Building information has been collected and maintained on regional and national level for centuries. During the last decades 3D representations of buildings have become increasingly common, especially in larger cities, as parts of 3D city models. Already in 2012 there were more than a thousand city models worldwide [1
] and the number is growing [2
]. Reasons for creating 3D city models vary, earlier the models were mainly used for visualization, but now they are used for other purposes as well, such as urban planning, decision making, analyses, and also to replace the 2D base maps in urban areas, which requires that the city models have connections to e.g., cadastral registers. To support these new requirements on the 3D city models, there is a need for new national standards to obtain a more uniform management of the building information. Some countries have recognized this need and have created national 3D building or city model standards, for example the Netherlands [4
] and Germany [5
3D representations of buildings are also common in architecture, engineering, and construction (AEC) companies where 3D computer aided design (CAD) models are now often replaced by more advanced building information models (BIM). Earlier 3D building representations were mainly used for presentation, but there is an increasing interest in using BIM for analyses and integration with geodata in 3D city models. Such 3D city models play an important role in the digital transformation of the built environment process and requires, among others, that there is a linkage between city models and BIM. This sets new demands on the models, but it also allows for new categories of people and applications to use them. Depending on the purpose of a 3D city model and expertise, the models are developed on different platforms using different techniques, e.g. using 3D GIS, BIM, or computer graphics [2
One obstacle with linking building information between BIM and 3D city models is that 3D city models generally have a hierarchically strict structure as opposed to BIM where the same information can be described and associated in many ways [7
]. One possible way to overcome such interoperable issues is to use a classification system. National classification systems have been used for a long time in the AEC industry, but their linkage to 3D city model applications have not been well studied. Other advantages of using a classification system in the BIM to 3D city model transformation is that the classification will enable common definition of terms, it can specify which elements to be included in BIM, and it will facilitate an automated conversion [10
There is a need to complement a building or 3D city model standard with measuring guidelines to ensure that city objects are created in a uniform way, regardless of whether the geometric part of the building information is created from laser scanned or photogrammetric data, which is still most common, or from BIM. Examples of issues that can affect the resulting model are, among others, the minimum sizes of objects to include, how objects are measured (e.g., using mean roof height for roof measurements) [12
], and the way the building objects are described (e.g., restricting which geometry types that are allowed) [13
There are several aspects to consider in creating a national building standard. First the application requirements should be specified. Second, an international standard to conform to should, if possible, be chosen. The reason for this is that an international standard is often well established and is likely to be implemented by more software tools. Third, a classification system should, if such a system exists, be included in the standard to improve definition of terms and facilitate interoperability with several urban processes. Finally, the standard should be complemented with measuring guidelines to ensure a more uniform creation of the building objects.
The aim of this paper is to present a proposal for a national building standard in Sweden. In the study we (1) specify requirements for building objects, (2) develop a standard based on the requirements, (3) create test data according to the standard and perform some case studies, and (4) evaluate the proposed standard. It should be noted that the situation in Sweden resembles many other countries which make the results of the study general.
The paper is organized as follows. Section 2
gives an overview of applications for building information in 3D city models and BIM. Section 3
provides an overview of standards for the built environment, with the intention to both describe the standard to which the proposed Swedish standard should conform, and to other standards to which it could relate. Section 4
describes related work in this field. Section 5
describes requirements on building information at a national context. In Section 6
the development of a Swedish building standard is described and Section 7
evaluates the standard and describes test cases against the requirements. In Section 8
the findings are discussed and finally Section 9
concludes the paper.
2. Applications of 3D City Models and BIM
There are several applications for 3D city models, in [2
] the authors identified 29 different types of use cases, for example energy demand estimation, building type classification, propagation of noise, 3D cadaster, urban planning, emergency response, and facility management. The diversity of use cases shows that 3D city models can be used for many purposes and this should be considered when planning for the implementation of a new 3D city model.
The integration of BIM and 3D city models can increase the use of the 3D information. The authors of [6
] describe applications where combined BIM and 3D geodata city models are used, for example: 3D cadaster, where BIM contributes with more detailed geometry information and geodata with information about ownership and transaction history; navigation, where BIM provides indoor and geodata outdoor information; and urban environment analysis, where analyses of e.g., indoor climate, sunlight visualization, and energy consumption require both BIM and geodata.
