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

[jclong]

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

[steve216586]

You already have most of the work done with the curve and elevation lines every 100' in place.

Simply change view to the elevation view.

Copy the curve down to the lower end of the first elevation line's end point by drawing a PLINE.

PEDIT the pline curve copy and add vertices at every 100'

STRETCH the vertices to the lower end points of the elevation lines.

I couldn't view the drawing to test but unless there are any crazy deviations to the slope of the tunnel the lines should match pretty well. If not then you may need small, large radius fillets at the 100' points to smooth the profile.

[jclong]

You lost me with the line:  "Copy the curve down to the lower end of the first elevation line's end point by drawing a PLINE."

How do you "Copy" by drawing a new PLINE?

Let me clarify that the problem with every other attempt is that we need to be able to DRAW a NEW random length Elevation Line at ANY point between the known 100' points and then to have it INTERSECT a sloping line that lies directly below the flat curved one above.  So far, no lines ever intersect any point between the 100' markers after drawing a SPLINE through all of the points nor with a 3DPOLY.  They come close for sure, but ACAD requires exact precision to get an "intersection" between 2 zero thickness lines in space.

Do you mean to COPY the flat PLINE CURVE down to the end of the last elevation line and THEN stretch each vertex to the next elevation line 100' away on a curved path?   I'll try that to see if that's what you're talking about.  The radius of the FLAT PLINE CURVE is mostly 6,000 feet. The new sloped line needs to match that the entire length to be useful.

Either way, thanks for the reply.  Much better than I got from Subscription Support.

[hmsilva]

Curt,
to draw your spline the most accurate possible, you must have the profile elements (maybe in the schedule), to draw a profile, calculate the elevations from there.
I attached a dwg with a possible way to draw your spline, and some notes.

HTH

Henrique

[steve216586]

Yeeeeaaaaaah, I just tried my method and it doesn't work. Sorry for the "goose hunt". I think it is because it involves a 3D polyline which is possible but wouldn't stay exactly below the curved, flat, horizontal path.

[troma]

Sounds like you need Civil 3D.
Not a very helpful remark, I know.

[jclong]

Steve, Thanks for double checking and getting back to me.  I was busy trying the suggestion from Henrique so no time wasted here.   You can see the results from Henrique's suggestion in my answer to him.  

[jclong]

Henrique,  Thanks for taking the time.   I did what you said and it works for creating a profile on which to create a new spline, but the problem still remains.   With your suggestion, I can get an intersection at every point when I create a new Spline, but the points are at every 20 feet or in my test, every 10 feet.

The problem is that now, if I'm told that something needs to be added at Station mark 204+20.60 feet, that is not on any of the 20 foot or even my 10 foot profile lines.   It's about 7 3/16" away from one of the 20' markers, so now, at what elevation does it cross the Spline line at?   Drawing a new line down from that point (204+20.60) does not produce an intersection at the spline.

I can probably get very close by choosing a side view as close to a right angle to that spline and my new line and then using the spline to "TRIM" the new line and then "ID" the end point of that line.   And that's what I might have to do if I can't figure something else.  However, that means flipping my view around often on a complicate 3D model that is 107 miles away for ACAD 0,0,0 and that is asking for a crash. 

I'm trying to create a 3D profile that will allow me to find the elevation of the tunnel center at ANY new and random point along that Flat "Station" Polyline.    

As an example: When the Fire Protection contractor says that he has a 10 inch fire main at "Station 212+32.45 feet" which is at "elevation minus 54.7 feet", I'll be able to go to that Station point and draw a vertical line down to -54.7 feet and then be able to measure how far above or below the Tunnel centerline he is at THAT point without doing a bunch of math to determine where that is relative to one on my 100 foot or 20 foot or any other evenly spaced markers I may have generated.

As I said, I have determined that extruding that flat polyline up or down, produces a face that is perfectly in line.  The trick now is how to slice that face using maybe the spline that goes through all of the profile points to produce an edge and then how to turn that edge into a line that will produce an intersection with ANY new line drawn from ANY point on the project Station Line..

Does that make sense?   I have even presented this problem to the programmer that created my 3rd party piping program and hjave submitted it to the SpaceClaim people to see if their Program could solve it.  They too came to the conclusion that creating a face from the polyline above was on the right track but could not figure out how to create that sloped line from one.

Thanks again for helping.

OOPS NOTE:

Oh yes, I see that in my uploaded file, I have one extra elevation line that I was using for a test and a double line at the end that is messing up the Spline.  If anyone wants to try this, just draw any Spline through the ends of the lines at the 100' marks only and look for the hidden shorter line at the one end.
.

Curt

[jclong]

"Sounds like you need Civil 3D."    

And you are probably correct.  In fact, I believe this Tunnel was designed using Civil 3D and then ported to 2D plans using Microstation, and now handed to us ACAD Smucks as a series of files that we have to "IMPORT" to use.

However, if YOU have Civil 3D and can think of a way to gererate that sloped line for me, I would be happy to use it and give you credit.. 

