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IFC Export from Application Layers

This guide explains how Gemini maps geographic layers ("app layers") and attributes to IFC. You will learn how IFC entities, predefined types, and object types are used, how project/site is handled, and what you can expect from the current flat spatial structure.

Overview

What we export today

  • All selected objects are exported as IFC elements with geometry and IFC metadata.
  • We generate one IfcProject and one IfcSite, defined in the project settings.
  • All elements are placed directly under IfcSite (flat structure for now).
  • Spatial hierarchy (multiple levels, custom groupings, corridor hierarchies, and more) will come later.

IFC Attributes You Can Assign

Each object (feature) can have IFC-specific attributes. These determine what kind of IFC element it becomes.

You can add these attributes manually or use the Default_IFC.aly/gmi template in the sys folder.

IFC_ENTITY (required)

The IFC class that represents the object.

Some examples for infrastructure:

  • IfcSlab
  • IfcPipeSegment
  • IfcTerrain
  • IfcGeographicElement

IFC_PREDEFINEDTYPE (optional)

Used when the IFC class has type variants.

Examples:

  • IfcSlab: PAVEMENT, ROADWAY, WEG, USERDEFINED
  • IfcPipeSegment: CIRCULAR, RECTANGULAR, FLEXIBLESEGMENT, USERDEFINED

IFC_OBJECTTYPE (conditional)

Free text when:

  • PredefinedType = USERDEFINED, or
  • you need custom classification.

IFC_NAME and IFC_DESCRIPTION

Correspond to IfcRoot.Name and IfcRoot.Description.

Handling Infrastructure Geometry

Geometry in app layer Export as IFC Examples
Point Equipment/markers Signs, sensors, poles
Lines Linear elements Pipes, cables, track segments, guardrails
Polygons/surfaces Surfaces/slabs Roadways, embankments, slabs
TIN/3D solids Volume elements Concrete volumes, structural parts

Spatial Structure

Current solution (flat)

IfcProject
└── IfcSite
    ├── Element 1
    ├── Element 2
    └── ...

IFC Property Sets in App Layers

  • Can be assigned to the entire app layer (default for all objects).
  • Must currently be created manually as groups in the metadata.

Multiple Geometries per IFC Object

  • Imported as separate objects, but with the same S_PARENTGUID.
  • Export links geometries together based on S_PARENTGUID.

Export Flow

Procedure

  1. Set IfcProject and IfcSite in the project settings.
  2. Create app layers with the supported IFC attributes.
  3. Edit geometry and add attribute values.
  4. Export to IFC.
  5. Open the result in an IFC viewer.