Fixing a Alignment by Object

One of the "complaints" about using the "Create Alignment by Object" to convert a polyline object into an alignment is that the tangents and PI are missing.  This makes an edit of the converted alignment a little difficult in some instances.   Well, they aren’t missing – just hidden. To find out how – join me after the jump.

So – Here is our polyline – there nothing special about it. 


Most of us either have alignments that have started this way. I hate the workaround needed to adjust this alignment because of the lack of the PI.  

Please note, I stumbled upon this last week and I have not fully tested the ramifications of this edit.  Your mileage may vary.  I haven’t really nailed this procedure down and I hope this isn’t a bug that those QA folks will write-up as a defect.  Maybe the can expose a way to create those tangents automatically?!

alignment grips 

Okay – here is our alignment from the ByObject Creation (please ignore the fact this looks different – it is because of timing of my Snagit Captures)

We need to enable the grips as shown above.  You should notice that the PI is missing.

step 1 - grap the round grip and drag

Well, find one of those circle grips at the PC and PT, grip it, and rip it out as shown.

enabling the grips

Take a look at the resulting alignment grips.  (You may need to grab and attempt to grab the PC)   Those two square grips become visible.  Grab the one closest (in this case) to Station 2+60.  Drag that grip out to connect it with the Tangent that you created earlier.

alignment edit complete 



  1. Steve Boon says:

    I’d like to offer a refinement to your method.

    Make a copy of the polyline with no displacement, then fillet the copy with zero radius. Use the Create Alignment from Polyline tool, but make sure that the Erase existing entities checkbox is turned off. Now when you grip edit the alignment you can use snaps to quickly set the tangent endpoints to the correct location, and you can reset the curve to its original radius afterward.

  2. You make this look so easy, but …
    Tell me how . . . when someone (a designer) must export his alignments in simple autocad (even 2007). Then the alignments transform into LWPOLYLINE dividing the whole alignment in segments(in clothoid for example). Then you can not pick up the polyline to origin it as alignment. You have to reenter all the geometrical information manually . . .

  3. Joe McManemin says:

    How do you fillet/chamfer a polyline segment?

  4. Steve – Most of the alignment that I needed to tweak last were lwpoly-converted – part of a corridor etc making a redefinition difficult.

    Tryfon – I would only export a copy of the drawing down to basic entities on an as-needed basis. Take a look at the weeding and curve tools on the featureline toolbar to help you reconvert a highly-segmented polyline into a simpler entity.

    Matthew Anderson

  5. John Mayo, PE says:

    I have been doing this for some time and I have noticed it failing once in a while (draging the manipulates the curve). When it happens I just delete the curve, drag the tangents to the PI & the join back up automatically.

    If I place a new curve the tangent line appear & stay put.

    If you don’t have a copy of the pline, just offset the alignment by 1 unit and then one unit back. The offset command will create the pline.

    Joe the fillet command does work on a pline. If you want a non zero radius just select two cojoined segments during the commnad. If you want to remove a curve with a zero radius, select the two tangents on eith end of a cuver segment.

  6. Steve Boon says:

    Matt’s original post and my earlier comment describes a process for creating a new alignment and then editing it so that the tangents are visible and the PI points are selectable.

    If you already have an alignment that is being used for something then John’s offset method works well. If you start the fillet command with the radius set to zero and then select the polyline option you can remove all of the curves from one copy of the polyline, and leave the other one to provide snap points for grip editing the curves back to their original radius.

  7. Joe McManemin says:

    I meant to say “a polyline arc segment”.

  8. Edson Silva says:

    In Civl 3D 2009 this don’t happen…

  9. Edson –

    I used 2009 Update 1 to generate these images. A polyline arc segment can be fillet’ed out with a fillet radius of 0 and selecting the two tangents on either side of the arc.

    Matthew Anderson

  10. Edson Silva says:

    Forgiveness for my english, Matthew. I’m from Brazil.

    I wanted to say: the tangents and PI are NOT missing in my drawing.
    Convert a polyline object into an alignment works for me.
    I used AutoCAD Civil 3D 2009 British Version 2.
    Thank you for responding.

    Edson Silva