] the authors analyzed the functionality and usability of 19 3D city models in six Finnish cities. The following criteria were used: platform used; data accessibility, regional data coverage, and the use of as-planned information (e.g., BIM). 3D modelling experts were interviewed and the possibility to find real-time information, to interact, and better include stakeholders in the decision-making processes were described as important benefits. 3D city models should also include lifecycle management to support different decision-making processes in the municipalities. Most of the studied 3D city models included a small geographic area and had limited functionalities, but this was not what the cities had expected. In [3
] the authors grouped the studied projects into three 3D city model categories: 3D GIS, BIM, and computer graphics. The categories overlap, but no project belonged to all categories. To capture all characteristics, a 3D city model should include all three perspectives and to accomplish this, a concept for harmonizing 3D city modelling is proposed (Figure 1
A drawback with a comprehensive 3D city model is that it includes many different user perspectives which can result in a very complex model. For many use cases a simple model will suffice, and a complex model with unnecessary information could cause problems. The research presented in [14
] is critical to 3D city models that are too comprehensive for their purpose. To overcome this Kang describes five BIM-GIS integration levels (BG-IL) where the simplest integration is a coordinate reference system integration (BG-IL1), followed by geometry model integration (BG-IL2), element data integration (BG-IL3), relationship integration (BG-IL4), and finally the most advanced integration, semantic information integration (BG-IL5). Use cases can be mapped to the integration levels, for example visualization would require BG-IL2, facility management BG-IL3, navigation services BG-IL4, and semantic information queries BG-IL5.
5. Requirements for the National Building Standard
National standards for 3D buildings and city models demand a requirement analysis [3
]. Will the 3D building data only be used for visualization or should it also be used for analyses? Both cases can affect the complexity of the model, but in different ways. For cartographic visualization, the building information may need to be generalized to improve performance. In the latter case, the analyses to be supported could affect the complexity of the model. That is, what additional textual, semantic, and geometric information should be included in the standard to fulfil all the specified requirements. One way to assure that the potential usage of the building information is reached is to create implementation requirements that, as far as possible, are measurable (see [4
]). This can be used to verify to what extent the requirements are fulfilled once the standard has been implemented.
There is currently no well adopted national standard for 3D buildings in Sweden. The Swedish 2D and 3D building specification [36
] was finalized in 2018, but it has not been implemented in production, and new requirements have emerged, such as better support for the planning and building process. To investigate the requirements as well as test and evaluate the standard a national project was launched. The project was coordinated by Lantmäteriet (the Swedish mapping, cadastral, and land registration authority); the project also included experts from academia, some larger cities and technical consultants (see [47
]). The results from the project are reported to Geodatarådet, a board that governs the development and use of new geodata standards in Sweden. The proposed national building standard has the working name CityGML Sve-Test.
The standard does not need to support other domain-specific applications, such as noise or energy flow modelling. However, it should be possible to extend the building standard to support these applications. Furthermore, it should be possible to complement the building standard with information or standards of other themes to create a comprehensive national 3D city model standard.
Based on the description above, the requirements used in the development of a proposal for the new Swedish national building standard, CityGML Sve-Test, are:
The national building standard should support the representation of both 2D and 3D buildings.
In order to be interoperable with city models, to be able to view the building information in software and use common tools for data conversion from e.g., BIM (IFC), the national building standard should comply to an official international standard that is well established and implemented by other countries or cities.
The national building standard should be supplemented with surveying and modelling guidelines to ensure a uniform implementation (e.g., similar to [44
] and [13
The national building standard should include all attribute information from the Swedish specification for 2D and 3D buildings [36
The Swedish construction classification system CoClass [38
] should be used in the national building standard. CoClass is also recommended to be used in BIM-models and using CoClass in both BIM and geodata models will facilitate integration and conversion between these data domains.
All references from the national building standard to registers, 2D models etc., should be performed using external referencing.
From a cadaster perspective the national building standard should support:
visualization of a simplified 3D cadaster;
link to the BIM where the borders of the 3D cadaster are defined using external referencing;
link to 2D cadaster, 3D cadaster, and other relevant cadastral information using external referencing.
The national building standard should support the building permit process with:
additional information and links to other registers that is required for the building permit process using external referencing;
conversion of a (standardized) BIM model to enable visual as well as quantitative rule checking of building permit rules (in e.g., a digital detail development plan).
