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Enriching engineering design with a geospatial perspective comes with major advantages.

Geo-engineering and Geo-design require engineering and geospatial professionals to cooperate closely, bringing together data, technologies, and processes.

Information modelling, and Building Information Modelling (BIM) in particular, has become one of the key concepts in digital construction, particularly regarding engineering design visualization and validation, since it typically addresses key design data in the engineering space, focused on discipline / aggregated design for individual buildings.

Levering on both geospatial data and technology capabilities, Geo-enabled BIM thus unlocks new capabilities for Geo-engineering or Geo-design that go beyond individual buildings, and thus enables critical design considerations and validations across a larger area (Aggregated buildings across an area or Aggregated engineering discipline models in a large building)

Geo-BIM: key decisions to make

Traditionally, BIM is only used for the design and construction of individual buildings or constructions during the design and as-built stages of a project. It is seldomly used after the as-builting stage and only accessed by limited users. In other words, organizations are, today, not fully utilizing the potential of their BIM data.

GeoBIM can help organizations to make better use of their BIM data in business processes like emergency management, the identification of building code violations, the visualization or analysis of new building designs (including a holistic view on the surroundings), the integration with enterprise systems, etc. Apart from Geo-Enabling BIM for large buildings/constructions spread across large campuses, GeoBIM can be implemented at a large scale by organizations or agencies responsible for municipal or city administration and / or agencies administrating townships. Let us consider the 2 illustrative scenarios for decision making here below.

Scenario-1: The implementation of GeoBIM for all legacy buildings and constructions that city agencies manage today. Based on the importance of the buildings, the following legacy formats can be considered:
Option 1 – 2D CAD designs to BIM to GIS
Option 2 – Paper designs to BIM to GIS
Option 3 – Existing BIMs to GIS.

Scenario-2: The implementation of GeoBIM as part of the digitalization of the building permits process for new / proposed buildings, including the online submission and automated design validation.

With many agencies still managing their designs in 2D CAD drawings, another key question relates to whether to mandatorily enforce BIM submissions for all types of buildings and contractors, or whether to allow the smaller consultants and contractors(say managing small residential constructions) to still submit 2D CAD designs, and let the administrative agencies take responsibility to validate and/or convert the same to BIM using automated tools and templates.

Some of the COTS GIS technologies are enhancing GIS/BIM integration capability by providing functionalities to directly read BIM models. However migration of BIM models to GIS database is necessary for better utilization of BIM data like publishing over web or executing custom analytical tools across multiple models etc.,

What to convert to GIS

BIM holds a lot of engineering components and details, like structural, architectural, MEP, and Elevational, according to Level of details (LOD 100 – 500) represented in the model. It is therefore important to decide on which objects or features to migrate, especially in legacy data conversion or migration. An important driver in this decision naturally is the organizations’ vision and thought process related to the intended use of the Geo-BIM datasets.

For example, if an organization envisions to integrate BIM to Facility management or Asset management, the conversion and migration of all mechanical / electrical / plumbing components will be needed. On the other hand, if an agency, for example, wants to use GeoBIM for the validation of certain building codes, the creation of use of space statistics, general energy demand calculations, building visualizations, or emergency response management, it might be sufficient to migrate key architectural components and features.

Both options have their own advantages and return on investment.

Geo-BIM: Data modelling and technology considerations

The GeoBIM modelling approach does not require to migrate all engineering discipline BIM models to GIS with all features / information. Based on the migrated elements / objects and the level of details captured, the GIS data model can adopt the BIM Institute standard data model and customize it to GIS technology requirements for the relevant BIM objects identified to be migrated to GeoBIM.

Maintaining unique feature IDs helps in integrating GeoBIM objects to external databases or in establishing feature relationships. In addition, maintaining floor relationships while migrating is important for locating, analytical purposes, bill of quantities etc.

Modelling complex elements, like stairs and railings, in a GIS system is more complex compared to BIM systems, as BIM technologies maintain these objects as complex/grouped elements. To address this challenge, and facilitate GIS databases to treat these complex elements as one, custom data models, relevant 3D GIS objects like multi-patch geometry, feature ID relationships must be used. In addition,

customized ETL tools need to be built to migrate such complex elements from the native BIM formats to the customized GIS models.

