Last updated July 28, 2026
ATC converts arcs into circles. Select any number of arcs, and each one is replaced by a full circle sharing its centre and radius — and, importantly, all of its other properties. Layer, colour, linetype, lineweight and thickness all carry across, so the new circles sit in your drawing exactly as the arcs did.
Anything in your selection that is not an arc is ignored, so you can window a busy area without being careful about it.
It is by Zoltan Toth of ZOTO Technologies in Melton, Victoria — which makes it one of the few routines in this library written locally.
Why you would want this
Trimmed geometry. You draw a bolt circle or a set of holes, trim the circles back while working on something else, and later need them whole again. AutoCAD has no command that closes an arc back into a circle, so the alternatives are drawing new circles and matching their properties by hand, or snapping a fresh circle to the arc’s centre and endpoint.
Imported data is the other common case. Files that have come through a translator often arrive with circles broken into two or four arcs. Selecting the lot and running one command is considerably faster than repairing them individually.
How the property carry-over works
Worth explaining, because it is the part that makes the routine worth having rather than a novelty.
Rather than reading the arc’s centre and radius and drawing a new circle, the routine takes the arc’s complete entity definition, swaps the entity type from arc to circle, and drops the two values that only an arc has — its start and end angles. Everything else in the definition is left untouched and comes across automatically.
That is why the description can promise “all the properties of the arc it replaces” rather than a specific list: the routine never enumerates them, so it cannot miss one. A property added to AutoCAD ten years after this was written would still carry across.
The circles are new objects, not modified arcs, so the original arcs are gone when it finishes.
Command reference
The file defines a single command, ATC — arcs to circles.
How to load it
Unzip Atc.zip and load ATC.LSP with APPLOAD, or add it to the Startup Suite. No support files. Our AutoLISP guide covers loading.
Step-by-step usage
- Type ATC. It prompts “Select arcs to convert to circles:”.
- Select. A window over the whole area is fine — the selection filter accepts arcs only, so nothing else is touched.
- Press Enter. Each arc becomes a circle with the same centre, radius and properties.
Worth checking one result against the original layer and linetype the first time, just to satisfy yourself the carry-over is doing what it says.
Compatibility notes
Version 1.0, no date in the file. It works purely by manipulating entity definitions, which is the most stable thing you can do in AutoLISP — the arc and circle definitions have not changed in decades. Written-for rather than tested-on, but this is the kind of code that ages well.
Plain AutoLISP with no dialog boxes and no Express Tools calls, so nothing requires the full product; LT users on LT 2024 or later, the release that brought AutoLISP to LT, should be able to run it. See what runs on AutoCAD LT. It replaces geometry, so run it on a copy the first time.
Download
| Name: | ATC |
| Description: | This program takes any number of arcs and converts them into circles. Each circle is a new object with all the properties of the arc it replaces. Non-arc objects are ignored. |
| Type: | AutoCAD AutoLISP Routine |
| Author: | Zoltan Toth |
| File Size: | 1 Kb |
| Cost: | Free |
| Worked on: | AutoCAD |
| Download File: | Atc.zip |
Related routines
- C2P — the other common conversion, line or arc to polyline.
- Trim to Point — the operation that created your arcs in the first place.
- Best of LISP collection — more drawing repair utilities.