https://forums.autodesk.com/t5/autocad-forum/unable-to-offset-polylines/m-p/13671206#M350302 <P>As others have said there are way to many vertices but if you want to use the 3dpoly then either use&nbsp;<a href="https://forums.autodesk.com/t5/user/viewprofilepage/user-id/69526">@Kent1Cooper</a>&nbsp; program or you can use the Boundary command to create a 2dpolyine.</P><P>For example, create a polyline (red) as shown below.</P><P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="leeminardi_0-1749346229827.png" style="width: 400px;"><img src="https://forums.autodesk.com/t5/image/serverpage/image-id/1541413iEF186F8520642896/image-size/medium?v=v2&amp;px=400" role="button" title="leeminardi_0-1749346229827.png" alt="leeminardi_0-1749346229827.png" /></span></P><P>Using the boundar command pick a point inside the closed area.&nbsp; This will yield a 2d polyline.</P><P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="leeminardi_1-1749346328519.png" style="width: 400px;"><img src="https://forums.autodesk.com/t5/image/serverpage/image-id/1541414i23697A181FC046B3/image-size/medium?v=v2&amp;px=400" role="button" title="leeminardi_1-1749346328519.png" alt="leeminardi_1-1749346328519.png" /></span></P><P>&nbsp;</P><P>Trim off the extraneous geometry and then use offset as needed.</P><P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="leeminardi_2-1749346487959.png" style="width: 400px;"><img src="https://forums.autodesk.com/t5/image/serverpage/image-id/1541415iCCA666ECEB9DA969/image-size/medium?v=v2&amp;px=400" role="button" title="leeminardi_2-1749346487959.png" alt="leeminardi_2-1749346487959.png" /></span></P><P>&nbsp;</P><P>&nbsp;</P> Sun, 08 Jun 2025 01:34:54 GMT leeminardi 2025-06-08T01:34:54Z https://forums.autodesk.com/t5/autocad-forum/unable-to-offset-polylines/m-p/13669391#M350243 <P>These road outlines were converted from splines into 3D polylines. FLATTEN command is not converting them the 2D polylines and I think for this reason I am unable to offset each of them 906 mm outwards. Can anyone advise on why these objects cannot be offset? see attached file...</P> Fri, 06 Jun 2025 10:58:17 GMT https://forums.autodesk.com/t5/autocad-forum/unable-to-offset-polylines/m-p/13669391#M350243 Luke_Daniels 2025-06-06T10:58:17Z https://forums.autodesk.com/t5/autocad-forum/unable-to-offset-polylines/m-p/13669422#M350245 <P>it appears as there a far to many vertices in the lines</P><P>On&nbsp; new layer, draw splines with about ten equally spaces vertices along your lines.&nbsp; the splines will offset with no problem.</P><P>Can you simplify your lines?</P> Fri, 06 Jun 2025 11:19:57 GMT https://forums.autodesk.com/t5/autocad-forum/unable-to-offset-polylines/m-p/13669422#M350245 parkr4st 2025-06-06T11:19:57Z https://forums.autodesk.com/t5/autocad-forum/unable-to-offset-polylines/m-p/13669443#M350246 <P>You can't offset because there are some near zero z value vertices and it won't offset a 3d poly (even though it shows a preview!).</P><P>I never have much success with FLATTEN, I usually explode and then set the elevations to zero before joining to create the 2d polyline as per the video.</P><P>Also you could OVERKILL as there were a lot of overlapping segments.