01: Existing Conditions Modelling

Existing Conditions Modelling is a process of creating a 3D model of the existing site conditions, such as 3D point cloud model, 3D mesh model and 3D individual photo-realistic models. The existing conditions model should be developed by land surveyor from laser scanning, photogrammetry, conventional survey method, record drawings and digital map products available from Lands Department. For historic graded buildings, the author shall include heritage documentation and assessment prepared by the architect and structural engineer. The existing condition models are used for design visualisation and planning, as well as field verification and facility management. They shall be supplemented by photographic records.​ In the planning / design stage, the existing site condition, and existing building condition for alterations and additions (A&A), shall be surveyed by the above-mentioned technologies to produce 3D point cloud and / or mesh model to facilitate project planning and design development. If necessary, 3D individual photo-realistic models or Information Models of existing structure / building can also be generated.​In the construction stage, 3D digital survey technology such as laser scanning shall be employed to provide verification of the as-built condition for the construction works. It also provides documentation of the environment for future modelling, design coordination and facility management.

Description

A process in which a project team develops a 3D model of the existing conditions for a site, facilities on a site, or a specific area within a facility. This model can be developed in multiple ways including laser scanning, photogrammetry and/or conventional surveying techniques, depending on what is desired and what is most efficient. Once the model is constructed, it can be queried for information, whether it is for new construction or a modernization project.

Potential Value

• Enhance the efficiency and accuracy of existing conditions documentation

• Provide documentation of environment for future uses

• Aid in future modeling and 3D design coordination

• Provide an accurate representation of work that has been put into place

• Verify project status with quantity information for progress monitoring

• Provide detailed layout information

• Pre-disaster and post-disaster planning and documentation

• Visualize current and future facility status and plans

Resources Required

• Building Information Model authoring software

• Laser scanning point cloud manipulation software

• 3D Laser scanning

• Conventional surveying equipment

Team Competencies Required

• Ability to manipulate, navigate, and review a 3D model

• Knowledge of Building Information Model authoring tools

• Knowledge of 3D laser scanning tools

• Knowledge of conventional surveying tools and equipment

• Ability to sift through mass quantities of data that is generated by a 3D laser scan

• Ability to determine what level of detail will be required to add “value” to the project

• Ability to generate Building Information Model from 3D laser scan and/or conventional survey data

References for Additional Information

United States General Services Administration (2009). “GSA Building Information Modeling Guide Series: 03 - GSA BIM Guide of 3D Imaging.” [link] Arayici, Y. (2008). “Towards building information modeling for existing structures.” Structural Survey 26.3: 210. ABI/INFORM Global. [link] Murphy, M., McGovern, E., and Pavia, S. (2009).”Historic building information modelling (HBIM).” Structural Survey 27.4: 311. ABI/INFORM Global. Adan, A., Akinci, B., Huber, D., Pingbo, Okorn, B., Tang, P. and Xiong, X. (2010).“Using Laser Scanners for Modeling and Analysis in Architecture, Engineering, and Construction.”

Potential Output Information

• 3D point cloud of existing building

• Surface model of existing geometric elements

• Parametric model including data regarding existing building components

Source: BIM Project Execution Planning Guide, Ver. 2.2 with minor revisions.