rustysilo Posted February 19, 2009 Share Posted February 19, 2009 I'm trying to model a roadway in 3d with regular AutoCAD as opposed to Civil 3d (just for fun mostly). My idea was to draw a cross section of the roadway and then sweep it along the centerline which is a 3d polyline, but the section is twisting as it sweeps down the 3d poly. Is there any way to keep it from twisting or is that just the natural behavior? Maybe a better option might be to copy this cross section at intervals along the 3d poly and then loft them together using the centerline as a path? Quote Link to comment Share on other sites More sharing options...
MaxwellEdison Posted February 19, 2009 Share Posted February 19, 2009 I'd loft a cross-section using a spline for a path. You might need to adjust the sections to be perpendicular, but you can easily change the elevation at each node for a very realistic path. Quote Link to comment Share on other sites More sharing options...
rustysilo Posted February 19, 2009 Author Share Posted February 19, 2009 I tried loft and it gave me this message when I went to select the path: "The selected entities are not valid." I noted that I cannot loft a 3d poly (according to HELP) so I converted to regions and tried again. Got the same message. Quote Link to comment Share on other sites More sharing options...
MaxwellEdison Posted February 19, 2009 Share Posted February 19, 2009 I tried it with a 2d cross section lofted using a spline as a path and it worked fine. Are you using a spline or a 3d poly for your path? Quote Link to comment Share on other sites More sharing options...
rustysilo Posted February 19, 2009 Author Share Posted February 19, 2009 3d poly. I don't know if a spline would be accurate enough should a user do this for something more than just a presentation. Quote Link to comment Share on other sites More sharing options...
rustysilo Posted February 19, 2009 Author Share Posted February 19, 2009 I tried it with a 2d cross section lofted using a spline as a path and it worked fine. Are you using a spline or a 3d poly for your path? What shape is the path? I'm trying using sort of an S curve that dips down and back up. Quote Link to comment Share on other sites More sharing options...
Secretagdan Posted February 19, 2009 Share Posted February 19, 2009 Have you tried the 'SWEEP' command? Quote Link to comment Share on other sites More sharing options...
MaxwellEdison Posted February 19, 2009 Share Posted February 19, 2009 Here's my loft before and after. 3D ROAD - BEFORE AND AFTER.dwg Quote Link to comment Share on other sites More sharing options...
shift1313 Posted February 19, 2009 Share Posted February 19, 2009 there was a user that came on here awhle back trying to draw a race track. When you are setting up the sweep there is a Twist option. Have you played with this at all? Quote Link to comment Share on other sites More sharing options...
rustysilo Posted February 19, 2009 Author Share Posted February 19, 2009 No because I don't want it to twist, but it twists slightly anyway even when twist is not used. I guess due to the way the 3d poly is. Quote Link to comment Share on other sites More sharing options...
rustysilo Posted February 19, 2009 Author Share Posted February 19, 2009 Here's a grab of the one I did using sweep. Notice how the first one is horizontal, but the last one is tilted. I'm doing one that has a crown (3% slopes) with curb & gutter in this case. Quote Link to comment Share on other sites More sharing options...
MaxwellEdison Posted February 19, 2009 Share Posted February 19, 2009 Loft does not twist the road surface. The image I attached below took longer to add height to the vertices of the spline than anything else, Quote Link to comment Share on other sites More sharing options...
rustysilo Posted February 19, 2009 Author Share Posted February 19, 2009 But do a front or side view of it, then use 3dorbit to rotate about that axis. Look closely at the road and you will notice it tilts ever so slightly around the curves, or at least it sure looks like it to me. Create some sections with sectionplane at various points perpendicular to the roadway and when you generate the 2d sections you will see. It looks to me like when the 3dpoly has vertical changes around the curves it twists slightly. Look at my screen grab. I'm tellin you man IT'S TWISTED!!! Please tell me I'm not going crazy. Quote Link to comment Share on other sites More sharing options...
shift1313 Posted February 19, 2009 Share Posted February 19, 2009 can you do a loft, take your 3d poly and offset it and use both of those as guides? that way you ensure it doesnt twist. Quote Link to comment Share on other sites More sharing options...
rustysilo Posted February 19, 2009 Author Share Posted February 19, 2009 I tried copying the 3d poly to the edges (can't seem to offset it) and do that earlier, but it didn't work either. Quote Link to comment Share on other sites More sharing options...
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