A carefully considered approach to identify the required attribute datasets, that will enable spatial analysis or integration with asset management
applications, is required when establishing the GIS for MEP elements. For a pipe, for example, the following attributes can be considered:

• • Flow stream
  • Diameter
  • Area (cross section)
  • Material
  • Length
  • Insulation
  • Lining
  • Air flow properties like

– Status
– Pressure
– Flow rate
– Flow velocity
– Pressure drop

Integrated GeoBIM and 3D city model: As you may have read in Avineon ’s article on “GeoBIM: Data Formats & models for converging 3D GIS &BIM” Read more
city GML objects/buildings with real texturing can be migrated to a GIS database and published as map/scene services using GIS server technologies. 3D city layers can be overlaid on GeoBIM layers and custom applications, like roof Solar potential calculations, can be developed.

The integrated data model for BIM and 3D city models uses CityGML and 3D Vector Scene objects in GIS and can enable a high-quality visualization of textured building overlays on top of Geo-BIM models.

Geo-BIM: Conversion approach

Legacy designs: CAD, Paper, BIM format

Avineon typically adopts the GeoBIM approach illustrated in figure 1. We have identified the constraints / limitations in various COTS technologies and augmented our approach with custom tools to achieve an efficient and automated CAD->BIM->GIS conversion without any data loss while maintaining data/feature integrity.

Standardizing CAD design templates is key to an efficient GeoBIM conversion process that continues to allow CAD design submissions from contractors. To enable an automated conversion, CAD templates must address attribute and BIM capture requirements, like object library (families) definition, and unique geometry capture requirements.

BIM / GIS conversion tools/technologies

Various COTS ETL tools convert BIM models to GIS with a certain level of completeness and accuracy. Open formats, like IFC, can be used to convert BIM models to GIS. However, there are constraints/short comings in terms of loss of attribute data, slow performance in data loading/reloading, publishing etc.,
We have observed that, when loading large numbers of BIM models (say a few thousands) in case of city-wide Geo BIM databases, COTS software has limitations in managing complex elements in terms of performance/speed using front end loading tools. This becomes a challenge when there is a need to load BIM models multiple times or load changes to the GeoBIM models.

As illustrated in figure 2, Avineon has derived a unique hybrid approach by utilizing COTS tools for their strengths and by developing both custom ETL tools, to load complex elements to datastores through backend procedures, and procedures to load changes / deltas separately, ultimately providing flexibility, a higher speed and lesser downtime.

Avineon also developed/adopted custom tools to load complex elements, like stairs/ramps/railings, and attributes that got lost during COTS ETL based migration, while maintaining GIS data model integrity requirements.

GeoBIM: Web enabling

Publishing geospatially located 3D models or datasets over web is an effective way to communicate designs to a wider audience, as design options can be evaluated easily by using switchable level structures. This is one of the key purposes of GeoBIM.

GeoBIM provides an opportunity to overlay all the underground utilities and terrain data available in GIS as web services with a new building model. The integrity of this data is critical to ensure no interferences occur during construction.

Client/Server based GIS technologies provide dynamic and flexible data sharing/visualization/ analysis/ hosting/access options, avoiding license overheads and software installation overheads.

Powerful APIs of GIS technologies empower decision makers with ample opportunities to develop custom tools to address various user needs and integration needs.

Ex. GIS technology APIs provide an opportunity to develop geolocation-based network tracing in the 3D space and identification and visualization tools for facility management and maintenance.

Specialized tools like Virtual Reality views, Heating / Cooling demand, Solar potential calculation, Material dashboards, Volume vs Footprint, Building code validations, Shadow analysis etc., can be developed using Geo-BIM models and aggregated over spatial regions like administrative boundaries.

Figure 3: GeoBIM integrated with 3D city model providing BOQ for a selected building over web

Figure 4: GeoBIM integrated with 3D city model providing solar potential for a roof over web

• Avineon has developed and implemented an end-to-end GeoBIM strategy for converting a large volume of legacy buildings for a municipal authority and brings proven and referenceable experience to its customers who aspire to develop a GeoBIM strategy to meet their business goals.
• Avineon has developed an efficient and automated approach for converting and migrating legacy CAD designs to GeoBIM databases and publish over web, with all the web portal functionalities to view, query, analyze and maintain the database and to successfully deploy the datastores in a LIVE environment. Avineon’s web-based GeoBIM viewer and custom-built value-added tools can quickly provide the targeted business value that clients aim to achieve from their GeoBIM strategy.
• Avineon also provides consultancy services to define and establish BIM standards, CAD standards, and data capture specifications, which are key for developing a successful ecosystem between suppliers, contractors, and end-users to seamlessly create and maintain GeoBIM databases and meet the organizational business and functional requirements.

