How to create a 3D Polyline or Spline directly under a Flat Polyline

[Anonymous]

I've also sent this to support but will post here too:

I'm working on a Tunnel Project where they reference everything with a flat but curved Polyline that has what are known as Station Points.  Every 100 feet along this line is a number.  Between each 100' mark are tick marks that intersect this Polyline every 20 feet.  There is a schedule for the depth of the center of this tunnel at every 100' mark, so it's easy to draw a vertical line down from each 100' mark to the depth or hight of the center of the tunnel.

The challenge is to be able to discern the elevation of anything that lies between those 100' points by drawing a line down until it intersects a 3D version or Spline drawn through the tips of those vertical depth marker lines.  This new line MUST lie exactly under the Flat Station Line (polyline) above so that any line pulled vertical through it produces an intersection that can be listed to find the missing 'Z' value.

I've tried many different techniques and passed this on to other experts but no one so far has been able to create a matching but sloped line directly below the flat polyline master that creates intersections other than the ones at the tips of the vertical lines drawn at every 100' mark.

See the attached ACAD 2013 file. The vertical lines are drawn in already at each 100' marker.   Sorry about the origin being so far away, but this is how the files are coming in from the Engineering firm using Microstation DGN files.  Feel free to move the model closer to ACAD 0,0,0.  I'm only looking for a way to create the matching line that follows the slope of the tunnel..  One trick I've been exploring is to EXTRUDE the 2D polyline to create a face and then try to slice that face with a spline drawn through the points as the cuttin edge to create an edge that could then be turned into a line of some sort.

Thanks from Seattle

Curt

[SEANT61 · Accepted solution]

A possible variation - eliminate the need for the 3d Curve.

From the Right view and with OSNAPZ = 1, create a spline by snapping to the 100’ increment drop lines.   Extrude that into a surface.  Place a Point entity at the desired Station Offset.  With WCS active use the _PROJECTGEOMETRY command with the UCS option.  ID the new, projected point to find respective Z value.

[samu3]

Curt,

I know what you are saying about the 2D drawings. It seems that there is still a lot of the "2D is just fine" approach out there, probably even more so when it comes to tunnels, because tolerances are not as high compared to many other fileds. However, I think you hit the nail on the head by saying that there is no reason this could not be executed correctly as an exercise in Acad, regardless of errors that may be produced elsewhere in the process.

Luckily, lately I've been introduced to Building Information Modelin based projects, and I do hope that the rapidly growing interest in and (almost near necessity) of using BIM will bring standards and requirements to a more unified and well-refined level!

Sean, I really like your method - very clean and straight forward! 🙂

Samu

[Anonymous]

Sean,    Very nice !!    Another good solution and adding to my learning curve.  Thanks.  I'm finding more and more reasons to use surfaces.

[Anonymous]

As I said earlier, for anyone that wants to continue this exercise for whatever reason, I'll upload the Station Line drawing as it was imported and include some JPG views of the Super Elevation PDF plans that spell out the elevations at every 50 feet.  The JPG files turned out really large so I'll have to add at least one of them in the next post.

I have left the Station Line file where it was.  It was created to represent decimal feet as the base unit so you can leave it as is for easy entry of the elevations or scale it up by a factor of 12.

I included a few green elevation lines at the start that have the correct value per the PDF plans and I have drawn in layer "temp" some straight lines from point to point at every 100 foot marker to help identify the middle of each arc segment or the 50 foot point along the Station Line.

I don't expect anyone to use these, I just make them available in case you want to explore deeper using some real world tunnel plans.

Cheers,

Curt

[Anonymous]

And here it the remainder of the Super Elevation plans.

Curt