7. Evaluation of CityGML Sve-Test
7.1. Evaluation Methodology
7.2. Conformance to the National Implementation Requirements
The first implementation requirement states that an official international standard should be used. CityGML Sve-Test is a CityGML 3.0 ADE, and even though this is a proposed new version of the standard, it can be assumed that this version will be as well established as CityGML 2.0 in the future. The national 3D city model standard should be supplemented by surveying and measuring guidelines, and if CityGML Sve-Test becomes the official building standard in Sweden, corresponding guidelines should be created.
Further, the requirements state that all national specific information from the current building specification should be included in CityGML Sve-Test together with the CoClass code from the Swedish construction classification system and the possibility to have external referencing to registers. These requirements are fulfilled as the corresponding attributes were added to CityGML Sve-Test. This is also the case with the additional information needed in the building permit process.
7.3. Creation of Test Data
The study area was around the construction project of a kindergarten in the city of Karlstad in Sweden, called Lotsen. Three datasets were used:
a BIM model in IFC format, hereafter called LotsenIFC;
3D geodata buildings surrounding the building Lotsen in DWG format, hereafter called ExistingBuDWG;
the detailed development plan of the area in GML format, hereafter called DetailedDevPlan
Besides data for the study area around Lotsen we also used a BIM-model from Falun, Sweden, denoted Myran. This BIM model describes a vehicle inspection building.
is an IFC architecture model exported from Autodesk Revit 2018 in IFC 2x3 format (as the model could not be correctly exported to IFC 4 due to problems with curved walls, Figure 7
). The BIM model, LotsenIFC
, was transformed from a local coordinate system relative to the building model, to a correctly georeferenced model using the project base point in Sweref 99 13 30 (EPSG:3008) which is the official municipality system. All the building objects in the BIM model that have linkage to CityGML Sve-Test were classified with CoClass in Revit before exporting it as an IFC file.
The 3D DWG (Autodesk AutoCAD), ExistingBuDWG
, was provided from the city of Karlstad to represent the existing buildings in the area (see Figure 8
). The buildings did not have any building id, which was solved by dissolving the 3D building geometries into a surface footprint for each building and then a spatial join between the original 3D geometries and the 2D surface footprint was performed to set an id on every building. Some of the building faces were wrongly oriented but were not fixed in the project (cf. Figure 8
The detailed development plan, DetailedDevPlan
, conforms to the Swedish standard for computer readable plans [61
] and was obtained from the city of Karlstad (with support from the National Board of Housing, Building and Planning) as a GML file. No modifications were made on this dataset.
7.4. Conversion of BIM to CityGML Sve-Test
were converted to CityGML Sve-Test format. LotsenIFC was converted to both LOD1 and LOD2 models while ExistingBuDWG
was only converted to LOD1. The conversion was performed with the extract, transform and load (ETL) tool Feature Manipulation Engine (FME) from SAFE Software (https://www.safe.com/
) and the results of the conversation can be seen in Figure 9
To create an LOD1 model is relatively simple, a building footprint is created and set to the lowest point of the building and extruded to the highest point of the building to create a valid building solid. The creation of a LOD2 model is more complicated as it is based on that the roof is kept intact and that new walls are created and extruded downwards. The solids created are dissolved into one (or few) main solid that represents the entire building. In this building, the walls were outside the roof, so the conversion had to use both the roof and the top of the walls to create a building solid. Difficulties in dissolving the wall and roof geometry resulted in some unremoved inner walls (Figure 10
The CoClass classification was useful in the translation of IFC building objects to CityGML Sve-Test. It simplified the selection of correct building objects and geometries. The selection was used to create the relevant CityGML Sve-Test attributes such as bounded by, areas, and building UUID. The hierarchical structure of CityGML Sve-Test consisting of city model, building, building part, roof surface, and wall surface was then created. Cross validation between IFC attributes and CoClass classification was used in the project. For instance, controlling if both CoClass and IFC attributes include information regarding if a wall is external or not will make it safer compared to using only one source.
The GML-geometries for LotsenIFC and ExistingBuDWG files were created using FMEs built-in transformers and finally, the attributes of CityGML Sve-Test were added and GML files were written with a text writer in FME since no native CityGML 3.0 writer exists. The files were later used in the test for building permit applications.
