VXTHIN-bgol (Reduce Vertex Count by Distance Sampling)

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 vertex-reduction/curve-sampling 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

VXTH reduces vertex count on a dense polyline (e.g., a breakline digitized from LiDAR or detailed survey data) by rebuilding it from points sampled at a fixed distance interval along the original path. The result is a much lighter-weight polyline that still closely follows the original geometry.

How to Use

1. Load VXTHIN-bgol.lsp into your CAD session (drag-and-drop the file onto the drawing window, or use the APPLOAD command).
2. Type VXTH at the command line and press Enter.
3. Enter the sampling distance at which new vertices should be introduced (default 30 drawing units).
4. Select the polyline to reduce.
5. A new, lighter LWPOLYLINE is created on a dedicated layer, BGOL-VXTH (colour red). The command line reports the before/after vertex counts, e.g. No of Vertexes in Selected Line: 16 → No of Vertexes in Created Line: 5.

Why Use It

• Reduces drawing file size and improves CAD performance on drawings containing many vertex-heavy polylines.
• Preserves the overall shape/path of the original polyline reasonably well, since the new vertices are sampled directly from the original curve rather than arbitrarily simplified.
• Simple, predictable control via a single distance parameter, larger intervals produce fewer vertices (more aggressive reduction), smaller intervals preserve more detail.

Where to Use It

• Simplifying dense breaklines, contour-derived polylines, or LiDAR-sourced survey lines carrying far more vertices than the drawing needs.
• General drawing file-size and performance optimization on projects with many complex polylines.
• Preparing polylines for export to systems/formats with vertex count limits or performance sensitivity to complex geometry.

Notes

• The original polyline's actual endpoint is always included as the final point of the new line, even if it doesn't land exactly on a multiple of the sampling distance.
• Elevation/Z data is not preserved by this routine (2D sampling only); for 3D breaklines, verify the result before using it downstream.
• 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.