FACE2PLN-bgol (Convert 3DFACE to 3D 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 3DFACE-to-polyline conversion 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

F2PL converts a selected 3DFACE entity into an equivalent closed 3D polyline tracing the same vertices. AutoCAD's native AREA command cannot work directly on 3DFACE entities, converting to a 3D polyline unlocks area calculation and other polyline-based tools for triangulated surface data (a TIN of 3D faces).

How to Use

1. Load FACE2PLN-bgol.lsp into your CAD session (drag-and-drop the file onto the drawing window, or use the APPLOAD command).
2. Type F2PL at the command line and press Enter.
3. Select one or more 3DFACE entities.
4. Press Enter to finish the selection.
5. Each 3DFACE is rebuilt as a closed 3D polyline on a dedicated layer, BGOL-F2PL (colour magenta), tracing the exact same vertices. The original 3DFACE entities are left untouched.

Why Use It

• Unlocks AREA, AREA and similar tools work on 3D polylines but not on raw 3DFACE entities.
• True 3D surface area, enables computing true (sloped) surface area from a TIN, which is always greater than or equal to the flat 2D plan area.
• Geometry preserved exactly, same vertices, same shape; this is an entity-type conversion, not a geometric approximation.

Where to Use It

• Calculating true surface area of a triangulated survey surface (TIN) represented as 3D faces, earthworks, land grading, surface reporting.
• Any workflow needing to apply polyline-based tools (area, vertex export, coordinate tables) to geometry that currently exists only as 3DFACE entities.
• Preparing 3D-face surface data for further processing by other polyline-oriented routines.

Notes

• Handles both triangular and quadrilateral 3DFACE entities, if the 3rd/4th vertex coincide (a triangular face), the duplicate point is dropped automatically.
• The original 3DFACE entities are not deleted, so you can compare or remove them 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.