Cadalyst Labs Review: Autodesk Civil 3D-Model-Based Civil Design Improves Efficiency

1 Mar, 2005 By: Cadalyst Staff

An innovative, object-oriented approach to civil design.

Civil Engineering Professionals looking for a glimpse of the future would be wise to brush up on one key topic: intelligent objects. Just as architectural CAD software has largely abandoned generic CAD entities such as lines, arcs and polygons in favor of intelligent objects such as doors, windows and walls, civil CAD appears headed in a similar direction, at least if Autodesk has anything to say about it. Autodesk's Civil 3D 2005 makes unprecedented use of objects in a quest for a more model-based design environment where on-screen entities also maintain key relationships with design data. The new approach may present an unwelcome learning curve for some users, but the possibilities for more integrated, efficient design might be well worth the effort.

People unfamiliar with Civil 3D often ask if this is an upgrade to Autodesk's Land Desktop. The answer is a resounding "No." Civil 3D is a new product (officially released in 2004), with some of the same capabilities as Land Desktop, but with a new approach to designing roads, residential subdivisions, building sites and other land development projects. Users can exchange data with Land Desktop and may find reasons to move projects from Land Desktop to Civil 3D, but may also find reasons to use the two products in tandem—more on this later. Like Land Desktop, Civil 3D is built on top of AutoCAD, so the interface will be familiar to AutoCAD and Land Desktop users (figure 1).

 Figure 1. Civil 3D presents a familiar AutoCAD-based interface.
Figure 1. Civil 3D presents a familiar AutoCAD-based interface.

Objects of Affection

In the Civil 3D world, an object is a drawing element that can maintain a relationship with another object. For example, an alignment object is a combination of lines and curves that collectively defines the location of a project component, such as the centerline of a road. An alignment can be a stand-alone object or the parent object of other objects such as profiles and cross-sections. If you edit an alignment, the changes are automatically reflected in all related objects. Other key Civil 3D objects include points, surfaces, sites, parcels, gradings, corridors, assemblies and subassemblies. The objects have designated hierarchies that display in a handy new interface component called Toolspace (figure 2).
Figure 2. The Toolspace displays objects in use and their settings.
Figure 2. The Toolspace displays objects in use and their settings.

Land Desktop previously employed objects to a limited extent, but Civil 3D takes a more comprehensive approach. For example, where Land Desktop uses a contour object to represent individual contours in a topographic model, Civil 3D uses the surface object, which encompasses the entire terrain model, including points, contours, breaklines and boundaries. If users edit a surface point either graphically or by editing text, the surface object updates immediately. There's no need to rebuild the terrain model after every edit.

Autodesk civil 3d
Autodesk civil 3d

The dynamic updating capability also shines with the parcel object, which represents real estate parcels such as lots in a subdivision. Civil 3D includes a variety of tools to subdivide tracts of land into parcels with predefined areas. Parcels can be punched out quickly in cookie-cutter fashion or individually in irregular-shaped areas using interactive tools (figure 3). Once in place, parcel lines can easily be moved, with all affected parcels updated automatically.

Figure 3. The parcel object allows tracts of land (top) to be subdivided into equally sized lots (bottom).
Figure 3. The parcel object allows tracts of land (top) to be subdivided into equally sized lots (bottom).

Road designers will find plenty of tools, too. In addition to offering numerous ways to create alignments, Civil 3D enables painless updating of alignment data and related objects when an alignment is changed. For example, when an alignment is shifted graphically, its stationing, curve data and other labels update automatically. Profile data is also updated automatically when an alignment changes, so users don't have to go through tedious processes such as cutting new ground lines. Finished profiles may require some manual tweaking after an alignment change, but the overall effort needed is reduced dramatically from previous approaches.

Civil 3D's corridor object provides a new approach for modeling highway and railway projects. Linking various other objects, including alignments, surfaces, profiles, assemblies and subassemblies, corridors are created along one or more baseline alignments by placing a cross-sectional assembly at incremental locations and by creating slopes that reach a surface model at each incremental location. Each assembly is composed of subassemblies, such as curb and gutter, pavement, sidewalks, ditches and other elements. Civil 3D provides a wealth of prebuilt subassemblies (figure 4) that can be inserted into an assembly for quick creation of complex sections.

Figure 4. Prebuilt subassemblies (left) can be used to build corridor models (right).
Figure 4. Prebuilt subassemblies (left) can be used to build corridor models (right).

When changes are made to a corridor or one of its component objects, the corridor can be either automatically or manually updated, depending on the user's settings. Corridors are also useful for generating cross-sections, earthwork volume reports and 3D renderings (figure 5).