Anyway, "Bertha", the tunnel boring machine was launched yesterday so the pressure is mounting..    ARGHHH   I have to lay out all of the roadway drains and get them to the pumping stations or it's going to become a swimming tunnel..  LOL

Curt

[hmsilva]

Curt,

I'm not a C3D guy, I dont use C3D for many years, but as I recall (troma may correct me if i'm wrong) when we export a 3d polyline to AutoCAD, becomes a 3dpolyne without arcs, only small straight sections...

As I said, it is preferable to draw a profile, and calculate the elevations from there, is more accurate and easier to work.

Henrique

[jclong]

I'll get the pipe and drains in one way or the other, but the problem / challenge / or question still stands:

How do you create a sloping but curved arc that perfectly matches a flat version of the same arc in the .xy at every point but with different z values so that a vertical line originating from one passes directly through the other so that it creates a selectable "Intersection" with an identifiable x,y,z value?

I've gotta move on but I'll come back if someone has a new idea...   And thanks to those that gave it a try !

Curt

[jclong]

"....to draw your spline the most accurate possible, you must have the profile elements (maybe in the schedule)....."

I forgot to say that the elevation lines at every 100' were indeed from the "Roadway Profile And Superelevation" Plans.  They actually call out that elevation every 50' but with no tick mark at 50 feet, there is the possibility of a very slight error in measuring the 10 linear feet on a curved line..   Extremely slight, but when it comes to creating an intersection between 2 zero thickness lines, any error at all is a bust.

Thanks again.

[3wood]

The projection of an arc on a slope is an ellipse arc. I don't think you can get EXACTLY same version of 3d lines from 2d flat polyline.

[troma]

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@hmsilva wrote:

Curt,

I'm not a C3D guy, I dont use C3D for many years, but as I recall (troma may correct me if i'm wrong) when we export a 3d polyline to AutoCAD, becomes a 3dpolyne without arcs, only small straight sections...

As I said, it is preferable to draw a profile, and calculate the elevations from there, is more accurate and easier to work.

Henrique

---

A 3D polyline never has curves in it AFAIK.  If you have Civil 3D you can work with curves in featurelines, or preferably in this situation you'd work with a horizontal alignment and a profile object, so you can have true curves both horizontally and vertically.

When you export these objects to 3D polylines they will be tesselated into small lines.  I believe there is a precision setting to determine how tesselated they become.

[jclong]

"A 3D polyline never has curves in it AFAIK...." 

That is correct.  In looking for a title of this thread, it should have been "How to Create a 3D ANYTHING under a Flat Polyline".

The direction I'm exploring now is to extrude the Flat Polyline to create a vertical surface.  So that every point on that surface lies directly below the Polyline.   Next, I'm trying to find some combination of commands to create a line, polyline, spline or anything that can define an edge on that surface that follows the endpoints of the Elevation Profile lines that are located every 100'.

In the ACAD help, I see a subject on:

"To Extract User-Defined Spline Curves from Surfaces, Solids, and Faces of Solids"

Under that subject, it explains:

"Use the Spline Points option to extract custom curves, not contstrained in the U or V direcitons, from surfaces and solids."

With the following steps:

1. Click Surface tab - Curves panel - Extract Isolines.

2. Select a surface, solid, or face.

3.  At the prompt, enter S to create a custom spline curve.

Begin specifiyng points on the selected surface, solid, or face.

As you click, a spline is created that passes through the specified points.

4.  Press Enter to end the command.

at step 3, when trying to select the endpoints or even anything, I see nothing happening.  Just more prompts as below:

Select point on surface or [Chain/Direction/Spline points]: s
Select first spline point or [Isoline]:
Select first spline point or [Isoline]:
Select first spline point or [Isoline]:
Select first spline point or [Isoline]:
Select first spline point or [Isoline]:
Select first spline point or [Isoline]:

No error message nor confirmations of a successful selection.

Extracting Isolines is no problem but they are only horizontal or vertical.  Even when successfully slicing the surface along the sloped profile, the sloped edge created was never selectable for extraction.

One of the things that haunts me is that this is possible in real life, so why are we not able to recreate this in ACAD?  I can't help but think that there is a way, but has anyone ever really tried this before?  I think yes, but finding that person in this Forum is highly unlikely..  No offense to anyone here.  As I've never tried this before nor have I ever had the need to try it.

So that's where I am now..  trying to "Define Spline Curves from Surfaces...."

[hmsilva]

---

@Anonymous wrote:

So that's where I am now..  trying to "Define Spline Curves from Surfaces...."

---

One more try...

Henrique

[samu3 · Accepted solution]

Hi All,

I thought this was an interesting topic, so I wanted to see what I could come up with. Please take a look at the attached file (Acad 2013).

There's (at least) two ways to get the intersecting geometry:

Draw a 3D polyline (polyline makes more sense than a spline, if it is assumed that the elevation change between station markers is linear. In real life, this is hardly the case) between the end points of the vertical elevation lines.

Extrude the created 3D poly as a surface.

Extrude the existing polyline for station markers as surface too, perpendicularly to the first surface extrusion.

Move the surfaces so that they intersect each other close to the middle area instead of just edges touching.

