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Issues with sweep / extrude (inexperienced user)

michaelv976
Contributor

Issues with sweep / extrude (inexperienced user)

michaelv976
Contributor
Contributor

Hi,

 

I'm trying to create some 'basic' 3d solids to assist with explaining some concepts for a report relating to a road drainage project. The section will have identical concrete barrier each side of a consistent width roadway. The cross section should be a perfect mirror. It follows a 3d alignment that has both vertical and horizontal curvature in places, created by others.

 

Though I am sure there are better packages / ways to do this, it's something I am somewhat familiar with. I intend to increase the transparency of the road aspects to see the drainage underneath. So I wanted to have the concrete barriers as solids and create a thin crust (perhaps 0.05m thick) for the road surface.

 

My problem is I cannot get solids to extrude / sweep. I figured I needed the extruded shapes to be perpendicular to the path at the start. So I took the 7 points of interest then created offsets to a common Z lower than all 7 points (say RL 13.0). I then drew 3d poly's from each of those 7, RL 13.0 points and made them perpendicular to the actual 7 lines, so that I thought I would end up with the shape (crudely) sketches in green, rotated backwards to be perpendicular to the start of the section. I attempted to extrude and sweep this along several of those actual 7 (3d) polylines. It would not work and I get error code 40021.

 

I then broke it down and just kept the rotated shape for the concrete barrier on the left. That extruded along line 1. So I tried the exact same thing in reverse on the right hand side, same shape in reverse, extruded along Line 7. Error code 40021. From what I have read this can imply an overlap, yet there are no real tight curve along the road alignment?

 

I cannot understand how it's (in my mind) the exact same procedure yet it doesn't work. Are there fundamental things I am not understanding when it comes to using extrude and sweep?

 

michaelv976_2-1689482137076.png

 

Thank you in advance

 

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leeminardi
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Mentor

"My problem is I cannot get solids to extrude / sweep. I figured I needed the extruded shapes to be perpendicular to the path at the start."

 

As I understand your goal you would like to create a swept solid from a given section.  The section to be swept  should be a 2D closed polyline (not an "extruded shape").  The section does not need to be perpendicular to the path start.  The normal vector to the 2D shape is used to align the cross section perpendicular to the segments of the 3dpolyine. What can be challenging is to control the twist of the section relative to the path.  The sweep twist angle can affect whether or not AutoCAD will generate a swept shape. 

 

You mention that the "3d alignment that has both vertical and horizontal curvature in places".  A 3dpolyline can only have straight segments.  Is it possible to use a spline instead of a 3dpoly?  If so you could position sections along the spline which you can individually rotate to control twist and then use loft to create the solid.  I created a VLISP program to help me position sections along a spline in 3D.  If you can use splines I can post the code an how to use it.

 

Can you post a sample file of the path and the section with an explanation of how they should be used to create the desired sold?

lee.minardi
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michaelv976
Contributor
Contributor

Hi Lee,

 

I've cut and paste the 7 x 3d strings in the attached.

 

Also included is the rough section, or what I was trying to do, at the very end of the blue lines as shown - though I probably would split it up into the two side barriers plus a section in the middle representing pavement.

michaelv976_0-1689533430525.png

There's also the section that worked for me in the centre of the drawing.

michaelv976_1-1689533617658.png

3am here now, so I'm going to try and get some shut eye. Thanks for looking into it...

 

Mike

 

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leeminardi
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Accepted solution

My first goal was to create a polyline (2d) on the XY plane such that its first vertex was at the section's midpoint.  I also wanted to make sure that the section's line of symmetry was parallel to the Y axis.  To help me I created a line  (cyan) between the two outer corners then moved it up (red line)to the apex of the section.

 

 

leeminardi_1-1689534975413.png

After creating a reference rectangle on the XY plane (red) align was used to position the 3dpoly parallel to the XY plane (magenta).  A polyline was created by snapping to the vertices of the 3dpoly making sure to start at the midpoint.  The result is the 2d polyline (green).

 

leeminardi_0-1689534680772.png

 

Your 3dpoly has too many vertices too close together so I created a new 3dpoly and then used sweep with the closed polyline (green) and the simplified 3dpoly . 

leeminardi_2-1689535370286.png

 

leeminardi_3-1689535414329.png

 

 

 

lee.minardi
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michaelv976
Contributor
Contributor

Thank you Lee,

 

Is the issue the total number of vertices (long 3d line) or actual proximity? In other words if I only asked it to run that section over 50m would it have had any more chance of working compared to the (from memory) 1.5km length? In general vertices are created every 5m along the alignment, but of course there are 7 points (min) in any one cross section.

 

I've had issues in the past but sort of found some sort of workaround whereby perhaps the polygon shape isn't exactly perpendicular and gets extruded/swept on a skew.

 

For what I am trying to achieve (a rough visual to explain design concepts) your approach seems fit for purpose.

 

Thanks again.

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