Civil 3D Horizontal Control

Tags alignment, segment, segment types, design control, horizontal control, dynamic model

This larger topic of Civil 3D Alignments is a serial and long-term effort. Are there other forms of horizontal control inside of AutoCAD Civil 3D? You bet. For example: the features and tools in Civil 3D Survey are all about the survey and point based side of that. Survey is not something to ignore even if you only do civil engineering design. Are not your points and lines related?

Know All the Tools

You’ll find the make or edit it like an alignment approach everywhere in C3D. Go ahead edit a Feature line, a Parcel segment, and this list goes on and on. Let’s confine ourselves to the horizontal control linear features. I can’t promise we’ll trap ourselves to purely linear thinking about Alignments. That would be a waste of useful tools and your 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 make 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 parts separated in space. At times that is really useful from a design perspective. If you know this, you can build the Frame of a 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 it’s confusing, it is really useful to move around the segment Buckets.

We start at the beginning of horizontal control (HC). Every Alignment has a mission critical reference point and collected Stationed segments of various Kinds. Civil 3D refers to the kinds of segments as Types too. Then there are the formal segment types as well – as in Fixed, Float, and Free. Types of types of types? Arrrgh.

Civil 3D assumes we already understand tangents are not curves and the Rule based differences in the managed control of each Type of Alignment. In Civil 3D interface similarity, uniformity, and OOP programmer speak supplant any normal form of semantic accuracy.

Is That Semantic Speak?

Civil 3D is also careful not to call the Alignment’s reference point the “start” point. It isn’t. It may be the case the reference point is the start point. This is particularly true if you Create By Object. A reference point at the beginning is not necessary or even what you really need. Call it an illusion fashioned upon our old habit.

Create by Object isn’t really faster than the Create by Segment methods. You have much less design control with point dependent or Fixed segments. Thankfully, these days Civil 3D is much friendlier about changing Constraints and segment Parameters to get around some design construction issues.

It can be really 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 the Alignment if we need to. 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 Intersections points and create specific segment geometry constraints in between them.

The segment reversal tool’s called Reverse Sub-entity Direction in the Alignment Layout toolbar. Segment reversal and/or reference point relocation may indeed be the only way to construct some of the HC you need. That’s why the 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. May I suggest some off project practice is well worth the effort. That’s one reason why we supply lots of examples with our Production Solution products. You get a deep Civil 3D Sandbox with solid feedback Styles.

Reference Stationing is Temporary

When we move around the Alignment reference point and/or change the Stationing we get warnings from AutoCAD 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. Less depends on this in the more current versions of Civil 3D. Alignment creation and editing improved a lot with the advent of Geometry locking.
When we’re doing the initial design or survey HC work, a change to the reference point or Stationing is not very significant. At this point the labels we put on the Alignments are QA. Are my segments connected? Are they are only there to let us know we’ve connected up the segments correctly? Nah. See there you go again trying to get ready to publish stuff before it’s time.

An Alignment in Reverse

Reversing the entire alignment is different from moving the reference point. This is not the same things as reversing a segment either. Alignment reversal has more violent consequences. Station Properties related to the Design Rules, Supers and Intersections get wacked as they employ the Stationing at time A. Is this just a fast way to rid that alignment of bogus Design Speed data?

“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.”

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

The last bit of the warning recognizes you must pay attention if you have Networks that reference the Alignment(s). If we’re building and not editing established and referenced HC, we can ignore it.

Alignment Segment Tools

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

Then again 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 in the math in the model. Not exactly the same thing. 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 or the 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 HC and VC designers use all these Civil 3D 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?

The Alignment Management posts: a study guide to Read and Test in AutoCAD Civil 3D.

Civil 3D Alignment | Civil 3D Alignment Types | An Alignment in Civil 3D | Baseline Civil 3D Alignments | The Alignment End View in Civil 3D | Annotative Profiles in Civil 3D | Civil 3D Horizontal Control | Alignment Based Point Groups

Alignment Video posts: (see the Deliverables course in the Members section)

Civil 3D Alignment Matters - An Overview | Civil 3D Best Fits are Fast and Better | Civil 3D Best Fit Segment Tools