Use an assembly object to create the structure for a corridor section.
An assembly is a AutoCAD Civil 3D drawing object (AECCAssembly) that manages a collection of subassembly objects. Together, assemblies and subassemblies function as the basic building blocks of a roadway or other alignment-based design. An assembly object must be applied along an alignment to form a corridor, and it can reference one or more offsets.
An assembly object, like its corridor and subassembly counterparts, can adapt to conditions such as superelevation and cut or fill requirements.
The following components comprise an assembly object:
- Insertion Point. This is the initial point in the drawing that is selected to create the assembly object. It corresponds to the centerline of the eventual corridor object. This is also known as the ground reference point and typically follows an alignment as well as a design profile (vertical alignment).
- Baseline. The baseline of an assembly typically displays as a visual aid (marker) representing a vertical axis at the assembly baseline point. If you want to attach a subassembly to the baseline point, you can do so by selecting the baseline marker. This method of attaching subassemblies to an assembly is sometimes easier than selecting the baseline point, especially when there are already one or more subassemblies attached at that point.
- Baseline Point. This is a point on the assembly typically representing the start point of the first subassembly that is attached to the assembly near the controlling alignment. By default, the baseline point coincides with the insertion point and therefore follows the centerline alignment and profile. If you want to begin sectional elements oriented away (horizontally and vertically) from the centerline, do so by moving this baseline point away from the assembly insertion point.
- Offset Line. The offset line is a typically vertical line visually representing a vertical axis at the offset point. If you want to attach a subassembly at an offset point, you can do so by selecting the offset line marker instead of selecting the offset point. This method of attaching subassemblies to an assembly offset point is sometimes easier than selecting the offset point, especially when there are already one or more subassemblies attached at that point.
- Offset Point. This is a point on the assembly representing the ground reference point along an offset alignment for the eventual corridor object. Subassemblies attached at this point follow an offset alignment and its designed profile. For example, in the case of a highway with service roads on one or both sides, the service road centerlines are represented by offset points. There is always just one baseline point on an assembly, and there can be zero or many offset points on an assembly. Offset points can be added to or deleted from an assembly at any time.
To complete the definition of an assembly object, you typically add multiple subassembly objects, such as lanes, curbs, or ditches, along an alignment. Each subassembly can connect to the assembly baseline point, any assembly offset point, or to another subassembly already associated with the assembly. A subassembly can also be attached to these points with a relative offset and/or elevation from the point.
A subassembly definition references point, link, and shape codes. Points are the vertices of the subassembly, and they can be attachment points for adjacent assemblies. Links are the line segments or curves between the points. Shapes are two-dimensional polygons that represent the cross-sectional shape of the subassembly. The following figure shows a coding diagram for a Basic Curb and Gutter subassembly:
For more information, see Understanding Subassemblies.