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Ultimate AutoCAD Lisp: Instantly Reverse Polyline Direction (REVPL)

ByCADAuthority Team

Program Description

The ReversePolyline.lsp (REVPL) tool is built for production work where object direction directly affects readability and standards compliance.

If you’ve ever had to:

  • flip linetype text in AutoCAD
  • fix upside down GAS or WATER lines
  • correct arrows pointing the wrong way

then you’re dealing with entity direction, not a linetype issue.

This routine solves it using AutoCAD’s native REVERSE command, which means:

  • No geometry rebuild
  • No risk of corrupting arcs or widths
  • Full compatibility with complex objects

Supported objects:

  • LINE
  • LWPOLYLINE
  • POLYLINE (2D & 3D)
  • SPLINE

Why Direction Matters in Real Projects

This is not a minor drafting detail. It affects deliverables and coordination.

  • Linetype text (GAS, STORM, WATER) reads backward if direction is wrong
  • Flow arrows misrepresent system behavior
  • Utility layouts become misleading
  • GIS exports may carry inconsistent topology

Redrawing elements is not realistic on large projects. You need a reliable batch tool.

The REVPL AutoLISP Code (Correct and Production-Ready)

Below is the correct version. Note the proper function definition:

;;; -------------------------------------------------------------------------
;;; ReversePolyline.lsp
;;; Command: REVPL
;;; Description: Reverses the direction of selected lines and polylines.
;;; -------------------------------------------------------------------------
(defun c:REVPL (/ ss)
  (vl-load-com)
  (prompt "\nSelect lines or polylines to reverse direction: ")
  (if (setq ss (ssget '((0 . "LINE,LWPOLYLINE,POLYLINE,SPLINE"))))
    (progn
      (vl-cmdf "_.REVERSE" ss "")
      (princ (strcat "\nSuccess: Reversed " (itoa (sslength ss)) " object(s)."))
    )
    (princ "\nNo valid objects selected.")
  )
  (princ)
)
(princ "\nReversePolyline.lsp loaded. Type REVPL to execute.")
(princ)

Critical Note

The command is defined as:

(defun c:REVPL …)

If the command name is missing (e.g., (defun c ...)), AutoCAD will not create the REVPL command and the routine will fail.

Step-by-Step Guide: How to Use REVPL

1. Save the File

Save the code as:

ReversePolyline.lsp

2. Load the LISP

  • Type APPLOAD
  • Load the file
  • Or drag and drop into AutoCAD

Official reference: https://help.autodesk.com/view/ACD/2024/ENU/?guid=GUID-APPLOAD

3. Run the Command

Type:

REVPL

Press Enter

4. Select Objects

  • Select single objects
  • Use window or crossing selection
  • Process entire networks if needed

5. Execute

Press Enter

AutoCAD will:

  • Reverse direction instantly
  • Display the result:

Success: Reversed X object(s).

Technical Advantages

Uses Native AutoCAD REVERSE Command

The routine calls:

_.REVERSE

Reference: https://help.autodesk.com/view/ACD/2024/ENU/?guid=GUID-REVERSE

This ensures:

  • Proper handling of arc bulges
  • Preservation of polyline widths
  • Full support for 3D polylines
  • Safe processing of splines

Avoids Common LISP Failures

Manual routines often:

  • Break arcs into segments
  • Lose width data
  • Fail on splines
  • Corrupt 3D geometry

This approach avoids all of that.

Batch Processing Ready

  • Works on selection sets
  • No manual iteration
  • Efficient on large drawings

Real-World Use Cases

Fix Linetype Text Direction

Search terms like:

  • AutoCAD flip linetype text
  • fix upside down gas line AutoCAD

This tool directly solves that issue without redefining linetypes.

Utility and Civil Drawings

  • Sewer systems
  • Storm networks
  • Gas and water lines

Ensures consistent direction across plans.

Survey and GIS Data Cleanup

Imported data often comes with inconsistent direction.

REVPL allows:

  • Fast correction
  • Clean deliverables
  • Reduced manual work

3D and Topographic Work

  • Maintains elevation data
  • Preserves vertex order
  • Safe for grading workflows

Integration Into Your Workflow

Recommended:

  • Add to Startup Suite (APPLOAD)
  • Store in a shared CAD support path
  • Assign a shortcut alias (e.g., RV)

Also useful in:

  • Tool palettes
  • Batch scripts
  • Standard CAD environments

Best Practices

  • Run after importing external files
  • Use before plotting when linetypes matter
  • Combine with:
    • OVERKILL
    • PEDIT JOIN

Keep direction consistent early to avoid rework.

Download and Use It Now

Download the script, load it once, and eliminate manual reversing from your workflow.

FAQ

What objects are supported?

LINE, LWPOLYLINE, POLYLINE (2D & 3D), SPLINE

Does it preserve arc segments?

Yes. Bulges remain intact because AutoCAD handles the reversal internally.

Can it process multiple objects?

Yes. It works on the full selection set.

Does it work on 3D polylines?

Yes. Z coordinates are preserved.

Will it damage geometry?

No. It uses AutoCAD’s native command, not custom reconstruction.

Can I undo the operation?

Yes. Use standard UNDO.

Does it affect linetype scale or properties?

No. Only direction is modified.

Is this the right tool for linetype text issues?

Yes. It directly solves:

  • AutoCAD flip linetype text
  • fix upside down gas line AutoCAD

Follow-up

Do you mainly need this for linetype text correction, or are you also working with 3D polylines in topo or grading models where direction consistency matters?

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