CROSS SECTION PROBLEM

[rmk]

I'm creating an as built for a roundabout and need to calculate volumes of several different materials.
I have a final grade surface and a final roadway surface. I've created feature lines for the gutter lines, back of curbs and center line of the drive lanes.
I've dropped the back of curb line to the bottom elev. of the conc on both sides-then offset them 1 ft. outward to represent the extents of the base material.
I then used those 3d plines and created a sloped surface representing the top surface of base course, then copied and lowered that surface 1ft to define the
bottom of the base course.

my cross section for the final grade and final surface looks correct.

here's the problem. when I sample these two surfaces to display in the cross section, the alignment of the surfaces is shifted horizontally by about a foot.
if you measure the width of the surface both in plan view and section, they measure the same.

note: my 3d polylines were created by drawing a series of arcs around the roundabout, not a true geometric circle.

Any ideas as to what is causing this issue and any solution or work around would be very much appreciated. Another guy in the
office who is our resident civil 3d expert (over 12 years of experience in nothing but LD and C3D can't figure out why).

[BlackBox]

Why not just extract the respective surfaces you need from your Roundabout's Corridor?

Not that I use it for my own work, but even QTO can do this, as I understand it.

[rmk]

It's an as built situation, so we can't really use an assembly to create the shapes for a corridor.

[BlackBox]

It's an as built situation, so we can't really use an assembly to create the shapes for a corridor.

Pretty sure that you can simply modify your targets, but that's for you to decide - you've already created the surfaces at this point.

If you post a sample drawing, perhaps someone can help to identify the problem more easily than having to attempt to break their own setup to reproduce the behavior?

Cheers