topic Re: The concept of wall break line in Civil 3D Forum

The concept of wall break line

soonhui — Tue, 12 Jul 2022 10:20:46 GMT

Refer to this guide here. I have a few questions about the concept of wall break line and how to use it.

Let's refer to this image, taken from the above guide:

The way I understand it is that for the "defined" wall break line (as per the above image, and let's call it Line A), civil 3d will internally generate another line, parallel to the break line with an imperceptible offset, according to the "side" chosen ( let's called it Line B). And then civil 3D will build Delaunay triangulation based on the points on the "define" wall break line, and the points on its cousin internal generated line ( ie. Points on Line A and Line B). The rest of the points-- regardless of which sides of Line A they are on-- shall still remain in order to build the Delaunay triangulation. Since Civil 3D can't take points with the same {x,y} but different z values, this is the only way it can go by.

Am I right on this?

Also, for the elevation on the Line B, can I define it on absolute basis, instead of define it as an offset from Line A? In the guide it says that:

you select either the vertex elevation (Existing Vertex Elevation is the default) and the corresponding offset vertex elevation (the default is Existing Polyline Vertex) or the corresponding offset vertex elevation difference.

I have no idea what it means. Does it mean that I can define the elevation on absolute basis, or can only on difference with the reference line basis?

If you look at the API, you can't choose the mode of elevation definition, so it's even less clear how the elevation is defined on the offset line ( Line B)!

Re: The concept of wall break line

AllenJessup — Tue, 12 Jul 2022 12:29:46 GMT

It looks like you understand the concept. This might help.

From Civil 3D help on Adding a wall breakline;

Define by object vertex (Individual). Select a polyline, or line, and select the offset side. For each polyline vertex, you select either the vertex level (Existing Vertex Level is the default) and the corresponding offset vertex level (the default is Existing Polyline Vertex) or the corresponding offset vertex level difference. If a level difference option is selected, the difference value is the default for each subsequent vertex.
Define by object (All). Select a polyline, or line object, and select the offset side. Then, enter the difference level to be applied for all offset vertices.

This might also help

https://help.autodesk.com/view//CIV3D/2022/ENU/?guid=GUID-2DB9FC3A-4D9B-483E-8FB6-431CEEE37B2A

I don't use wall breaklines often since I'm usually dealing with existing Surfaces and both Top and Bottom are shot.

Re: The concept of wall break line

Joe-Bouza — Tue, 12 Jul 2022 21:04:55 GMT

Or use an alignment and profile the top / bottom and run a corridor link

Re: The concept of wall break line

rl_jackson — Wed, 13 Jul 2022 00:51:28 GMT

@soonhui

Personally, since using C3D for 15+ years, I don't even use that sort of breakline for existing surfaces anymore. I'll use my survey figure or a featureline, and do stepped offset to replicate wall breaklines like retaining walls. If it's truly a wall like a wall for a building I'm going to use the building as a hide boundary so there's no need for a wall breakline. I don't even think I used those in LDD often as they never seemed to achieve the effect I was looking for. Just my take.

Re: The concept of wall break line

soonhui — Wed, 13 Jul 2022 03:41:09 GMT

@AllenJessup ,

It's unclear from your post ( and from the link contained in it), whether we can specify absolute elevations for vertexes on the wall breakline. Can illuminate more on this point?

Let's take a look at the link above, from both the text of explanation and the code samples, it seems that the elevation is absolute, but the explanation below from the help.

Define by object vertex (Individual). Select a polyline, or line, and select the offset side. For each polyline vertex, you select either the vertex level (Existing Vertex Level is the default) and the corresponding offset vertex level (the default is Existing Polyline Vertex) or the corresponding offset vertex level difference. If a level difference option is selected, the difference value is the default for each subsequent vertex.
Define by object (All). Select a polyline, or line object, and select the offset side. Then, enter the difference level to be applied for all offset vertices.

Seems to imply that we can only specify the offset of vertex level ( from where???).

PS: the code sample in the link refers to COM API, which is different ( again!!) from .Net API, I'll create a separate question on the API forum to seek clarification.

Re: The concept of wall break line

rl_jackson — Wed, 13 Jul 2022 03:54:33 GMT

Since you started this DTM conversation about walls, what exactly are you trying to do. Please keep in mind that a DTM (TIN) CAN NOT have a vertical face, it can only replicat this, same holds true with a corridor, there always needs to be a minute transition (i.e. not plumb).

Re: The concept of wall break line

soonhui — Wed, 13 Jul 2022 04:24:14 GMT

@Joe-Bouza , but I am creating building footprints, but Alignment and Corridors are more suited for Roads and Railway, no? Can Alignment and Corridors be made to fit building footprints?

Re: The concept of wall break line

soonhui — Wed, 13 Jul 2022 04:34:56 GMT

@rl_jackson , what I am trying to do: I want Delaunay Triangulation ( or something like TIN surface), even though the surface does contain some edges with vertical walls. If this is not achievable, I can accept the use some artificial elements to create the vertical wall, so as long as the difference is so very minute.

That's where the wall break line device comes in, for which I think is useful. Which is why I want to be able to specify the absolute vertex elevations on the wall break line ( without offset, because the concept is in reference to something else which I may be hard to access via C# API)

Re: The concept of wall break line

rl_jackson — Wed, 13 Jul 2022 04:51:58 GMT

If you need a true vertical, like a building (i.e. being plumb), a TIN/DTM cannot do that, perhaps you should look at REVIT

EDIT: You can import an the existing ground from C3D to REVIT, and if all is spatially correct could even use a Shared Point

EDIT2: There are also corridors in C3D that do create walls, but true plumb 90 is not possible in a TIN model, hence REVIT and other things.

Re: The concept of wall break line

soonhui — Wed, 13 Jul 2022 06:07:23 GMT

@rl_jackson Revit might not be suitable because I am still dealing with development sites and building footprints. In those cases, retaining wall is still needed between building footprints with different elevation.

Surface in Civil 3D should be the right concept, what would be the right concept in Revit?

That's why I said that I'm thinking about wall breakline to represent the retaining wall between building footprints with different elevation, as long as it functions in the way that I thought. Anything that I miss?

Re: The concept of wall break line

soonhui — Thu, 18 Sep 2025 03:35:32 GMT

I finally figured it out and here's my writeup.

Re: The concept of wall break line

AllenJessup — Thu, 18 Sep 2025 12:27:26 GMT

Nice write-up. Thank you for sharing.