In my overview post of alignment enhancements, I discussed alignment constraint swapping, PI index numbering, and a few new alignment labels that would take advantage of some of this new functionality. Today, we will look at some of that functionality and see how it can be utilized in the design process.
Alignment constraint swapping is being introduced to provide flexibility to users when editing horizontal alignment entities and to alleviate confusion on terminology that has been traditionally used to define entity constraint types such as fixed, free, and float.
In past releases of Civil 3D, once horizontal alignment entities were created, there was only limted flexibility given to the user to modify the entities – quite often, a user had to delete an entity and create a new one. This could prove to be quite tricky since deleting an entity really depended on how it was originally created.
What this new functionality does is give the user more control and allows you to unlock or lock parameter constraints, as well as modify the parameter constraint type of each entity and relationships between horizontal alignment entities.
First, let’s take a look at where we can set up these parameters. This is found on the alignment properties tab on the Constraint Editing tab, as shown below:
With the Lock all parameter constraints option selected, you can see that a lock symbol appears for the Parameter Constraint Lock on the alignment geometry editor:
Now, if you think this alignment geometry editor looks a bit different, let’s compare it to the alignment geometry editor for Civil 3D 2011:
At first glance, you notice the differences – the addition of three columns – Tangency Constraint, Parameter Constraint Lock, and Parameter Constraint. If you select one of the tangency constraints, you receive a pulldown that allows you to change that constraint – depending on the subentity, the options might be Not Constrained (fixed,) Constrained by Previous (floating,) Constrained by Next (floating,) or Constrained by Both Sides (Free.) Even with the Parameter Constraint Lock locked, you can still change the tangency constraint of a given entity. If you take a look at my first line, you will see that it is not constrained (fixed) and the parameter constraint is two points. I can’t change that particular constraint because it is technically not constrained by definition. However, the next entity is a curve that is constrained on both sides (free) – if I manually unlock the parameter constraint lock, then I will have an active field under the parameter constraints for that entity and I can choose what constrains it – either the radius or the passthrough point, as shown below:
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As stated earlier, this constraint swapping gives you much more control over your horizontal alignment edits.
Next, we will take a look at the new PI Label Style and how it interacts with both implied and explicit PI definitions. My rather complicated alignment is shown below, complete with some interesting looking curve extensions. This alignment contains lines, curves, and spirals, and has more than enough geometry for me to demonstrate labeling.
Before we look at the new PI labels, let’s talk about PI Index Numbering. Users have been asking for a change in the way Points of Intersection (PI) are defined for horizontal alignments, as well as an easy way to identify the mid-point of alignment curves so they can be labeled. With this release, we introduce the concept of an implied PI. An implied PI is one that is solved for, but not explicitly defined by fixed tangents. In prior releases, only an explicit PI could be labeled or reported on. However, in industry, there is normally no distinction between an implied PI and an explicit PI when staking out roadway geometry in the field. All PI information, both implied and explicit, is typically needed in a given plan set.
Previously, the Line Extension component of the alignment object style displayed fixed tangents to explicit PI locations. This component will still be available, but we have added a tangent extension component to display the extension of tangents to implied PI locations, as shown below:
In order to display the tangent extensions, the “Implied Point Of Intersection display option” must be set to one of the two display types defined. When one of these display options is selected, the tangent extension will be displayed when the alignment is selected, even if the tangent extension component visibility is off in the alignment style. The display option can be found on the Point of Intersection tab of the alignment properties dialog box, as shown below:
The new labels available will label the included angle, X-Y (or E-N for you surveyors) location, and PI index number at both explicit and implicit PI locations. Below, you can see an example of the new label style:
The new PI label style is meant to replace the existing tangent intersection label style. It should be noted that in pre-2012 Civil 3D drawings, existing tangent intersection label styles are not migrated to the new PI label style.
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