| Jan 17, 2013
The last Parcel post we met the AutoCAD Civil 3D Site Parcel’s planar nodal topology engine. This is a model somewhat like the surface model we know all too well. The familiar surface TIN eats point data (x,y,z locations) and it’s triangle edges are edited and forced by breakline data (x,y,z pairs).
The Parcel topology model plays by another set of rules that are eerily similar to the TIN for a very good reason. We may want the Parcel model’s input geometry for use as surface model data. The Grading work for the Site Parcel complements its Parcel design and construction work and vice versa.
Can One Plus One Be More Than Two?
The Parcel Posts - a study guide to Read and Test in AutoCAD Civil 3D
Site Parcel Essentials – Part 1 | It’s Not Yo’ Daddy’s Parcel – Part 2 | To Edit Parcels is to Create? – Part 3 | Parcels Have Priorities - Part 4 | A Strange Universe of Parcel Inverses and Mapchecks – Part 5 | Dances with Parcels – Part 6 | Pack Dances with Parcels – Part 7 | Cycle Manipulations of Segments – Part 8 | Select Manipulations of Segments – Part 9 | Visual Manipulations and Many Segments – Part 10 | Site Parcel Alignment – Part 11
We discovered in the last post that a Parcel Segment is not exactly the same as the geometry we initially fed into the engine. It is processed and prepared data. If we view the AutoCAD Properties of a Parcel Segment in the AutoCAD Properties box, you’ll note there is no exposed Geometry section for a Parcel Segment Feature. A Feature Line’s AutoCAD Properties are barely better, but there we do get more viewable Data.
To Change a Parcel Segment
We must employ the Parcel Segment editing tools that are available in the Parcel Segment Ribbon to get at the underlying geometry. The Parcel Segment Ribbon includes both Geometry (Horizontal) and Elevation (Vertical) edit panels. These panels look like somewhat simplified versions of the similar panels on the Alignment Ribbon. They look a lot like dumbed down versions of the Feature Line Ribbon’s Geometry and Elevation panels as well. Did I mention the Figure Ribbon?
Perhaps there’s a reason for this similarity beyond the obvious?
In the Parcel Segment Ribbon’s Geometry panel we can add and remove PIs (these become the nodes we talked about last time). We can make some basic changes to tangent and curve segments. We may also join single segments into large multi-segment ones, break up multi-segment input, and even flip the direction of segments. Yes, in the Civil 3D world Parcel Segment direction can matter. See this post for some more critical details about Direction in Civil 3D.
The Parcel Layout Toolbar is modal (always available) so we can also create individual Parcel Segments and/or groups of tangent Parcel Segments to create new resolved Parcels interactively. We’ll talk more on the Parcel Layout Toolbar in a later post.
What Do We Edit?
Although it may appear that way, we are NOT really and cannot directly edit the Site Parcel topology itself.
The Site Parcel topology and all its output are ALWAYS resolved. It is a dynamic model, and we don’t have Rebuild control. We edit the input. The model collects data, processes it, and produces a result. The three parts are separate things just like in a surface model. Really? Really.
Here’s the easterly Parcel Segment (as shown above) in the Parcel Elevation Edit tool.
Note the two intersection nodes are displayed differently. Note the node elevation of one node is actually at zero. It’s derived from the southerly west to east Parcel Segment.
The Site Parcel topology employs 2D or planar behavior.
It’s Apparent (pun intended here) that the linear objects contained in the Parcel Segments certainly do not intersect in the 3D world.
This arrangement of “3D” tangent segments still resolves into a Parcel in the planar-based topology.
The Parcel Segment input data also preserves the Elevation data derived from the original linear geometry. The Parcel Segments, therefore:
- May be employed in Gradings within the Site as source data and
- Parcel Segment input is acceptable as Breakline input into ANY surface model
Yes, you read that correctly.
You can get an editable dynamic rough surface from Parcel Segments. The Parcel duality is a cool trick. Duality can be a bit confusing.
Of course, you can’t edit the Elevation properties of the intersection nodes in this selected Parcel Segment.
You have to edit those input geometry locations in the other separate Parcel Segments. We’ll discover when we talk about Slide and Swing tool connected segments, this constraint may not be so bad either.
Wishes with Questions
What happens if the geometry points do match vertically? In the Parcel Segment’s Elevation Editor are we editing both geometry locations on two Parcel Segments at the same time? Not so obviously - Not.
Perhaps it would be nice if Civil 3D would let us hop over to these other Segments from here in the Elevation Editor. Maybe that Parcel Segment selection change functionality (that could be here) was deemed to be too confusing to us Civil 3D users?
There is more at issue.
Inside the Site Parcel other Civil 3D Features may participate. What if that nodal segment information we see here came from a Survey Figure or an Alignment? Oh Dear.
If the Parcel Segment Ribbon told us the Parcel Segment’s Site, that might be useful. You get that info from the AutoCAD Properties box in any case. The Site property is “exposed” for all Site collected Features.
We must pay attention to the entire available Civil 3D interface to create, edit, and manage Parcels.
Do we focus on the whole or the parts? We must switch our focus between both.
A Feature Line Sameness?
Here’s the Elevation Editor for a Feature Line in a different Site. This two tangent segment Feature Line crosses 3 different Alignments two times with a Grade Break between. Visualize this Feature Line as a “V” that crosses a road.
Why would he do that?
Why would the Feature Line cross the road? - To get to the other side.
Civil 3D Feature Line Features manifest some of the same nodal interface 3D edit behaviors as Parcel Segments. In other words, the Site Parcels’ nodal topology is used to “discover” and make visible the nodes at all the Site Parcel shared Segment intersections.
Big Whoopee. This is somewhat useful information. How can we act on it?
There’s More - Way More
Maybe we’ll dig into the following brief remarks in depth in a later post but for now…
Civil 3D supports dynamic Feature Lines these days:
- You can either employ a Feature Line linked to Alignment/Profile pairs or
- The truly wonderful and terrifying prospect of linked Feature Lines from a Corridor model.
Maybe you expected there was no way to get all that fancy horizontal control (with tangency constraints) and vertical control (including vertical curves) built into a dumb Feature Line.
They are not so dumb really. Maybe that dumber Parcel Segment Ribbon was trying to hint at something.
It goes without saying, that to resolve those potential kinds of interactive grading complexities the Feature Lines collector in a Site has Style-based Priorities of its own. What pays attention to that?
Did the lights go on? I certainly hope so.
Dear, maybe those are headlights?
I wouldn’t want you to work too hard because you expect "Feature Line" is a new word for an old school breakline.
No such luck.
At the top of the post we asked the question, “To Edit a Parcel is to Create?”
My contrived post title intentionally left off a final word – “What”.
To Edit a Parcel is to Create What?
Now that we understand a bit more of what the Site Parcel chain saw is up to, next time we can explore the Site Parcel collectors other priorities a bit deeper.