WO2023096588A1

WO2023096588A1 - A system, a method and a computer program for construction progress monitoring

Info

Publication number: WO2023096588A1
Application number: PCT/SI2022/050031
Authority: WO
Inventors: Zoran PUCKO; Danijel REBOLJ
Original assignee: Univerza V Mariboru
Priority date: 2021-11-25
Filing date: 2022-11-25
Publication date: 2023-06-01

Abstract

A computer implemented method for construction progress monitoring uses a mobile device. The mobile device comprises a mobile processor. The mobile device further comprises a mobile memory and a scanner unit both functionally coupled to the mobile processor. In addition, the mobile device comprises a receiver and a sender both functionally coupled to the mobile memory. The method comprises receiving, using the receiver, at least a part of a building information model of a building to be constructed. The at least part of the building information model comprises a first plurality of model elements, each with a descriptor. The at least part of the building information model is stored to the mobile memory. The method further comprises acquiring, using the scanner unit, a spatial information of a construction site of the building to be constructed, and comparing, using the mobile processor, the spatial information and a model element of the first plurality to decide whether a section corresponding to the model element exists in the spatial information. If the section corresponding to the model element exists, the method further comprises sending, using the sender, at least part of the descriptor of the model element for updating a model of the construction site.

Description

A system, a method and a computer program for construction progress monitoring

Technical field

The disclosure relates to automated construction site monitoring, in particular to a computer implemented method for construction site monitoring, in particular using a building information model.

Background

The construction of a building is a multi-stage process. Early stages involve the construction of large building elements, such as floors, walls or ceilings. Later stages typically involve smaller elements such as doors, windows or railings, or even smaller elements related to electrical, lighting or sanitary installations. The stages or individual construction steps thereof may build up on each other and be intertwined. For example, the installation of a door may rely on the presence of a wall; or tiling a wall may rely on electrical or water installations therein being finalized. To improve the efficiency of the construction, a detailed plan with all elements involved is developed beforehand. The plan also contains an order and a timeline of the installation of the elements. A computer implementation of such a plan is referred to as a building information model, more specifically a four-dimensional building information model. Therein, three dimensions refer to the spatial arrangement of the elements already installed at a given point in time during the construction. The fourth dimension refers to the timeline. The actual construction may be affected by a delay of an installation of an individual element. As the construction steps are intertwined, the delay may cause follow-up delays and/or followup costs. For example, a machine for a subsequent construction step, which can not yet be performed, may be provided at the site of the subsequent construction step and idle rather than being used for a different task. The efficiency enhancement related to the building information model may further be improved by updating and re-optimizing the model as quickly as possible after the delay has occurred. According to the updated and re-optimized model, the machine may then first be used for the different task. Only after the delayed installation has finally been completed, the machine is provided at the site of the subsequent construction step. Similarly, construction materials and workforce may be redirected to those construction steps they can promote in the most efficient way. The faster the delay is detected, the more time remains for updating the building information model as well as for organizing and implementing the modifications of the construction steps. In the example, reallocating the machine prior to its transport to the site of the hindered subsequent construction step may save machine time and expenses related to the transport. Detecting the delay is based on a comparison between the building information model and the status of the (physical) construction site. Monitoring the latter at a high frequency, or with a minimum lag with respect to construction progress and delays, respectively, remains an open problem in the state of the art.

In conventional construction progress monitoring, at least one (human) expert visits and inspects the construction site. The inspection takes around a workday, causes significant costs and is typically performed at most on a weekly basis. To improve the frequency, assistive devices to support the menu inspection have been developed. For example, each construction site element may carry an identifier such as an RFID tag, which may be inventoried by a non-expert during the inspection or already when the element is installed on the construction site. While this approach can reduce the time lag in the monitoring, it still requires significant manual action.

US2019/0325089A describes a system wherein a computer system with a graphical user interface provides images of the construction site or point clouds constructed from the images. Construction progress and delays are identified by a human expert inspecting the images or point clouds alternatively or in addition to inspecting the construction site itself. According to an approach described in the state of the art, images of the construction site may be provided by a stationary device or a robot with a camera, such as an unmanned aerial vehicle, on the construction site.

Description of the solution to the technical problem

In view of the technical problems described above, there is a need for an automated construction site monitoring, which provides a status of a construction site at a high frequency or even continuously, i. e. at a rate similar to the typical time scale of the progress on a physical construction site. This objective is achieved with a method according to independent claim 10 and a corresponding computer program according to claim 13. Independent claim provide a system comprising a mobile device and a server for executing the method. The dependent claims relate to preferred embodiments.

In a first aspect, the system comprises:

- at least one mobile device comprising: o a mobile processor, o a mobile memory and a scanner unit both functionally coupled to the mobile processor, o a receiver and a sender both functionally coupled to the mobile memory;

- and a server comprising: o a server processor and a server memory functionally coupled to the server processor, said server being connectable to the at least one mobile device, wherein the server is provided with a building information model of the building to be constructed and the model of the construction site on the server memory,

- wherein the at least one mobile device is configured to execute at least the following operations: o receiving using the receiver and storing using the mobile memory at least a part of the building information model of the building to be constructed sent by the server, wherein the at least part of the building information model comprises a first plurality of model elements, each equipped with a descriptor, o acquiring using the scanner unit a spatial information of a construction site of the building to be constructed; o comparing, using the mobile processor, the spatial information and a model element of the first plurality to decide whether a section corresponding to the model element exists in the spatial information; and o if the section corresponding to the model element exists the at least one mobile device is configured to send using the sender at least a part of the descriptor of the model element to the server for updating the model of the construction site stored on the server,

- and wherein the server is configured to execute at least the following operations: o receiving at least part of the descriptor of the model element sent by the mobile device and storing it to the server memory; and o updating, using the server processor and the at least part of the descriptor of the model element, the model of the construction site, in order to track progress of the building contruction process.

