Create Feature Lines from Objects - Problems assigning elevations from a surface

[kcad1]

Hi,

I'm trying to create a feature line from a polyline. I'd like it to assign elevations from the existing surface. I'm selecting From surface and am checking Insert intermediate grade break points. However, it seems to ignore most all of the existing surface's TIN lines. It just adds a couple of elevation points from where it crosses the existing TIN, but ignores the majority of them. (So it does, at least to a small degree, recognize the existing surface)

I don't have the Weed Points check box checked.

I'm using Civil 3D 2012.

I've had sucess plenty of times in the past doing this, and am not sure why this project seems to be causing problems. If anyone has any suggestions, I would definitely appreciate it. Thanks!

[Pointdump]

K,

Post your drawing. Does it do that with just that one drawing, or all?

Dave

[kcad1]

The file I was trying to post was too big, even a clipped version I made. So I basically created a simple test version and have attempted to post it. I am still having the same problem on this simple test version.

In the file, I have a couple of polylines (on a while-colored layer), which I have attempted to create feature lines from (on a blue colored style). If you look at the file, the white polylines will probably be hidden under the blue feature lines. Only a few elevation points were added by Civil 3D (and only on the longer polyline). Elevations were not added to every point that the polylines crossed a TIN line.

(A side note is that this file is in meters. And it appears, from the survey and proposed grading files we received from the Architect, that linework has been scaled up x1000 to put it in millimeters. I'm used to working in feet, so this has been a bit confusing in itself....)

To answer your question, Dave, I haven't been having this problem with other projects in the recent past. I suppose I should try to do some more tests to see to what extent I might currently be having this issue. I do seem to recall a long time ago having a similar issue, which confused me at that time.

Thanks for your reply Dave.

Kyle

[Pointdump]

Kyle,

I can't figure it out. I opened your drawing in C3D 2014 and found the same thing you did. I checked a drawing of my own and had no problem draping a feature line across the surface.

Try a couple of your older drawings, and see if things work. How was that surface built, from contours?

This is baffling.

Dave

[Jeff_M · Accepted solution]

The problem is in the coordinates. AutoCAD, and hence C3D, can only use 15 significant digits so it gets bamboozled in large coordinate systems. If you move your defining contours and polylines closer to 0,0 the draping works fine. Here is a random point located inside the surface boundary: X = 272387399.748     Y = 8663395192.045

8 billion units north of 0 is a wee bit far...

[kcad1]

Great information Jeff! Thanks.

The backstory is that when I first looked at the survey, I checked for what Civil 3D stuff was in it. Long story short, it appeared that there were points (set to not display) much closer to 0,0 and set up for meters. Someone (the surveyor or architect?) apparently must have scaled the linework up by 1000 to get the drawing to millimeters (but left the points behind, which was a nice clue as to the origin of the file).

I'm new to using metric units (or SI units?). Kind of get the feeling that the files should not be scaled up by 1000 to millimeters, but that's not relevant to this thread...

Jeff, I'll check out what you're saying when I'm in the office tomorrow. But it does make sense to me. I'll check off that the problem's solved after I test this out.

Dave, thanks for taking a look at the file (and getting me to post it in the first place). I appreciate both of your help!

[kcad1]

Just to follow up, I recreated the existing surface at coordinates much closer to 0,0. Assigning elevations to a feature line created from a polyline worked perfectly. It picked up every elevation where the polyline/feature line crossed a TIN line.

Problem solved. Thanks again for the help!

[jmayo-EE]

Jeff hit the issue on the head but I think you can avoid moving the FLines if you use the Assign Elevations From Surface after you create the Fline. This has worked for me. I have seen issue with surface elv's when they are assigned during creation and the fix up fine by rerunning the command after.

[Jeff_M]

John, I tried that and still no go with this drawing.

[jmayo-EE]

Wow Jeff I did not test & I do believe the facts presented here but I will tell you this is the first case I have seen that that did not work and I regularly have  coords of approx. 500000,600000. Im probably just under the limit. 😉

[Jeff_M]

Heh, not sure where that limit lies, John, but it's likely to be long before it gets another 8 billion units further away from 0,0 than you. 

[Pointdump]

Jeff,

Kudo to you! Like John, I tried to Assign Elevations From Surface after I created another FLine, and no go. Only when I moved the surface closer to 0,0 was I able to Drape the FLine.

Thanks for solving yet another one!

Dave

[jmayo-EE]

"Thanks for solving yet another one!"

Jeff has a habit of doing that. 🙂

[kbarnettza]

I just stumbled across the same problem, and, as with the OP - my coordinate values are large (in metres, the coordinate system uses the Earth's equator as 0 for X - we are over 2 million away) . Jeff's method matches the solution we use for hatch patterns - except - in the case of hatch, a temporary custom UCS works. I found another way ... keeping the model at huge coordinates ... Extract the tin surface to a solid then use AutoCAD's PROJECTGEOMETRY command to drape the acad lines or poly-lines on the solid. This method finds the triangle intersections even with huge coordinates.