Parcel.md

Parcel Class

Overview

Parcel represents a 2D closed area in Civil 3D, typically representing a plot of land or a right-of-way. Parcels are dynamic topological entities; they are automatically formed and updated by the geometry (Parcel Segments or Alignments) within their parent Site.

Namespace

Autodesk.Civil.DatabaseServices

Inheritance Hierarchy

System.Object
  └─ RXObject
      └─ DBObject
          └─ Entity
              └─ Feature
                  └─ Parcel

Key Properties

Property	Type	Description
Area	double	Area of the parcel.
Perimeter	double	Total perimeter.
Name	string	Parcel name/number.
Number	int	Automatic parcel number.
SiteId	ObjectId	The site it belongs to.
UserDefinedProperties	UDP	Custom property bucket.

Key Methods

Method	Return Type	Description
Create(...)	ObjectId	Static methods to create from objects.
CreateFromObjects(...)	ObjectId	Creates parcels from CAD polylines.

Code Examples

Example 1: Creating Parcels from Polylines

using (Transaction tr = db.TransactionManager.StartTransaction())
{
    ObjectId siteId = ...; // Get target Site
    ObjectIdCollection polyIds = ...; // Polylines to convert
    
    ObjectIdCollection createdParcels = Parcel.CreateFromObjects(
        polyIds, 
        siteId, 
        db.CurrentSpaceId, 
        false // Erase existing entities?
    );
    
    ed.WriteMessage($"\nCreated {createdParcels.Count} parcels.");
    tr.Commit();
}

Example 2: Reading Parcel Area

Parcel p = tr.GetObject(id, OpenMode.ForRead) as Parcel;
ed.WriteMessage($"\nParcel {p.Name}: Area = {p.Area:F2} sq ft");

Example 3: Renumbering Parcels

// Renumbering is usually a Site-level operation or done via properties
p.Name = "Lot " + p.Number;

Example 4: Getting Segment Geometry

// Parcels don't own the geometry directly; they are defined BY segments.
// To get the shape, you might look at the base curves.

Example 5: Working with UDP (User Defined Properties)

// Civil 3D allows custom fields on Parcels (e.g., "Zoning", "Owner")
// Accessing these requires the UDP API (UserDefinedPropertyClassification)
// This is advanced and involves `Parcel.GetUserDefinedPropertyValue`.

Example 6: Topological Updates

// If you draw an Alignment through this Parcel (in the same Site),
// The Parcel will split into two AUTOMATICALLY.
// The API reflects this: the original Parcel object usually shrinks,
// and a new Parcel object is created for the split piece.

Example 7: Inverse/Map Check

// Getting the "Legal Description" geometry
// Iterate segments...

Example 8: Styles

p.StyleId = newStyleId; // Change visual style (e.g., "Single-Family")
p.AreaLabelStyleId = newLabelStyleId; // Change label style

Best Practices

1. Topology Awareness: Remember that modifying ONE segment can affect TWO parcels (shared edge).
2. Site Management: Ensure you are working in the correct Site. Parcels cannot exist without a Site.
3. Automatic Updates: Because Parcels react to other geometry, GUIDs/IDs are stable, but geometry is volatile.

Related Objects

• Site - The container.
• Alignment - Can form parcel boundaries.

References

• Autodesk Parcel Reference