C3d Root Objects

Civil 3D Root Objects and Common Concepts

Use this skill when accessing base Civil 3D objects, working with transactions, iterating collections, or configuring settings.

Root Object Hierarchy

CivilApplication
  └── ActiveDocument (CivilDocument)
        ├── GetAlignmentIds()
        ├── GetSitelessAlignmentIds()
        ├── GetSiteIds()
        ├── GetSurfaceIds()
        ├── GetPipeNetworkIds()          ← gravity networks
        ├── GetPressurePipeNetworkIds()  ← pressure networks
        ├── CorridorCollection
        ├── CogoPoints
        ├── PointGroups
        ├── Styles (StylesRoot)
        │     ├── AlignmentStyles
        │     ├── ProfileStyles
        │     ├── ProfileViewStyles
        │     ├── SurfaceStyles
        │     ├── PipeStyles
        │     ├── StructureStyles
        │     ├── PointStyles
        │     ├── InterferenceStyles
        │     ├── AssemblyStyles
        │     ├── LinkStyles
        │     ├── ShapeStyles
        │     ├── CodeSetStyles
        │     ├── PartsListSet
        │     ├── LabelStyles (all label style roots)
        │     ├── LabelSetStyles
        │     └── ProfileViewBandSetStyles
        └── Settings (SettingsRoot)
              ├── DrawingSettings
              └── GetSettings<T>()

Accessing Application and Document

using Autodesk.Civil.ApplicationServices;

// From active document shortcut
CivilDocument doc = CivilApplication.ActiveDocument;

// From any Database (works for non-active documents too)
CivilDocument doc = CivilDocument.GetCivilDocument(database);

Note: CivilApplication does NOT inherit from AutoCAD's Application. For application-level access (open documents, main window), use Autodesk.AutoCAD.ApplicationServices.Application directly.

Transaction Pattern

All Civil 3D object reads/writes MUST be inside a Transaction:

using (Transaction ts = Application.DocumentManager.MdiActiveDocument
    .Database.TransactionManager.StartTransaction())
{
    // Read objects
    Alignment align = ts.GetObject(alignId, OpenMode.ForRead) as Alignment;

    // Write objects (must open ForWrite)
    align = ts.GetObject(alignId, OpenMode.ForWrite) as Alignment;
    align.StyleId = newStyleId;

    // MUST commit for changes to persist
    ts.Commit();
}

Best practice: Use using statement for automatic disposal. Otherwise, explicitly dispose in a finally block.

ObjectId Collections

Collections return ObjectIdCollection (not typed objects). You must cast via Transaction.GetObject():

ObjectIdCollection alignmentIds = doc.GetAlignmentIds();
foreach (ObjectId objId in alignmentIds)
{
    Alignment align = ts.GetObject(objId, OpenMode.ForRead) as Alignment;
    ed.WriteMessage("Alignment: {0}\n", align.Name);
}

Creating Styles

// Add returns ObjectId of new style
ObjectId styleId = doc.Styles.PointStyles.Add("MyStyle");
PointStyle style = ts.GetObject(styleId, OpenMode.ForWrite) as PointStyle;
style.Elevation = 114.6;
ts.Commit(); // Required for add/modify to take effect

Handling Duplicate Names

try
{
    // Throws ArgumentException if style doesn't exist
    ObjectId styleId = doc.Styles.PointStyles["Name"];
}
catch (ArgumentException e)
{
    ed.WriteMessage(e.Message);
}

Document Locking (for Modeless Forms / Toolbox)

When code runs outside document context (modeless dialogs, .NET toolbox execution), explicitly lock the document:

using (DocumentLock locker = Application.DocumentManager
    .MdiActiveDocument.LockDocument())
{
    // Perform document/database modifications here
    CivilApplication.ActiveDocument.Settings
        .DrawingSettings.AmbientSettings.Station.Precision.Value = 2;
}

Settings Hierarchy

Settings apply at three levels (each can override the previous):

1. Drawing level - doc.Settings.DrawingSettings (units, zone, abbreviations, ambient settings)
2. Feature level - doc.Settings.GetSettings<SettingsAlignment>() (overrides drawing ambient for that feature)
3. Command level - doc.Settings.GetSettings<SettingsCmdCreateAlignmentLayout>() (overrides both)

// Feature settings
SettingsAlignment alignSettings = doc.Settings.GetSettings<SettingsAlignment>();
var angleSettings = alignSettings.Angle;
ed.WriteMessage("Precision: {0}, Unit: {1}\n",
    angleSettings.Precision.Value, angleSettings.Unit.Value);

// Command settings
SettingsCmdCreateAlignmentLayout cmdSettings =
    doc.Settings.GetSettings<SettingsCmdCreateAlignmentLayout>();
ed.WriteMessage("AlignmentType: {0}",
    cmdSettings.AlignmentTypeOption.AlignmentType.Value);

Note: Feature and command settings are in Autodesk.Civil.Settings — the same namespace as drawing/ambient settings. There is no separate Autodesk.Civil.Land.Settings namespace.

Property Value Pattern

In the .NET API, most properties use Property* classes implementing IProperty. Access values via .Value:

// COM: oComponent.Visibility = True
// .NET: oComponent.General.Visible.Value = true;

Error Handling Pattern

[CommandMethod("MYCOMMAND")]
public void MyCommand()
{
    Editor ed = Application.DocumentManager.MdiActiveDocument.Editor;
    try
    {
        using (Transaction ts = ...)
        {
            // work
            ts.Commit();
        }
    }
    catch (System.Exception e)
    {
        ed.WriteMessage("\nError: {0}\n", e.Message);
    }
}

Surface Namespace Conflict

Surface exists in both Autodesk.AutoCAD.DatabaseServices and Autodesk.Civil.DatabaseServices. Disambiguate with alias:

using CivSurface = Autodesk.Civil.DatabaseServices.Surface;

Gotchas

• Adding an element with a duplicate name throws an error - trap it
• Accessing a non-existent item throws ArgumentException
• Removing an in-use item throws an error
• ObjectIdCollection implements IList - can use foreach or index access
• Properties in .NET use .Value getter/setter (unlike COM's direct property access)
• Some properties have moved to sub-properties (e.g., Visibility -> General.Visible)

Related Skills

• c3d-project-setup - Project configuration and references
• c3d-label-styles - Label style creation and components
• c3d-pipe-networks - Gravity and pressure pipe networks (accessed via GetPipeNetworkIds / GetPressurePipeNetworkIds)
• c3d-sample-lines - Sample line groups and section views (accessed via alignment)