If you have ever opened an older survey or grading drawing in Civil 3D and found contour lines that cannot be edited natively, you have met the AEC_Contour — a custom object left over from Autodesk Land Desktop. The usual advice online is "just explode them," which flattens the data, scatters the geometry into countless tiny segments, and often destroys the elevation you actually need.
DeAEC was built to do this properly. It reads each AEC contour and rebuilds it as a single, clean polyline — elevation intact, layer and properties preserved, and with redundant vertices weeded out.
What the tool does
Once loaded, DeAEC adds a small set of commands:
- DEAEC — converts AEC contour objects into clean polylines. Each contour becomes one tidy polyline, the elevation is kept, and vertices are simplified using the Douglas–Peucker algorithm (no destructive explode).
- DEAECSURFACE — optionally builds a TIN surface from selected contour polylines.
- DEAECABOUT — a short about screen (with a little surprise for the curious).
The conversion is not an explode. Layer, color, linetype, lineweight and elevation are carried over to the new polyline, the whole operation is a single undo step, and a short report shows how many contours were converted and how many vertices were removed.
How to use it
- Load the DLL with the NETLOAD command and select DeAEC.dll.
- Run DEAEC.
- Choose whether to process all AEC contours in the drawing or select specific ones.
- Choose whether to replace the originals or keep them.
That's it — clean polylines, ready to edit, label, or use as surface input.
Versions and compatibility
Civil 3D changed its .NET runtime across releases, so the correct build must be loaded for your version.
Available downloads:
A build for Civil 3D 2017–2024 is in progress and will be added here.
Why AEC contours still exist
Land Desktop was discontinued back in 2009, but drawings created with it never went away. They get reused, copied between firms, and reopened years later — and the AEC contours inside them survive as custom proxy objects that modern software can display but not natively edit. DeAEC exists to free that data and bring it back into a usable form.
Notes
DeAEC reads AEC contour objects; it does not create them (only Land Desktop itself could author that object type). The tool requires no third-party libraries and runs entirely inside Civil 3D.
Closing thoughts
This is a focused tool that solves one annoying problem cleanly. If you work with older Civil drawings, it can save you from the explode-and-rebuild headache and keep your elevation data exactly where it belongs.