Over the last few years, we have witnessed a significant transformation in the AEC (Architectural, Engineering and Construction) industry.

Over the last few years, we have witnessed a significant transformation in the AEC (Architectural, Engineering and Construction) industry. The interrelationships between building information modeling (BIM) on the one hand, and geospatial, or geographic information system (GIS), technologies on the other hand, have been gradually increasing. By integrating GIS and BIM, planners can generate digital twins to visualize projects from any perspective, improving stakeholder communication and participation. Thanks to this digital twin representation, stakeholders can easily see what the project will look like in “real life” – not only taking into account the terrain, but also the surrounding infrastructures (including underground infrastructures), and the overall general environment in which the project will reside Read more

Collating inputs from various disciplines makes the models even more realistic, enabling better solutions for planning and designing that allow the construction, operation and maintenance of large-scale geographically spread infrastructure in a sustainable manner. In addition, costs decrease because costly, and time-consuming, errors are avoided.

However, to fully exploit and reap all the benefits of GeoBIM, it is important to understand the related Geospatial (GIS) and BIM concepts. Here we briefly explain the concepts behind 3D GIS and BIM, based on open standards and vendor neutral technologies.

CityGML and IFC

In most cases, two standardized data formats, from the two most prominent semantic 3D modelling formats for buildings, are used in the AEC industry: (i) City Geography Markup Language (CityGML), used in the field of 3D GIS, and (ii) Industry Foundation Classes (IFC), an open data model for Building Information Modeling (BIM).

In 3D GIS, CityGML is an open standardized data model and exchange format to store digital 3D models of cities and landscapes. It is published by the Open Geospatial Consortium (OGC, https://www.ogc.org/standards/citygml) and defines ways to describe most of the common 3D features and objects present in cities, such as buildings, roads, rivers, bridges, vegetation and city furniture, and the relationships between them. It also defines different standard levels of detail (LoDs) for the 3D objects, which allow the depiction of objects for different applications and purposes, such as simulations, urban data mining, facility management, and thematic inquiries.

In BIM, the Industry Foundation Classes (IFC, https://www.buildingsmart.org/standards/bsi-standards/industry-foundation-classes/) data model is a neutral and open specification that is not controlled by a single vendor or group of vendors. It is an object oriented file format, with a data model developed by buildingSMART, to facilitate interoperability in the AEC industry. It is a commonly used format for collaboration in projects related to Building Information Modeling (BIM). IFC models everything – from the individual components up to building. CityGML, on the other hand, defines five Levels-of-Detail (LoDs) for building models, where each level then describes what geometric and semantic representations are expected.

1. Concept of Level of Detail (LoD) in CityGML

Level of Detail (LoD) is an important concept in 3D city modelling that defines the degree of abstraction of real-world objects. It is primarily designed to optimize the amount of details of real-world objects by considering specific user needs, computational elements, and economical aspects. CityGML provides a standard model and mechanism for describing 3D objects with respect to their geometry, topology, semantics, and appearance. Based on these parameters, it defines five different levels of detail as illustrated in Figure 1.

Figure 1: The five LODs of CityGML 2.0.

Description of LODs in City GML version 2.0

Both the geometric detail and the semantic complexity increase from LOD0 up to LOD4, that contains indoor features.
In all LoDs, it is possible to map textures onto the structures.

Table 1: Level of Detail

2.Concept of Level-of-Development (LOD) in BIM

In IFC, the Level of Development (LOD) framework is used to specify how much a BIM element has developed. They are helpful for communication and coordination since they can be used to indicate stages or milestones.

The acronym Level-Of-Development (LOD) (capital ‘o’) in BIM, that indicates the state of development from conceptual (LOD 100) to as-built (LOD 500), is therefore not to be confused with Level-of-Detail in CityGML. As mentioned before, LoD in City GML defines the degree of abstraction of real-world objects.