7.5. Using CityGML Sve-Test for Building Permit Applications
A test case was performed to study if CityGML Sve-Test can facilitate automated checks of building permit applications, more specifically if the standard supports automated checks of requirements in a detailed development plan (Figure 11
First the detailed development plan, DetailedDevPlan
, was imported into FME with a script that was previously created within the project Får Jag Lov
? coordinated by Boverket (the National Board of Housing, Building and Planning) (see [55
]; FME script available on GitHub: github.com/TestbedLU). The dataset LotsenLOD1GML
was imported into FME (Figure 12
a) using a general XML-reader. The geometry was extracted with a GeometryExtractor
transformer and the area where the building will be located according to the building permit application was identified (Figure 12
b). The existing regulations in the area were obtained from the detailed development plan (Figure 13
). In this case study, one regulation was related to function of the building and two regulations were related to the properties of the building (number of storys and level of densification—defined as the building area divided with the area of a specific region). These regulations were categorized into two lists: one for regulations related to function (upper) and one for regulations related to building property (lower) in Figure 13
The test of the regulations was performed in a Python-script embedded in FME that also generates a report in Excel. In Sweden the around 270 regulations that can be included in a detailed development plan are listed as codes in a criteria list. Around 85% of these can be automatically checked [55
]. As an example, the code DP_KM_S_For
(upper regulation in Figure 14
) states that the function of a building must be kindergarten (swe: Förskola
). The Python script loops over the lists of regulations and checks all existing regulations against the code attribute in the LotsenLOD1GML
The test case shows that it is possible to use an automated method to check if a building in CityGML Sve-Test format conforms to the regulations in a detailed development plan. The test case only included three regulations, but it still shows potential advantages of the extending CityGML with an ADE. The attribute byggnadArea (building area) that was used to calculate the level of densification is part of the created ADE. Other CityGML attributes such as function, for checking the function of the building, and storeysAboveGround for checking the maximum number of building storys were also used.
The attribute coClass that is part of the created ADE includes a CoClass classification value and this can facilitate automated checks of building permits. It can be a support when checking the function of a building; and since this code is present in both the IFC and geodata models it can also facilitate the linkage between the models within the building permit process.
The building in this test has a flat roof but other roof types, such as gable roof, and regulations related to roof angle are common in detailed development plans. Even though the roof angle can be calculated from a LOD2 (and higher LOD) building model it is an advantage to check the roof angle based on attribute instead of involving calculations based on geometries. This will be possible using CityGML Sve-Test as it includes the attribute roof angle.
7.6. Importing CityGML Sve-Test to Software Tools
Another test case was to import test data in CityGML Sve-Test format into two commercial software tools, for visualization of geometry as well as attributes. The two software were S-Visualizer from Complete3D and Revit from Autodesk.
The 3D visualization tool S-Visualizer can import e.g., raster, vector, 3D surfaces (mesh), point clouds, and supports analyses, such as modelling of solar radiation and water levels. Within this study, an import function for the CityGML3 Sve-Test format was developed. Figure 14
shows that both geometry and attribute data from the datasets LotsenLOD1GML
can be displayed with S-Visualizer.
The test in Revit was performed by Symetri, a reseller of Autodesk Revit who also develop Swedish adaptations for Revit. As part of this study, Symetri developed procedures for importing CityGML3 Sve-Test into Revit. The dataset ExistingBuGML
was successfully imported and the result is shown in Figure 15
. Some experiences from the work is that coordinates must be transformed to a local coordinate system upon import; the best geometric conformity is achieved with Direct Shapes
(a format that does not allow further editing); adding the required attribute Properties
is straight forward, and the values of those attributes can be modified; Revit does not have built-in support for code list management, this would require an extension; finally how the object hierarchy from CityGML should be recreated in Revit requires further investigation.
7.7. 3D Cadaster
A study by [52
] established technical and legal solutions for the AEC companies, the cadastral surveying units, and city-surveying units to share information for handling 3D cadaster information. Their method was based on the open standards LADM, IFC, and CityGML 3.0. The cadaster attribute information was stored in LADM, while the physical extent of the cadaster units (as well as the easements) was stored in IFC. The IFC data (both building and cadaster borders) were converted to CtiyGML3 and integrated to an existing city model (Figure 16
). This approach enabled visualization of the cadaster information on a city scale (corresponding to a 3D cadaster index map), as well as macro analysis of cadaster information, by linking the CityGML 3.0 data to LADM. In the study it was shown that by utilizing the AbstractSpace
in CityGML 3.0 it was possible to perform this linkage without extending CityGML with an ADE (cf. work by [24
], who created an ADE for CityGML 2.0 for a similar purpose).
