SPL2SEG-bgol (Convert Smooth Polyline to Regular Polyline)

Command Type: AutoLISP routine (works in AutoCAD, BricsCAD, ZWCAD and most AutoLISP-compatible CAD platforms)
Developed by: BGol Community, bgol.in

Inspired by the general concept of spline-to-polyline resampling utilities used in CAD/survey drafting. This is an original, independently written routine, new file name, new command name, new source code, created so the CAD community has a free, editable, open-source alternative.

Overview

SP2P converts a smoothed (PEDIT → Spline) polyline back into a regular polyline built from many closely-spaced straight segments that trace the smooth curve's true shape. AutoCAD's spline-fit smoothing is purely cosmetic, many LISP tools still only see the original coarse vertices. This routine bridges that gap.

How to Use

1. Load SPL2SEG-bgol.lsp into your CAD session (drag-and-drop the file onto the drawing window, or use the APPLOAD command).
2. Type SP2P at the command line and press Enter.
3. Select the smoothed (splined) LWPOLYLINE.
4. A new, densely-segmented regular polyline that closely traces the original smooth curve is created on a dedicated layer, BGOL-SP2P (colour cyan). The original smooth polyline is left untouched.

Why Use It

• Bridges cosmetic vs. real geometry, spline-fit smoothing is visual only; this produces a polyline other LISP routines can process correctly.
• Keeps the smooth look, the dense segment spacing still appears visually smooth at normal zoom levels.
• Prep step, useful before running any other vertex-dependent routine (coordinate export, vertex marking, interpolation) on a polyline that was originally smoothed for presentation.

Where to Use It

• Converting aesthetically smoothed survey or design lines back into a computationally usable, densely-segmented polyline.
• Preparing curve-heavy drawings for export or analysis tools that require actual polyline vertex data rather than a spline definition.
• Any workflow where a polyline was smoothed for visual presentation but now needs vertex-based processing.

Notes

• Sampling density defaults to 60 points along the curve; edit the *bgol-sp2p-samples* constant near the top of the .lsp file for a finer or coarser result.
• Works on LWPOLYLINE entities; both open and closed smoothed polylines are supported.
• The original smoothed polyline is not deleted, so you can compare or remove it manually once you have confirmed the conversion.
• Source code is fully open, feel free to study, modify, and redistribute it under the same open, free-for-all spirit.

Credits

Developed and shared for the CAD community by BGol Community. Website: https://bgol.in/ Free and open-source, use it, modify it, share it, for personal or commercial work alike.