> ## Documentation Index
> Fetch the complete documentation index at: https://docs.speckle.systems/llms.txt
> Use this file to discover all available pages before exploring further.

# Civil 3D Schema

> Data schema and structure for Civil 3D models

The Civil 3D connector exports civil engineering entities from Autodesk Civil 3D, preserving layer organization and property set data.

## Hierarchy

Civil 3D models are organized by File and Layer:

```mermaid theme={null}
graph TD
    A[Root Collection] --> B[Civil 3D File]
    A --> C[Proxies: RenderMaterial array]
    A --> D[Proxies: Color array]
    A --> E[Proxies: Group array]
    A --> F[Proxies: Definition array]
    A --> G[Proxies: PropertySetDefinition array]
    
    B --> H[Layer]
    H --> I[Civil3dObject]
    H --> J[Geometry<br/>standalone]
    H --> K[Instance]
```

The hierarchy reflects Civil 3D's layer structure:

* **File** - The Civil 3D file
* **Layer** - AutoCAD layer (Civil 3D entities are organized by layer)

## Object Types

Civil 3D exports three types of objects:

1. **Civil3dObject** - Civil 3D entities (alignments, surfaces, pipes, etc.)
2. **Geometry** - Standalone geometry objects
3. **Instance** - Block references pointing to Definition proxies

## Civil3dObject Structure

Civil3dObject extends [DataObject](/developers/data-schema/object-schema) with these additional fields:

```json theme={null}
{
  "id": "string",
  "speckle_type": "Objects.Data.DataObject:Objects.Data.Civil3dObject",
  "applicationId": "string",
  "name": "string",
  "properties": {
    "string": "any value"
  },
  "displayValue": [
    "Base (geometry objects)"
  ],
  "units": "string",
  
  "__comment": "Civil3dObject-specific fields",
  "baseCurves": [
    "ICurve (geometry objects)"
  ]
}
```

### Connector-Specific Fields

* **`baseCurves`** - An array of curve geometry objects representing the base curves of the Civil 3D entity (e.g., alignment centerline, pipe centerline)

## Properties

Civil3dObject `properties` contain:

* **Extension Dictionaries** - Custom data stored in extension dictionaries
* **XData** - Extended entity data
* **Property Sets** - Civil 3D property set definitions
* **Part Data** - Entity-specific part data
* **Additional class properties** - Properties that depend on the entity type (alignment, surface, pipe, etc.)

```json theme={null}
{
  "properties": {
    "Extension Dictionaries": {
      "CustomApp": {
        "Key": "Value"
      }
    },
    "Property Sets": {
      "Pipe Properties": {
        "Diameter": 0.3,
        "Material": "PVC"
      }
    },
    "Part Data": {
      "Part Family": "Pipe",
      "Part Size": "300mm"
    }
  }
}
```

## Proxies

Civil 3D models use these proxy types:

### RenderMaterial

Material assignments for visual representation.

### Color

Color assignments for objects.

### Group

Group proxies encode group memberships.

### Definition

Definition proxies store geometry for block definitions.

### PropertySetDefinition

Property set definition proxies encode Civil 3D property set definitions. These define the structure for property sets used by Civil3dObjects.

## Example: Civil3dObject

```json theme={null}
{
  "id": "civil3d-abc123...",
  "speckle_type": "Objects.Data.DataObject:Objects.Data.Civil3dObject",
  "applicationId": "entity-456",
  "name": "Alignment - Main Road",
  "properties": {
    "Property Sets": {
      "Alignment Properties": {
        "Length": 1250.5,
        "Start Station": 0.0,
        "End Station": 1250.5
      }
    },
    "Part Data": {
      "Entity Type": "Alignment",
      "Style": "Centerline"
    }
  },
  "displayValue": [
    {
      "speckle_type": "Objects.Geometry.Polyline",
      "points": [
        {"x": 0, "y": 0, "z": 0},
        {"x": 100, "y": 50, "z": 0},
        {"x": 200, "y": 100, "z": 0}
      ],
      "units": "meters"
    }
  ],
  "baseCurves": [
    {
      "speckle_type": "Objects.Geometry.Polyline",
      "points": [
        {"x": 0, "y": 0, "z": 0},
        {"x": 100, "y": 50, "z": 0},
        {"x": 200, "y": 100, "z": 0}
      ],
      "units": "meters"
    }
  ],
  "units": "meters"
}
```

## Invariants and Caveats

1. **baseCurves field** - Civil3dObjects have a `baseCurves` array in addition to `displayValue`
2. **Property Sets** - Civil 3D property sets are stored in `properties.Property Sets`
3. **Entity-specific properties** - Properties vary by entity type (alignment, surface, pipe, etc.)
4. **Layer organization** - Objects are organized by AutoCAD layer structure
5. **PropertySetDefinition proxies** - Unique to Civil 3D, these define property set structures

<Accordion title="What's the difference between baseCurves and displayValue?">
  * **baseCurves**: The fundamental curve geometry of the entity (e.g., alignment centerline, pipe centerline)
  * **displayValue**: The visual representation (may include additional geometry like labels, annotations, or meshed surfaces)

  For some entities, `baseCurves` and `displayValue` may contain similar geometry, but `displayValue` is optimized for visualization.
</Accordion>

## Related Documentation

* [Object Schema](/developers/data-schema/object-schema) - Base object structure
* [Geometry Schema](/developers/data-schema/geometry-schema) - Geometry storage
* [Proxy Schema](/developers/data-schema/proxy-schema) - How proxies work