</P><P>&nbsp;</P><P><div class="lia-vid-container video-embed-center"><div id="lia-vid-6373941396112w517h517r291" class="lia-video-brightcove-player-container"><video-js data-video-id="6373941396112" data-account="6057940548001" data-player="default" data-embed="default" class="vjs-fluid" controls="" data-application-id="" style="width: 100%; height: 100%;"></video-js></div><script src="https://players.brightcove.net/6057940548001/default_default/index.min.js"></script><script>(function() { var wrapper = document.getElementById('lia-vid-6373941396112w517h517r291'); var videoEl = wrapper ? wrapper.querySelector('video-js') : null; if (videoEl) { if (window.videojs) { window.videojs(videoEl).ready(function() { this.on('loadedmetadata', function() { this.el().querySelectorAll('.vjs-load-progress div[data-start]').forEach(function(bar) { bar.setAttribute('role', 'presentation'); bar.setAttribute('aria-hidden', 'true'); }); }); }); } }})();</script><a class="video-embed-link" href="https://forums.autodesk.com/t5/video/gallerypage/video-id/6373941396112">(view in My Videos)</a></div></P><P>&nbsp;</P> Thu, 12 Jun 2025 07:44:39 GMT https://forums.autodesk.com/t5/autocad-forum/unable-to-offset-polylines/m-p/13669443#M350246 will_young 2025-06-12T07:44:39Z https://forums.autodesk.com/t5/autocad-forum/unable-to-offset-polylines/m-p/13670039#M350266 <P>As mentioned, even a geometrically planar 3D Polyline cannot be Offset.&nbsp; That's one reason I made <STRONG>Pline3Dto2D.lsp</STRONG>, <A href="https://forums.autodesk.com/t5/visual-lisp-autolisp-and-general/trouble-converting-3d-to-2d-polyline/m-p/8273224/highlight/true#M99475" target="_blank" rel="noopener">&gt;here&lt;</A>.&nbsp; See the comments at the top of the file.&nbsp; I tried it in your drawing, and the results were Offsettable [without reducing the number of vertices].</P> Fri, 06 Jun 2025 17:14:53 GMT https://forums.autodesk.com/t5/autocad-forum/unable-to-offset-polylines/m-p/13670039#M350266 Kent1Cooper 2025-06-06T17:14:53Z https://forums.autodesk.com/t5/autocad-forum/unable-to-offset-polylines/m-p/13671206#M350302 <P>As others have said there are way to many vertices but if you want to use the 3dpoly then either use&nbsp;<a href="https://forums.autodesk.com/t5/user/viewprofilepage/user-id/69526">@Kent1Cooper</a>&nbsp; program or you can use the Boundary command to create a 2dpolyine.</P><P>For example, create a polyline (red) as shown below.</P><P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="leeminardi_0-1749346229827.png" style="width: 400px;"><img src="https://forums.autodesk.com/t5/image/serverpage/image-id/1541413iEF186F8520642896/image-size/medium?v=v2&amp;px=400" role="button" title="leeminardi_0-1749346229827.png" alt="leeminardi_0-1749346229827.png" /></span></P><P>Using the boundar command pick a point inside the closed area.&nbsp; This will yield a 2d polyline.</P><P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="leeminardi_1-1749346328519.png" style="width: 400px;"><img src="https://forums.autodesk.com/t5/image/serverpage/image-id/1541414i23697A181FC046B3/image-size/medium?v=v2&amp;px=400" role="button" title="leeminardi_1-1749346328519.png" alt="leeminardi_1-1749346328519.png" /></span></P><P>&nbsp;</P><P>Trim off the extraneous geometry and then use offset as needed.</P><P><span class="lia-inline-image-display-wrapper lia-image-align-inline" image-alt="leeminardi_2-1749346487959.png" style="width: 400px;"><img src="https://forums.autodesk.com/t5/image/serverpage/image-id/1541415iCCA666ECEB9DA969/image-size/medium?v=v2&amp;px=400" role="button" title="leeminardi_2-1749346487959.png" alt="leeminardi_2-1749346487959.png" /></span></P><P>&nbsp;</P><P>&nbsp;</P> Sun, 08 Jun 2025 01:34:54 GMT https://forums.autodesk.com/t5/autocad-forum/unable-to-offset-polylines/m-p/13671206#M350302 leeminardi 2025-06-08T01:34:54Z https://forums.autodesk.com/t5/autocad-forum/unable-to-offset-polylines/m-p/13678156#M350496 <P>Thanks Lee, much appreciated.</P> Thu, 12 Jun 2025 07:25:47 GMT https://forums.autodesk.com/t5/autocad-forum/unable-to-offset-polylines/m-p/13678156#M350496 Luke_Daniels 2025-06-12T07:25:47Z