The study by [52
] was based on CityGML 3.0 (without any ADE), and not CityGML Sve-Test. Nevertheless, the study shows the capability of CityGML 3.0 for linking physical and legal information, and that CityGML 3.0 can be used as a base for a 3D cadastral index map. Since CityGML Sve-Test is a superset of CityGML 3.0 this capability is guaranteed also in this model.
8.1. Choice of Standard
From our perspective a national building standard should be based on CityGML as this is an open and comprehensive standard that is well established [6
]. However, the selection of the current official version 2.0 or the new proposed version 3.0 is an open question. Version 2.0 is more mature and it is supported by a number of software while version 3.0 includes many new and promising features. This is shown in the example where the logical space concept is utilized for 3D cadaster applications. The new feature BuildingConstructiveElement
is also interesting as it allows for direct mapping of constructive elements from IFC (e.g., IfcRoof
, and IfcWall
). This together with the use of the CoClass classification can enhance the transformation from IFC models. CoClass might also be interesting from an international perspective as up to this date, five countries have signed a letter of intention to explore possibilities to develop a common environment classification system with CoClass in their countries.
However, there are also disadvantages to using CityGML 3.0 and the new features that come with it. Already, CityGML 2.0 is often regarded as a complex and too broad standard and therefore it has not been implemented—in its entirety—by many GIS software vendors. The new extended version 3.0 will likely increase the complexity in implementing and validating CityGML files. Irrespective of the CityGML version, the next question is whether the model should be extended with additional information using an ADE, or not. According to [26
] an advantage with ADEs is that it makes it possible to add more application specific information while disadvantages are that it adds complexity to the model and that there is few software that can entirely interpret ADEs.
Another option for a national 3D city model standard is CityJSON, a JSON implementation of a subset of the CityGML 2.0 data model. According to [62
], disadvantages with CityGML are the complex and verbose GML encoding that both make it difficult to parse files and for developers to implement. In CityJSON, all hierarchies are removed, and the geometries are simplified. JSON is favored by many developers as its data structure is used in many programming languages. JSON is also one of the preferred formats for data exchange on the web. CityJSON is relatively new and is not an official OGC standard, but it can be seen as an exchange format for CityGML.
8.2. Information Architecture
Sweden plans to take a two-layer approach in the development of standards for 3D geodata. The first layer contains a conceptual model that includes “all” information needed for the built environment, but with no mention of any international standards or formats. The second layer represents the data exchange with a distinction between bidirectional data exchange between two predefined parties where update is allowed; and the provision of data to different actors. The CityGML Sve-Test is proposed to be part of this layer and it should be possible to add additional data formats both for data provision and for data exchange. Examples of such formats are JSON and possibly also linked data in the future. Furthermore, the current plan is not to include any specific layer for restricting the data content, but the need to have surveying and modelling guidelines is clearly stated.
The Swedish two-layer approach could be compared to the ongoing standardization work of 3D geodata in the Netherlands. The authors of [63
] want to simplify this standardization by proposing a three-layer approach. Here, the first layer is a conceptual model that to a large extent conforms to standards, e.g., CityGML and national standards. The second layer includes modelling constraints on the conceptual model to limit it for a specific purpose, e.g., to restrict the geometry types or limit the use of certain objects. Finally, the third layer defines the encoding formats for data exchange, e.g., XML/GML, CityJSON, or JSON-LD (to allow linked data properties in JSON). The authors of [63
] anticipate that such 3D standardization framework is more flexible and will thereby simplify the implementation of 3D city models.
Neither of the above-mentioned examples provide a presentation layer, i.e., a layer including details of the cartographic solution. This layer is in many practical applications important and could act as a fourth layer.
