XSSMOOTH-bgol (Smooth Cross-Section Ground Line)

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 cross-section smoothing utilities used in survey/civil 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

Cross-section drawings built from straight-line segments connecting each measured value make the natural ground line look artificially angular rather than like a real, continuously undulating surface. Native CAD spline smoothing can deviate too far from the actual surveyed values to be usable. XSM smooths a cross-section ground line while staying much closer to the true data, controlled by a user-specified vertex insertion interval.

How to Use

1. Load XSSMOOTH-bgol.lsp into your CAD session (drag-and-drop the file onto the drawing window, or use the APPLOAD command).
2. Type XSM at the command line and press Enter.
3. Select the ground/natural-surface cross-section line to smooth.
4. Enter the vertex insertion interval (how densely new points should be sampled).
5. A new, smoothed LWPOLYLINE is created on a dedicated layer, BGOL-XSM (colour blue), closely tracking the original data. The source line is left completely untouched.

Why Use It

• Produces a much more realistic, natural-looking representation of ground surface in cross-section drawings compared to the raw straight-segment output most software generates.
• Avoids the major shape-deviation problem of native CAD spline smoothing, which can distort surveyed ground data to the point of being misleading.
• User control over the vertex insertion interval allows balancing smoothness against fidelity to the original data.
• Only the selected line is touched, other cross-section elements (design/canal profile, dimension text, etc.) remain sharp and accurate.

Where to Use It

• Improving the visual quality/realism of ground/natural-surface lines in cross-section drawings for canals, roads, drains, or any earthworks project.
• Client-facing or presentation-quality cross-section deliverables where a jagged, obviously-segmented ground line looks unprofessional or hard to interpret.
• Any cross-section drafting task needing a smoother ground representation while preserving reasonable adherence to surveyed values.

Notes

• Smoothing uses a simple 3-point moving average applied to the elevation (Y) component of each sampled point, not a full spline fit, which is what keeps the result close to the original data instead of overshooting like a native spline conversion can.
• The first and last points are left unsmoothed so the new line still starts and ends exactly where the original did.
• 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.