward instruction set that directly controls physical drawing motion. The language operates on a coordinate grid measured in plotter units (typically 0.025 mm per unit), and the resulting files read almost like machine code for a drawing device. HP-GL became the dominant standard for computer-aided design output, adopted by virtually every CAD application and supported by plotters from all manufacturers throughout the 1980s and 1990s. One advantage is universal CAD compatibility — PLT files generated by AutoCAD, SolidWorks, or any engineering software can be sent directly to plotters and cutting machines without driver translation. The text-based, human-readable command structure is another strength: engineers can inspect, edit, and hand-write PLT files to troubleshoot output or generate simple drawings programmatically. HP-GL/2, an enhanced version introduced with the HP LaserJet III in 1990, added polygon fills, Bezier curves, and raster support. PLT remains actively used in engineering, architecture, and manufacturing for large-format output.