Alignments in AutoCAD Civil 3D do have types. So? No biggie. If you get this wrong when you create the Alignment, you can change this? Errr. Well sort of and it depends. Remember an Alignment is a collector of Properties. Different types of Alignments have different properties. As I said last post we might think of Alignment types as “purposes”, but we only create confusion if we think that way.
Alignment types are really about forms of managed design control - a somewhat subtle but significant difference in perspective.
Dumb and Dumber
Types are all about the Alignment’s property buckets. Yes, Style is one of them. The property buckets are reflected in the tabs we see in the Alignment Properties box. The contents of these are more important than what you draw or what you see on the screen. In Civil 3D it’s about the data, Baby. Actually, Dude or Dudette, it’s about the managed design control of the data.
“Honey, I know your type.”
Centerline Alignments are the most frequent choice we make. The Centerline type allows us to employ Design Criteria (aka rules) to all the geometry collected in the Alignment’s property buckets. The management tools of Design Criteria requires a Design Speed property to turn DC on. Be careful - you can delete the Design Speed after the fact. The diva that is Civil 3D will squeal at you later.
The Miscellaneous Alignment type is dumber – no Design Criteria properties rules can be added or applied to the collected data. Everything else stays the same. Yeah.
You can work without the rules.
If you create an Alignment as Centerline add some DC and change the type to Miscellaneous, the Alignment keeps the Design Criteria properties, but hides them. The Alignment doesn’t forget. As a Misc type the DC no longer manages the math relationships. If you change the type back again, the diva may scream.
The Rail Alignment type has it’s own Design Criteria and Track width coupled with Design Speed.
The Offset Alignment type is connected at birth to Centerline, Miscellaneous, Rail, or other Offset Alignment type Alignments. The Offset Alignment type is a hierarchical property. If you change the Alignment type, you destroy the relationship. Undo or reconstruction is the only way back. You can, of course, type an Alignment this way to keep track for it by “purpose”. That will probably confuse you and others later. Planned Names work better.
The Curb Return Alignment type is a link property. The control connects to separate Alignments together. The Civil 3D Intersection wizard creates these. You can, of course, type an Alignment this way to keep track for it by “purpose”. That will probably confuse you and others later. Planned Names work better.
The Common Dumbest
Last post we talked about four steps we need to accept about Alignment Features in Civil 3D. Before we ever enter the Alignment Create box we need to consider something else – old CAD habits. If you create Alignments from Objects you restrict significantly what you can do with an Alignment. CAD primitives are dumb. They obey no rules. To create an Alignment with the Alignment Layout tools takes only a little longer. To religiously employ the Layout tools significantly increases your design control capabilities and your Civil 3D skill.
Put another way – an Alignment in Civil 3D doesn’t need to be all connected all the time. Pieces can be going in different directions from time to time. Sorry. You cannot do that with a polyline.
The other bad CAD habit is not separating your design control from the results. We do this. There’s nothing particularly hard about fixing the problem and employing Civil 3D Data References more effectively. See the videos.
Design By Intersection
I believe Intersections are one of the best and most misunderstood tools for building better horizontal control inside AutoCAD Civil 3D. Think about it. Often we are concerned about the points of connection. The stuff in the middle is easier if we solve these first. What does the tool do? First it builds flexible interconnected offset horizontal control between two alignments.
The 3 step Intersection wizard is not an all or nothing tool. Do only the Horizontal control. Stop on page two. Connect up the right pieces and clean up the unneeded. Intersections require that you understand Offset Alignments, Alignment Widenings, and Curb Return Alignments and the various edit interfaces to manage and maintain them.
The Book of Alignments Posts
A study guide to Read and Test in Civil 3D
Updates to this post series are on-going.