Civil 3D Horizontal Control

Tags alignment, alignment type, feature line, horizontal control, vertical control, Project Management, reference point, station, segment types

Any exhaustive discussion about the large topic of the Alignment in Autodesk Civil 3D is a serial and long-term effort. Even the familiar fundamentals of civil engineering Horizontal Control are nuanced for this one of many roles for the Civil 3D Design Control Manager. We certainly need to align our thinking with the Civil 3D functional and workflow mechanics.

Folks ask, “Why did Autodesk make the simple Alignment so complicated in Civil 3D? You can draw the thing with AutoCAD stuff in half the time.”
That may not be true for those with other distinct Civil 3D skill sets.

This post remains a work in progress. Significant updates and changes have been made to the original.

Horizontal Control in Civil 3D

For the most part our chief Civil 3D design and deliverables production delivery problems do not revolve around Horizontal Control construction.

The more substantive design production and publication concerns are about the managed and the malleable in the design and maintenance of the many dynamic models that the Alignment Horizontal Control Manager enables inside Civil 3D. These other Alignment capabilities AutoCAD primitives can never deliver.

Are there other forms of Horizontal Control available inside of AutoCAD Civil 3D? You bet. For example: the features and tools in Civil 3D Survey are all about the Survey Figures and Point based side of that. Survey is not something to ignore even if you only do civil engineering design. Maybe we figure out that our points and lines are related?

The Civil 3D Feature Line is another often preferred favorite to produce civil site design control in Civil 3D. Horizontal and Vertical design control wrapped into a single Feature can indeed be very useful. You may be a member of the large Feature Lines Only crowd. The Design by Breakline method and practice focused on Surface construction has been a mainstay for a long time in Autodesk Civil Land.

Linear design control works. Can we make it work better?

The Man in Me must ask,
“Do you want to manage lots of separate and independent Feature Lines in a drawing or manage related Feature Lines across many project drawings?”
Your call.

Dude. The obscure Dylan references to the The Big Lebowski, the New Morning album, and 17-year cicadas are intentional. There is a certain timey poetry in that.

Know All the Tools

Everywhere in Civil 3D, we find the create, edit, and manage it like an Alignment approach. Do we get the message? Maybe we are annoyed?

Go ahead edit a Feature line or a Parcel segment. This list goes on and on.
For the moment let’s confine ourselves to the Horizontal Control linear Features.

We cannot trap ourselves into purely linear thinking about Alignments. That would be a waste of the useful tools and our time. It would cloud both our judgement and understanding. Each Type of Alignment has a distinct form of managed control. Recall an Alignment is really a…

Bucket of Buckets

We can easily create an Alignment that contains nothing. Beginners often do this accidently in Civil 3D. We can make Alignments with disconnected segments too. These are Alignments with their parts separated in space. At times that is really useful from a design process perspective.

If we know this, we can build the frame of a design solution before you create the detail. We can make segments that go in different directions – the segments may look connected when displayed but are not. Although this may be confusing, it can also be really useful to move around, massage, and reconnect the Alignment segment buckets.

Perhaps if we think of Alignments in Civil 3D as data warehouses to hold and manage buckets of design control, things work out a bit better?

Types of Types

Shall we start at the beginning of Horizontal Control (HC)?
Every Alignment has a mission critical Reference Point and then collects stationed segments of various Kinds. Civil 3D refers to the kinds of segments (tangents, curves, and spirals) as types too. Then there are the formal Segment Types as well – as in Fixed, Float, and Free. Types of types of types? Arrrgh.

Is That Semantic Speak?

Civil 3D assumes we already understand that tangents are not curves or spirals and the Rule-based differences in the managed control of each Type of Alignment.
See the Civil 3D Alignment Types post.
In Civil 3D interface similarity, uniformity, and OOP programmer speak supplant any rational forms of semantic accuracy.

Alignment Reference Points and Station Values

Civil 3D is careful not to call the Alignment’s Reference Point the “start” point - Because It isn’t. The Reference Point property is found in the Stationing tab of the Alignment Property dialog box.

It may be the case that the Reference Point is the resolved first segment start point. This tends to be particularly true if we regularly employ the Create By Objects tool. A Reference Point at the beginning is not necessary or even what we really need. Call it an illusion fashioned from our work habits.

Create by Objects isn’t really faster than the Create by Segment Layout Tool methods. We have much less design control with point dependent or Fixed segments. Thankfully, these days Civil 3D is much friendlier about allowing us to edit and change the Constraints and segment Parameters to get around some common Horizontal Control design construction issues.

