Lecture 5

Lecture Overview

• Subject: Considerations of BIM and GIS Integration

• Course: LSGI3220: Building Information Modelling & 3D GIS

• Institution: Department of Land Surveying & Geo-Informatics, The Hong Kong Polytechnic University

Review Questions from Previous Lectures

• Definition, purpose, and latest version of CityGML

• General characteristics of CityGML

• Identification of two types of modules in CityGML and the core module count

• Understanding the five Levels of Detail (LODs) in CityGML

• LOD regarding architectural models of windows and doors

• Purpose of code lists in CityGML

• Basis for integrating CityGML and IFC

CityGML Summary

• Definition: CityGML outlines ways to depict physical and semantic properties of city elements such as buildings, roads, rivers, and vegetation.

Strengths of CityGML

• Functions as a data exchange format for 3D GIS

• Considered a BIM-lite data model

• Open standard with cross-industry adoption

• Object-oriented model with distinct LODs

• Supports semantic models for thematic queries and data mining

• Useful for facilities management and contributes to digital twin applications

Limitations of CityGML

• Poor scalability due to focus on XML without spatial indexing

• Complex data model requiring specialized tools like FME

• Not tailored for client-oriented formats; requires conversions for mobile/web tools

• Insufficient for comprehensive BIM needs; mainly focused on community and city scales

CityGML Structure

• Organizes various modules:

  • Vegetation, WaterBody, CityFurniture, Relief, Tunnel, Building, Bridge, and Transportation modules.

• Hierarchical representation within modules:

  • Building module contains components like BuildingPart, Roof, Windows, Doors, Walls, etc.

CityGML and Digital Twin Concepts

• Definition: Digital Twin is a real-time digital counterpart of a physical object/process.

• Emphasizes that CityGML models not only 3D geometry but also real-world object details.

• CityGML offers semantic richness, allowing for modeling of nuanced features like wall materials and city furniture components.

BIM and 3D GIS Integration Considerations

• Comparison of IFC and CityGML:

  • GIS (CityGML): Focuses on geographic information, existing data, and city-wide perspectives.

  • BIM (IFC): Focuses on building information, typically modeling new structures at building scales.

Key Integration Aspects

1. Scales: Relationship of planned buildings to larger regional contexts.

2. Geo-referencing: Different coordinate systems for precise locations.

3. Modeling Paradigms: Distinct approaches in Building and Geoinformatics sectors.

4. Geometry Representation: Differences in geometric representations between BIM (parametric and volumetric) and GIS (boundary representation).

5. Standards: Importance of standards in facilitating data sharing and usage across domains.

Geo-referencing Techniques

• BIM: Bottom-up approach from idea to real-world objectives.

• GIS: Top-down approach focusing on surveying and modeling existing structures.

• Emphasis on local (PCS) versus global (CRS) coordinate systems.

Levels of Detail (LOD)

• LOD determined to manage large-scale GIS data:

  • LOD 0: Regional Models

  • LOD 1: City/Site Models (Block Models; no roofs)

  • LOD 2: City/Site Models (Textured, differentiable roofs)

  • LOD 3: Detailed architectural models

  • LOD 4: Interior walkable architectural models

Standards Overview

• Importance of standards for interoperable data use across various domains and software:

  • Key Organizations: BuildingSMART (IFC), Open Geospatial Consortium (CityGML), ISO standards relevant to geographical and building data.

• Comparisons between GIS and BIM models regarding geometry, semantics, detail levels, etc.

Conversion Between IFC and CityGML

• Examines methodologies to convert IFC objects to CityGML models:

  • Use of Triple Graph Grammar to maintain semantic and geometric compatibility.

  • Need for Application Domain Extensions (ADE) to preserve additional relevant information.

  • Focus on detailed conversion practices that enhance usability without sacrificing essential data.

Example Showcases of Conversion Process

• Near-lossless conversion discussed in relation to Singapore's 3D city modeling projects, utilizing methodologies to address complexities in preserving data integrity during conversion from BIM to CityGML.

Conclusion and Q/A

• Reminder about mid-term test details.

• Open floor for questions and clarifications regarding the lecture content.