Grade In/Out on Vertical Curve Do Not Match Tangent Grades

[technician.196935]

Hey guys, I'm a little confused on some vertical curve data I'm looking at in the profile grid view. (I'm running Civil3d 08 sp2) I have some vertical curves that should be tangent to the straight grades going into and coming out of the VC. However, when I look at the profile grid view, the grades in/out of my vertical curve are slightly different than the grades of the tangents (i.e. the tangent grade is -2.99% but the grade in to my VC says -3.03%) and I'm worried that this is effecting my K values and PVI's. I assumed the VC's would be tangent to the grades upon creation, but I'm not sure now. Any help would be greatly appreciated! Thanks. I've attached a screenshot of my grid view for a visual.

[gandocadguy]

How were the curves created? If they were created with the profile tools then they will be tangent. If you created the profile from a polyline or similar than they may not be.

[technician.196935]

I created the curves with the "Draw Fixed Parabola By Three Points" tool. Thanks!

[sinc]

Does that mean you have the problem fixed now?

[technician.196935]

No, just a statement as to how I created the curves. Apologies for the confusion. I created all of my profile information using the profile tools, excluding the "create from autocad line/spline" tool.

[gandocadguy]

No, just a statement as to how I created the curves. Apologies for the confusion. I created all of my profile information using the profile tools, excluding the "create from autocad line/spline" tool.

From the help menu:

1. Click Profiles menu Edit Profile Geometry.At the Command prompt, enter EditProfileLayout.
2. On the Profile Layout Tools toolbar, click Fixed Vertical Curve (Three Points).
3. Specify the start point.
4. Specify the second point.
5.Specify the end point.

No where does this say anything about tangent to the grade in or grade out.

I would try drawing another profile over it allowing it to create curves as you draw. That will give you a tangent curve. Then compare the differences.

[sinc]

I suspect you will get the results you are after if you create a Free Vertical Curve instead of a Fixed Vertical Curve.

[jpaulsen]

I agree with Sinc. I use Free Vertical Curve (Parameter) almost exculsively.

[brian.hailey933139]

What you did is equivilent to drawing an arc between two line segments using the three point method and eyeballing it. It may look right but the arc and line probably aren't tangent. Do as Sinc suggest and draw from PVI to PVI to PVI (etc.) and then place a curve at the PVI.