Technically, the Alignment Reference Point and the assigned Station value are not confined to locations on the Alignment or any of its collected and managed segments at all. This can be more than a bit disconcerting. The Reference Point and Station properties do create a mission critical relationship within the Alignment.

It can be useful to employ the Reference Point property tool differently. We can reference the segments and the related Stationing from the middle or any point on or off the Alignment if we need to.

Unrelated Alignments may share the same Reference Point and/or Station property value. This can be really handy to sync some forms of our Alignment based annotation.

A design from the middle technique combined with Segment Reversal comes in pretty handy should you want to build roadways and other Corridors using key Intersection points and create specific segment geometry constraints in between them.

Reference Stationing is Temporary

When we move around the Alignment Reference Point and/or change the Station property value we get warnings from Civil 3D that our changes will affect other things.

“Warning! Changing the reference point location or the reference station value may adversely affect objects and data already created from the alignment.”

Looks scary. We need to recognize what is really attached and/or dependent on the Alignment Stationing or the Horizontal Control geometry points. Less depends on station properties in the more recent versions of Civil 3D.

Alignment creation and dynamic editing improved a lot with the advent of Geometry locks to Alignment’s critical geometry pointsfor the many children of Alignments.

When we’re doing the initial design or survey Horizontal Control work, a change to the Reference Point and/or Stationing may not be very significant. At that point, the labels we put on the Alignments are often QAQC related.
Are the Alignment segments collected and connected properly?

Are the Alignment Group Labels there only there to let us know we’ve connected up the segments correctly?
Nope. See there we go again trying to get ready to publish the model before its time.

Alignment Direction in Reverse

Reversing the entire Alignment is again different from moving the Reference Point. This is not the same thing as reversing an Alignment Segment either. Alignment reversal has more violent consequences. Station Properties related to the Design Rules, Superelevation properties, and Intersections get wacked as they employ the Stationing established at time A.

“Warning. Reversing the alignment will remove all station equations, design speeds, superelevation data, dynamic offset and curb return alignments, and may adversely affect objects and data already created from the alignment.”

Is the Alignment Reversal tool just a quick way to wipe that Alignment of now bogus Design Speed and/or other Alignment data behind? Yes and no.

Alignment Reversal and Alignment Children

In general, basic and yet still dynamic Offset Alignments without Widenings survive most fully connected Alignment reversals thanks to the default Geometry locking behaviors and Constraints.
This is good news. We should still check the Offset children after.
We may lose Constraints and end up with only geometry point dependent segments if you play the reversal game a lot.
Destruction and recreation of child Offsets always works.

The last bit of the reversal warning recognizes we must pay attention if we have Network Features that reference the Alignment(s) or its children.

We must regularly remind ourselves that our method and practice to share our Alignment-based design control should be project-based and not drawing centric.

If we’re building and not editing established and Referenced Horizontal Control, we can ignore the warnings.

Segment Direction Reversals

The Alignment Segment reversal tool is called Reverse Sub-entity Direction in the Alignment Layout toolbar. Civil 3D reasonably protects us from reversing individual previously connected Segments.
Segment reversal and/or Reference Point relocation may indeed be the only way to construct some of the Horizontal Control we need. Why these Alignment key properties are in there.

To do this well requires experience with Civil 3D’s Alignment Edit tools and familiarity with the Segment Types, Constraints, and Parameters. Off project practice of Alignment construction and editing is well worth the effort.
Another important reason why we supply lots of examples with our Framework for Civil 3D Jump Kit products. We deliver a deep Civil 3D Sandbox Project data set with vast collection of adaptive Style tools to play with.

Alignment Segment Tools

Civil 3D newbies often think the names of Alignment and Profile Segment Types are a bit weird, confusing, or maybe even backwards. Can’t say that I blame them.

I love to point out…

We do not draw Alignments, Profiles, and even Parcels in Civil 3D.

What? No way, Dude.”

We define the properties and conditions to resolve the math (the data behind) in the model. This is not the same thing as draw.

The real point being the Segment Type names: Fixed, Float, and Free relate to the definition geometry points used in the Parameter constraints applied in the math. They do not point to the representation - the current resolved picture of the linework.

Look carefully at the Layout toolbar menus and this should be clear.

  • Fixed – fixed point definitions
  • Float – attached at one end definitions
  • Free – attached at both ends definitions

Good Horizontal and Vertical Control designers use all these Segment Types.
Design masters may often change between them frequently to get from here to where they want to go. They may go backwards to go forward with a better set of design constraints.

Are We There Yet?

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