(Some of the steps require changing the UCS etc.)

Use intersect to create geometry where the 2 surfaces intersect.

3Dpoly and polyline will create elliptical segments, which can be joined to a spline (magenta in the drawing)

Spline and polyline will create a spline (red in the drawing)

The other method would have involved drawing a 3D polyline or spline between the end points of the vertical elevation lines, and then extruding horizantally and using projectgeometry to project the station marker polyline onto the extruded surface. The end result is the same as with the first method.

I checked 2 random points along the created elevation line (indicated by a vertical line and circle)

Let me know what you think,

Samu

[jclong]

Getting close !  I can see in your example file that any random line drawn down from the flat Station Line Polyline does indeed create an intersection through the new sloped spline below.   And, I am able to follow you through to the creation of the elliptical segments between the tips of the elevation lines, but then I'm lost where you say:

"3Dpoly and polyline will create elliptical segments, which can be joined to a spline (magenta in the drawing)

Spline and polyline will create a spline (red in the drawing)"

I am able to create the elliptical segments using BOTH "Intersect" and the "Projectgeometry" methods.  However, I must be missing something about how to create the spline from the elliptical segments.

It's amusing that after using Autocad for 28 years, there are so many new-to-me tricks and commands that I never knew existed.

Please explain how I finish..  This is exciting and really quite simple, please continue.

Thanks!

[samu3 · Accepted solution]

Hey Curt,

Very happy to be of help! I myself have used Acad since version 10, and yes there are so many commands that most are not even aware of. I really never would've used intersect and projectgeometry had it not been for the fact that I too, work in tunnel projects. I have also been using Inventor, where you project geometry all the time, and you can also do an intersection curve. So, I decided to look into similar features in current Acad 🙂

"3Dpoly and polyline will create elliptical segments, which can be joined to a spline (magenta in the drawing)

Spline and polyline will create a spline (red in the drawing)"

In my original drawing, the magenta elevation elliptical segments from station 280-> were created from your station marker polyline and my 3D poly between vertical elevation lines. Intersect created elliptical segments, which I turned into a spline in the new attachment dwg. I did this by simply typing join (no pedit, just join), and then selecting the segments.

For some reason, there is one elliptical piece next to station 285 that refuses to join the rest, and I am not sure why. Also, I seem to have missed the vertical elevation line of 285 anyway, so you will need to recreate it 😉

The red elevation spline between stations 274 and 280 were created from your station marker polyline and my spline between vertical elevation lines. Intersect autimatically created a new spline from surfaces created out of the polyline and spline.

It would be nice to have the original geometry from Civil 3D available and do some comparing with that and what we have created here...

Hello from Helsinki,

Samu

[jclong]

Thank you Samu,

I have left the office for the weekend but will return Monday to go through the steps you have explained. I will also look up the original "BT99" Station line that I received as a DGN (Microstation) file for you or anyone else to explore.  This poor file had been through other conversions by the time it arrived here so it's no surprize to me that there could be errors.  In addition, the file I received was scaled to be "Decimal Feet" with elevations rounded off to 2 decimal places so I'm sure there is a small error added to the elevations. I don't believe the small errors in elevation will affect the outcome of this exercise and I'm sure that the Tunnel itself will be nowhere as accurate when built.  But as a CAD exercise, there is no reason this can't be perfect.  Let the construction phase produce the errors, but there is no reason the CAD model can't be perfect.

I know what the radius should be for each arc that created the station line curve so if necessary, I might recreate it to see if I can get past any errors.

Up until now, almost all of my 3D modeling has been with Solids and I have only recently been seeing that Surfaces can be just as important.  I also own Solidworks, SpaceClaim Engineer and Rhinoceros 3D 5.0 but have had very litle time to sit down and really use them for surfaces until this problem came along. I have seen similar operations in SpaceClaim Engineer where curved lines were "pulled" into surfaces to intersect other faces or surfaces to produce an intersecting line.  That is where I got the idea that this must be possible.

Sadly, many of the Contractors that I work with in the construction industry are still using only 2D CAD and consider even regular AutoCAD as high technology beyond what they need.  Also sadly, this tunnel project is one that has a true 3D model origin that was later used to produce the 2D paper plans. And unfortunately all of the MEP team other than myself and the HVAC contractor have chosen to use and work in 2D for the MEP coordination.  I have already been pointing out many of the errors that have come from using a 2D section and plan to work out 3D designs.  I am horrified when I attend a meeting and people lay down a 2D paper plan of their work with no other trades included in their plot and then think that they can discover and prevent conflicts by working the way we used to work way back in 1993.

I will welcome any other attempts to work out this same challenge from you or other people in this Discussion Group. As far as I'm concerned, this is not a "closed" exercise though I WILL consider this AND mark this as an "Accepted Solution".  But as I said, I'll share the Microstation file that I received at the beginning of this project along with some of the PDF files that define the Tunnel Centerline elevations when I return to work Monday so that others can have the opportunity to work with a real world construction issue if they have the time and desire to learn from this.

Thanks to all that have helped, and Cheers,

Curt Long

Seattle Area, USA