Figure 2: Level of Development in BIM

As the LOD increases, the level of detail and the information contained in BIM elements increase as well. The features of building components at each LOD stage are listed below.

Table 2: Level of Development

3.Differences between City GML and IFC data

Despite apparent similarities between CityGML and IFC formats at a high level, there are major differences between the two. The conversion to CityGML involves both geometric calculations and the mapping of semantics. While IFC models are built using mostly primitives and swept solids in combination with Constructive Solid Geometry (CSG), CityGML only uses Boundary-representation, as illustrated in Figure3
B-rep, CSG and Sweep volumes

Figure 3: The three possible approaches for representing 3D objects in IFC

• B-rep – B-rep represents a solid body by planar faces that are located at the boundary of the body and completely enclose the body. Each face acts as the border between what is inside and outside the body.
• CSG – CSG is used to create solid bodies by one or many Boolean operations on base solids. A Boolean operation between two geometries generates a new geometry which can, for example, be the union, difference or intersection, as illustrated in Figure 4

Figure 4: Boolean operations between a cube and a sphere

• Sweep volumes – Sweep volumes define a solid body by a 2D profile and a path. The geometry of the body is computed by moving the profile along the path. The 2D profile can be a primitive shape, such as a disk or a polygon, and the sweep can either be a linear extrusion or a rotational sweep, where the path is defined by an axis and an angle.

The geometry of the latter two types are stored implicitly, meaning that the geometry is generated by calculating parameters. An IFC viewer/reader must apply the sweeping and CSG computations before being able to visualize or use the objects. Figure 5 illustrates an example of this for implicit CSG geometry. The figure also depicts how, at the same time, the relations between a door and a wall are stored.

Figure 5: An example of implicit geometry: the wall is cut by the opening element using the Boolean difference. The door is then placed within the gap in the wall

Calculating the explicit B-rep geometry does not yield a unique solution. For e.g., a disk should be converted to a regular polygon, but the number of sides of the polygon depends on the converter. For the purpose of creating valid CityGML geometries, it is sufficient to have the geometry correctly representing the original model. Although there are three geometric models, in practice, most IFC models are built using sweep volumes and CSG.

One difference between IFC and CityGML is that in IFC, implicit geometry refers to the geometry that is implied by the parameters stored in the IFC file and the definitions in the IFC Object Model specification. In contrast, according to the CityGML standard, implicit geometry is geometry that is stored once, as a template, and can then be reused multiple times by referring to it.

Conclusion

To successfully integrate GIS and BIM, and thus fully reap the benefits of GeoBIM, a good understanding of the related GIS concepts on the one hand, and the related BIM concepts on the other hand is key. Thanks to our experience, knowledge, and expertise in the domain of GeoBIM, Avineon has built this understanding. We help your project planners, designers, and developers generate the digital twin that they need to visualize their projects in the real world, allowing your organization to experience the benefits of more sustainable and cost-effective project planning and execution.

For more information on our product & services, contact us: gssbd@avineonindia.com

Geographic Information System has been traditionally used to model the urban infrastructure and perform 2D spatial

Geographic Information Systems have been traditionally used to model the urban infrastructure and to perform 2D spatial analysis on databases covering large areas in less detail. With advancements in technology, and improved data acquisition methods, GIS models have become more detailed, covering 3D information of individual buildings – traditionally, the domain of Building Information Modelling (BIM).
	On the other hand, the BIM domain focuses more on semantically rich information about the design, materials, construction, and other physical elements of building sites. Over the years, BIM has also moved to the mainstream, scoring over traditional building design platforms based on 2D CAD drawings. Further, as BIM users felt the need to incorporate the surrounding features into their design workflow, the BIM domain is continuously enhancing its standards to support this type of information, that exists in GIS datasets. Consequently, GIS and BIM are now integrating by modelling the same objects. Despite having a convergence, GIS and BIM domains retain their own focus and characteristics for modelling urban infrastructure elements, and hence the data is represented and stored at varying levels of detail or abstraction in each system.
With the goal of deriving the best of both worlds, this convergence has triggered technology advancements to integrate Geo-information and BIM. In the urban context, the integration of GIS and BIM results in highly comprehensive 3D city models and Digital Twins of various city components. In addition, the integration of GIS and BIM data helps to avoid redundant modelling and facilitates data flows in both directions across software applications.