Figure 5. Corridors can be used to develop 3D renderings of roadway projects.
Figure 5. Corridors can be used to develop 3D renderings of roadway projects.

Another concept crucial to understanding Civil 3D is the use of styles, which control the display and design characteristics of objects, such as color, linetype, fonts and so on. Each Civil 3D object has a standard style that can be used as is or as the basis for building new styles. If users want to customize some attributes of a style, they can create a new style or make changes to an existing style and save it.

Whither Land Desktop?

Even with all its new capabilities, Civil 3D doesn't do everything Land Desktop does. Civil 3D doesn't include pipes or hydraulics modules, so storm drainage and sewer design still must be done with tools such as Autodesk's Civil Design, which is available only as a component of the Civil 3D Professional package. Civil 3D also has no survey capabilities, so users will need an alternate approach such as Land Desktop with Autodesk Survey to move survey data to and from the field. In addition, Land Desktop still handles plan production better.

For new projects and ongoing projects that are likely to experience numerous design iterations, Civil 3D's object-based capabilities become more attractive. Civil 3D includes tools to import and export Land Desktop project data so the products can be used together. The import utility works reasonably well, although not seamlessly. Land Desktop data is stored in a project-based system and Civil 3D data is stored within the drawing, so not all data comes through in one fell swoop. For example, points from a Land Desktop point file require a separate import process. On the whole, Civil 3D's drawing-based data storage is a big improvement, because virtually all project data is accessible from the drawing, not in external files.

To export Civil 3D data to Land Desktop and other environments, users have several options. In Land Desktop 2005, Civil 3D data can be extracted and imported directly for use in the Land Desktop environment. Also, an object enabler for Land Desktop 2005 and other AutoCAD 2005-based products allows users to open Civil 3D drawings and interact with Civil 3D objects to a limited extent. For older versions of Land Desktop, users can export Civil 3D data to LandXML format and then import the LandXML data into Land Desktop. Civil 3D also includes the ability to save a drawing file to older versions of AutoCAD and convert Civil 3D objects into native AutoCAD objects.

Bells and Whistles

With its model-based design, Civil 3D is loaded with cool features and new ways to extract data, such as through tool tips, the little boxes that pop up when the cursor is strategically positioned. For example, users can place the cursor anywhere within the limits of a surface and determine a 3D location in station-offset format (figure 6).
Figure 6. Tool tips provide instantaneous 3D location information based on the position of the cursor.
Figure 6. Tool tips provide instantaneous 3D location information based on the position of the cursor.

Long-time AutoCAD and Land Desktop users might need to rethink how they query a drawing for certain information. Don't expect to select a portion of an alignment and determine its length with AutoCAD's List command. When you select any portion of an alignment object, the entire object is highlighted. To get information about it, view its properties in one of Civil 3D's many tabular formats.

The on-the-fly editing of objects is impressive, although as with any software tool, a dose of caution is warranted. Imagine the easy grip editing of surface models placed in the hands of an inexperienced user and the possible ramifications. Likewise, the grading commands let users create a proposed surface that is precisely draped over another surface, creating a grade break everywhere the proposed surface crosses the edge of a triangle in the TIN (triangulated irregular network) of an existing surface. Again, a neat feature, but an inexperienced designer might use this to design a 200' X 200' parking lot with seven or eight grade breaks in each direction, much to the chagrin of a surveyor or contractor stuck building an overly complex design.

But these are relatively minor concerns in a generally impressive product, especially one rolled out barely a year ago. The documentation appears solid, with just a few minor discrepancies between the Help system and the current software, again probably due to the relative newness of the software. Some stability problems have been reported, particularly with the grading object, but Autodesk addressed many of these in a service pack released in late 2004. As with other AutoCAD-based products, Civil 3D is highly customizable. The object model is exposed to programmers working in languages such as VBA, .NET and Visual LISP, although the degree of exposure is another area that is still maturing.

Civil 3D 2006, due for release in the spring of 2005, reportedly includes pipe layout and drafting tools, enhanced corridor modeling and section editing, expanded reference support that allows multiple users to share project data simultaneously, and improved stability.

The key question now is how swiftly the civil profession will latch onto a still-evolving Civil 3D. Will the object-based approach become the backbone of future Autodesk civil products and reshape how civil engineers approach CAD? Autodesk thinks so, and it may be time to hop on the train.

Andrew G. Roe is a registered civil engineer and president of AGR Associates. He is also author of Using Visual Basic with AutoCAD, published by Autodesk Press ( E-mail him at

About the Author: Cadalyst Staff

Cadalyst Staff

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