Alignments: Parents, Children and Grandchildren

In the 2010 release of Civil 3D Autodesk unveiled a new type of alignment: the offset alignment.  Originally created for the intersection tool, these alignments can be created manually by the user to fill a whole host of functions for design.

Offset alignments need a parent alignment to take their position.  As you need to edit the parent alignment’s position the offset alignments will update, staying generally parallel to their parent.  Keep in mind, you can create widening regions that shift the offset alignments so they do not have to be absolutely parallel to the parent alignment, but these regions will stay relative to the parent.

If the original alignment is the parent, and the offset alignments are the children, you can then create “grandchildren” alignments that are offset from the children.  Now we have several layers of control throughout the design.  If the overall road centerline (the parent) alignment needs to shift, all of the alignments move in relation.  If the parent stays still but one of the children needs to shift over (for a lane moving over) then the grandchildren shift with it as well.  Finally, if the edges of the roadway need to shift, but the overall boulevard centerline and the lane centerlines are staying still, you still have that level of control.

That example is of a fairly complex boulevard design.  But there are other reasons offset alignments can be useful.  If you are working with parcels, they also respond to alignments.  The issue up until now has been that if the roadway centerline that controls the right-of-way (ROW) parcel frontage moves, the ROW parcel doesn’t necessarily update with it.  If you instead use the offset alignments to control the ROW parcel, then the centerline alignment moves, the ROW alignments move, and the parcel appropriately updates.

This is all towards a level of control that we didn’t have before.  Changes in real-time, and keeping things relative.  This will keep your designs moving forward through the revision cycle.