An InRoads user asked for Mark's help with a seemingly simple question that turned into quite an in depth answer.  

Here is Part 1 (out of 2):  

Hello Mark! 

I hope you are well and involved in awesome projects as per usual! I have a question regarding alignments. Attached is a sketch of what I am trying to achieve and I would like to know how the expert would approach this.

I figure I can draw the alignment at one elevation in order to get the curve and then import and apply flow by editing the vertical in a profile... right? But what if I already have the alignment except for the curve, how could I most efficiently approach inserting a curve? Which method would be most mathematically accurate?

I really appreciate your help and if there is anything more that you need please let me know!

Sincerely,

Alejandra

Here is the Zen Dude's response:

Hi Alejandra!

First, just to make sure I understand what's going on - You first laid out your horizontal alignment with only PIs (no curves) and then you created a Profile and laid out your vertical. And now you want to add a curve (or two) into the Horizontal, right? And further, are you planning to redesign the vertical after you add the curve(s) or are you going to attempt to salvage the vertical that is already done?

Civilly yours,

- mark

Mark,

Thank you for your quick response.  :-)

Yes, the vertical was laid out using the invert and slope elevation on the sketch, without the curve. It was actually drawn in MicroStation and imported as a horizontal and vertical alignment. And no, we do not plan to redesign the vertical after we create it. Does it make a difference for which method to choose if we plan to redesign?

-Alejandra

Okay Alejandra! This is a really good question that touches on something that many people are unaware of, but it's really important. And because you already have your vertical done the answer isn't so straight forward.

The quick answer that I would have given you a couple years ago is (and just to get you pointed in some direction . . . then I'll follow with another twist on this problem):

1)  Go to Check Integrity and delete that curve you placed because I noticed that it has some issues with it. Namely it's non-tangent (the real problem) and it's also out of order, element-wise as shown by the 'non-coincident' messages in the Check Integrity tool.

2)  Then go to Geometry > Horizontal Curve Set > Define Curve and place your curve or curves (I placed two, but I see from your sketch that you might really only need one). I'm assuming that you have some familiarity with the Define Curve command.

3)  Then create your Profile and view the currently laid out Vertical alignment (this is where some extra work will have to be done). I also annotated it so I could see exactly how it was constructed.

4)  Now this is minor in your case, but we're engineers ; ) . . . after adding the curves you'll see that the horizontal alignment is now shorter because it's more "direct" from the beginning to the end. The problem is that the Vertical alignment is stored based on the stationing of the 'original' alignment layout without the curves. The last point on the current Vertical alignment is stored station-wise relative to the last point on the originally constructed horizontal, and is no longer in the same position vertically as it was before adding the curves. Are you following this? This topic is best covered in person, and I can't quite type as fast as I can think so I'm losing some of my thoughts.  : P

Notice on the profile above that it doesn't vertically annotate the last point because the stationing is 14+ , and the new horizontal actually ends now at 13+ , and isn't long enough anymore to be able to view the entire 'originally' laid out vertical alignment.

Look at these reports (specifically noting the POE) of the before and after Horizontal alignment geometry and the currently unchanged vertical alignment report that still shows the vertical based on the original horizontal without the curve. 

5)  So, what you have to do is edit the Vertical to re-establish your key vertical layout construction locations, based on whatever original criteria you used. You can do this with the Vertical Table Editor or just empty your Vertical alignment placeholder and rebuild it. Your alignment is pretty simple so you could probably just lay it out again pretty fast. But on a long alignment with a lot of vertical control points, this could get a little tricky and involve more work that you might want to do.

This answer is getting quite lengthy and I wanted to get this off to you so you could start working on it rather than waiting.  I'll send along Part 2 shortly.  

Civilly yours,  

-zen