DBLOFST-bgol (Offset Polylines on Both Sides)

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 double-sided polyline offset utilities used in civil/road layout 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

DBOF offsets every selected polyline on both sides simultaneously, using separately specified right-side and left-side distances. Built for the common residential/subdivision layout scenario where only centerlines exist and both road edges (or canal edges, or right-of-way boundaries) need to be generated from them in one pass.

How to Use

1. Load DBLOFST-bgol.lsp into your CAD session (drag-and-drop the file onto the drawing window, or use the APPLOAD command).
2. Type DBOF at the command line and press Enter.
3. Select all the polylines (e.g., road centerlines) that need to be offset on either side.
4. Enter the right-side distance, then the left-side distance (these can differ, allowing asymmetric offsets).
5. The routine offsets every selected polyline on both sides at once, producing two new offset polylines (one per side) for each original centerline, placed on a dedicated layer, BGOL-DBOF (colour yellow).

Why Use It

• Produces both the right and left offset lines for many centerlines in a single operation, rather than running OFFSET twice (once per side) for every individual polyline.
• Right/left distances can be specified independently, supporting asymmetric offsets (different road-edge widths, or one-sided setbacks) without needing separate commands.
• Major time saver in layout/subdivision design where dozens of road centerlines need consistent edge-line generation.

Where to Use It

• Generating road edge lines (curb lines, pavement edges) from centerlines in a residential or commercial layout/subdivision project.
• Any infrastructure design task needing consistent, batch double-sided offsetting of multiple centerlines or reference lines (canal edges from a canal centerline, right-of-way boundaries from an alignment).
• Speeding up layout plan preparation where many parallel offset lines are needed from a set of base centerlines.

Notes

• Right and left are resolved using the polyline's own VLA Offset method with positive/negative distances, so the sense stays consistent regardless of the direction the polyline was originally drawn.
• If an offset would collapse a segment to zero length (distance larger than the geometry allows), that individual offset is skipped rather than raising an error; other selected polylines are still processed.
• 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.