topic Re: Extract polylines from corridor featureline HAVE to be 3dpoly? in Civil 3D Forum

Extract polylines from corridor featureline HAVE to be 3dpoly?

RobertEVs — Fri, 29 May 2026 16:01:52 GMT

I often extract polylines from my corridor featureline then wind up with 3dplines which I have to convert 3d to 2d then flatten elevations. I use the plines for linework illustrations.

Is there any way to get flattened 2d plines from corridor featurelines in one shot?

Re: Extract polylines from corridor featureline HAVE to be 3dpoly?

SoaresASBCAD — Fri, 29 May 2026 16:31:26 GMT

Olá @RobertEVs

Yes. In Autodesk Civil 3D you can avoid the extra 3D Polyline → 2D Polyline → FLATTEN workflow by extracting the corridor featurelines differently.

A few options:

When using Extract Corridor Feature Lines, check whether you can extract them as Polylines instead of Feature Lines/3D Polylines (depends on version and settings).

Another reliable workflow is:

Extract the corridor featureline
Use Create Feature Line from Objects only if needed
Run MAPCLEAN or FLATTEN with Elevation = 0
Convert directly with CONVERT3DPOLYS

But the fastest “one-shot” method for drafting/illustration linework is usually:

Extract corridor featurelines
Use EXPORTTOAUTOCAD
During export, Civil 3D objects become plain AutoCAD entities and many featurelines simplify into standard 2D geometry depending on source elevations.

Another very efficient approach:

Set your UCS/View to Plan

Use FLATSHOT or create projected geometry from the corridor in plan view

This generates clean 2D linework specifically for presentation sheets and illustrations.

If you do this often, a small AutoLISP routine can automate:

extract featureline
convert 3D polyline
set all Z values to 0
output standard 2D polyline

That ends up being essentially a single command.

Re: Extract polylines from corridor featureline HAVE to be 3dpoly?

chriscowgill7373 — Fri, 29 May 2026 20:43:48 GMT

Sincpac might have the ability to extract 2d polylines. I dont have it in front of me to look. At my previous company, we just used the corridor for the linework. And my current company, corridors are only used for grading, and the roadway linework is drawn 2d from the start. I dont know which one is better, both workflows take a lot to update. The biggest issue with the corridors was that you couldnt snap to them to place a leader or dimension. At least not through an xref.

Looks like ti does 3d polylines, but then you could convert them.

https://info.quuxsoft.com/SincpacC3D_Help/SP_CorridorExtractPolylines.htm

Re: Extract polylines from corridor featureline HAVE to be 3dpoly?

RobertEVs — Fri, 29 May 2026 20:56:14 GMT

Thanks Christopher. Yes I have the Sincpac and you may be right I do know it has extract flattened 2d polyline command not sure if that is for corridor featurelines though. Not in front of it right now either.

The one you posted is kind of what I do already using C3D. I set my code set style to show certain featurelines I want to extract only, in my case bench_in for retaining walls. My problem is they come in as 3dplines and with elevation which I have to convert to 2D then flatten.

Re: Extract polylines from corridor featureline HAVE to be 3dpoly?

chriscowgill7373 — Fri, 29 May 2026 21:01:50 GMT

If you use Extract2D (on Sincpac2 in the panel next to the Pipe Elevation Editor) it will change the 3d to 2d and flatten it in one step. Plus you can set other settings (like a specific layer)

Shoot their support a feature request, ask for an option to extract 2d polylines at 0 elevation for the corridor. They might get it into a future release.

Re: Extract polylines from corridor featureline HAVE to be 3dpoly?

navya_gelli — Wed, 03 Jun 2026 10:09:13 GMT

Hi @RobertEVs ,

Did the info from @chriscowgill7373 help answer your question?

If you’re still needing more help, feel free to share an update here. The community will be happy to jump in with any next steps to help you get where you need to be.