XPTMARK-bgol (Find Intersections — Arc, Line, 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 intersection-marking 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

XPM finds every point where selected LINE, ARC and/or LWPOLYLINE entities intersect one another and marks each intersection point with a visible circle, including geometrically complex arc intersections, which are error-prone to determine manually.

How to Use

1. Load XPTMARK-bgol.lsp into your CAD session (drag-and-drop the file onto the drawing window, or use the APPLOAD command).
2. Type XPM at the command line and press Enter.
3. Select two or more LINE, ARC and/or LWPOLYLINE entities (any mix).
4. Press Enter to finish the selection.
5. Every intersection point found is marked with a small circle on a dedicated layer, BGOL-XPM (colour magenta). The selected entities are left untouched.

Why Use It

• Mixed entity types in one pass, handles lines, arcs and polylines together, removing the need for separate manual checks per entity type.
• Correct arc intersections, computed via the ActiveX IntersectWith method, avoiding manual/visual arc geometry errors.
• Immediately reviewable, clear visual markers appear right on the drawing instead of a separate text report to interpret.

Where to Use It

• Reviewing complex survey or design drawings with numerous crossing lines, arcs, and polylines.
• Identifying crossing points between features such as utility lines, road edges, or boundary segments that include curved sections.
• Any drafting QA or analysis task needing to programmatically identify all intersection points among a set of mixed-type linear entities.

Notes

• Intersection points are de-duplicated (within a small tolerance) before marking, so entities crossing at the same point are not marked twice.
• Marker circle radius defaults to 1.5 drawing units; edit the *bgol-xpm-radius* constant near the top of the .lsp file to change marker size.
• Uses vlax-invoke ... 'IntersectWith at the ActiveX object level, so line-line, line-arc, arc-arc, and polyline combinations are all handled automatically without separate formulas per entity-type pair.
• 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.