8.3. Purposes of 3D City Models
Many of the choices described above boil down to what the building information should be used for. In [3
] the authors analyzed the functionality and usability of 19 Finnish 3D city models and conclude that many models do not live up to the expectations, especially not to the expectation of being a multipurpose digital platform that can serve various and differentiated needs for city officials, citizens, and organizations. To overcome this, Julin et al. suggest a concept for harmonizing 3D city modelling that includes and combines three different techniques for 3D city modelling: 3D GIS, BIM, and computer graphics. The authors of [14
], on the other hand, suggest that a 3D city model should not include more than what is needed for its intended purpose and propose five BIM-GIS integration levels of the models depending on what the application should be used for.
In Sweden there is now a strong focus on the digitalization of the planning and building process, among others to automate the building permit process. Here, the building theme plays an important role and the Swedish building specification needs to be revised to include the new requirements. The main focus of CityGML Sve-Test is applications for the planning and building process, but it should also be possible to extend the model with information for additional applications, e.g., noise and energy analysis or navigation. This can be done either by extending an existing theme with additional information, or by extending the model with additional themes (e.g., city furniture, tunnels, and bridges). Such extensions will be facilitated and also more harmonized if a comprehensive standard like CityGML is used.
Both having a very comprehensive 3D city model and a more minimalistic one has advantages and disadvantages. In a comprehensive model “everything” needed can be included, e.g., CityGML includes modules for buildings, tunnels, bridges, city furniture, and vegetation. It is therefore relatively simple to add new applications. Disadvantages with such model is that it can be difficult to implement and to use. A more minimalistic model is easier to implement and to use. Disadvantages here are that it can be difficult to foresee all possible usages and to fit in new applications without changing the model.
8.4. Versioning of 3D City Models
The lifecycle perspective is another important aspect for buildings and 3D city models that are used in urban planning. For example, objects in a city (e.g., buildings, tunnels, and bridges) are planned, constructed, renovated, and demolished; in the planning process it could be desirable to visualize different alternative versions of buildings when planning a new construction; when BIM data is used as the source for a 3D city model, one needs to know when these models were synchronized. That is, there are many different lifecycle aspects and they need to be considered when implementing a 3D city model. Some examples in the literature where this is described are in CityGML 3.0 where a new versioning module is added [64
], and a new approach for versioning of 3D city models in CityJSON is proposed by [65
]. To use the Product Lifecycle Support standard [66
] is another approach described by [67
]. Lifecycle management is not included in this study but needs to be tested and evaluated in future studies.
In this study we developed a proposal for a Swedish building standard, CityGML Sve-Test. It was developed as an ADE of CityGML and we chose to use the new proposed version 3.0 of CityGML as this version includes many new features that are of interest from a Swedish perspective. For example, the new space concept distinguishes between physical and logical spaces, where the logical spaces could represent the legal spaces of the 3D cadaster; and the enhanced possibilities to more easily convert data and to link to other standards such as IFC and LADM. CityGML Sve-Test also includes the Swedish classification system CoClass [38
] both to improve the definition of terms and to facilitate interoperability with other urban processes. To overcome the difficulties of using a comprehensive standard, it is important to develop and use detailed guidelines that describe how objects in the city model should be added and updated, as well as what to include from the model when providing the information to various actors.
The test cases performed in the study show that it is possible to convert an IFC model to a CityGML Sve-Test dataset and that the use of CoClass can facilitate this conversion. It was shown that a CityGML Sve-Test dataset can be used to automatically check if a building conforms to the regulations in a detailed development plan. It was also possible to import and visualize CityGML Sve-Test datasets in the commercial software S-Visualizer and Revit. Finally, the authors of [52
] showed that CityGML 3.0 has the capability to link to legal information in the LADM standard, that cadastral information can be visualized using CityGML 3.0, and that it can be used as a base for a 3D cadastral index map.
There are various options for 3D city models, all having advantages and disadvantages. We assume that the need for national coordination of 3D city models will increase with the number of complex models within a country. We believe that to have a successful national implementation of building and 3D city model standards, it is important to specify what the models should support, that is what should they be used for, and how complex should they be. The implementation should then settle on a reasonable level. We also suggest that the building and 3D city models, or at least their data models, should conform to an international standard, e.g., CityGML. The exchange format (XML/GML, JSON etc.) might change in the future but to build on a well-established and standardized data model will ensure that the models both have a harmonized structure and harmonized concepts. If a classification system exists, it should be included in the standard to improve definition of terms and to facilitate the interoperability with BIM data. The standard should also be complemented with measuring guidelines to ensure a more conforming creation of the objects included in the standard.