The system for automized continuous monitoring of construction process in real time and comprises the mobile device for taking depth images (RGB-D images) of the construction site to determine which elements have been constructed, the server having the construction plan and receiving descriptors about the constructed elements used for updating the construction plan. The construction plan is a governing document that defines how a project is to be executed, monitored, and controlled. It establishes exactly how the project execution phase of the project will be managed to meet the requirements of the project and is also called a contruction execution plan. A computer implementation of the construction execution plan is referred to as a building information model (BIM), more specifically a four-dimensional building information model (4D BIM). Therein, three dimensions refer to the spatial arrangement of the elements and it is called 3D BIM. The fourth dimension refers to the timeline and the descriptor typically includes a target installation date, thus extending the 3D BIM into a four-dimensional BIM (4D BIM). In the design phase, a detailed execution plan (4D BIM) is developed beforehand and is known as 4D As- design BIM and represents a building information model of a building to be constructed. In the construction phase, i.e. when where desired to determine the actual state of the construction site, a building information model of the construction site is created and is known as 4D As-built BIM and represents the target state of the construction site of the building at any moment during the construction progress. To improve the efficiency of the construction, these two 4D BIM models has to be compared to identify possible discrepancies with the system in a unique way, as described below. The system is supported by a method performed by the mobile device and the server as well as a computer program encoding said method. The invention replaces the manual monitoring process and/or the previously known methods for tracking construction progress that used to scan the whole construction site and searched for the newly constructed parts. Known methods only scanned the whole construction site, which causes significant amount of data, many taken images that have to be transformed into Pont Cloud (size of several GB), and thus technically demanding processing of the data. On the contrary, the invention is used to scan the construction site only at parts, which are actively built. The mobile device automatically captures depth images (RGB-D images) and converts them into a point cloud, which is instantly used for element identification process and discarded afterwards. The only data that is stored and sent to the server are the descriptors of the identified elements. These are preferably in TXT files, whereby each descriptor comprises at least an ID of the element, which is automatically assigned to each BIM element in the whole As-design 3D BIM model and is thus unique for each element. The TXT file, i.e., the descriptor, is then sent to the server for updating the construction plan to mark built elements. This approach also improves security, as the element ID cannot be used to determine the identity of the worker who took the scan (image) and/or the people in the taken image are not visible, as the image is not stored.

The method as the second aspect of the invention comprises receiving, using the receiver, at least a part of a building information model of a building to be constructed. The at least part of the building information model comprises a first plurality of model elements, each with a descriptor. The at least part of the building information model is stored to the mobile memory. The method further comprises acquiring, using the scanner unit, a spatial information of a construction site of the building to be constructed, and comparing, using the mobile processor, the spatial information and a model element of the first plurality to decide whether a section corresponding to the model element exists in the spatial information. If the section corresponding to the model element exists, the method further comprises sending, using the sender, at least a part of the descriptor of the model element for updating a model of the construction site. The method provides a distributed approach to construction site monitoring. Using mobile devices, any progress at a construction site is detected as it occurs. Moreover, the progress is analyzed by the mobile device along with its detection. Therefore, the analysis may be performed at a rate similar to or faster than the rate at which the progress of the construction site occurs. In particular, sending large data sets sent from mobile devices to a central computer may be avoided. Large data sets sent in the state of the art may cause problems processing these large data sets, for example by merging them, which is a computationally demanding process. In the method according to the disclosure, the mobile device sends only a small amount of data, such as a part of a descriptor unique to the detected element or a list of descriptors reflecting a plurality of detected elements, where each descriptor in the list is unique to one of the elements. The small amount of data can be processed quickly and efficiently by the mobile devices in a mesh network or by a server system, for example to update a model of the construction site, also referred to as an as-built building information model. The method may therefore provide a continuous construction site monitoring with an updating of the as-built building information model at a rate comparable to the progress at the construction site.

The adjective “mobile” may comprise “battery-operated” and/or “light-weight”, in particular with a weight of at most 200 g. The mobile device may be or comprise a wearable electronic, in particular an electronic helmet, such as an electronic hard hat. Alternatively, the mobile device may be a device suitable for mounting on a mobile work equipment, on a construction machinery, or on a construction or inspection robot.

The model element may be digital representation of a three-dimensional structure or a twodimensional surface. In particular, the three-dimensional structure may be a physical building element or construction element. The two-dimensional surface may be a surface of the physical building element or the construction element.

The descriptor may comprise one or all of the following: a unique element identifier, a model element location, an element type identifier, a target installation date, an installation date, a binary indicator of the presence of the model element.

The building information model may be a set of model elements with descriptors, sufficient to describe all essential elements of the building to be constructed.

The model of the construction site may be a second building information model and/or an asbuilt building information model. In particular, the model of the construction site may be similar or identical to the building information model, comprising at least a binary indicator of the presence of each model element already installed. Alternative or in addition, one or every model element of the model of the construction site already installed may have a descriptor referring to an installation date. Alternative, the model of the construction site may be different from the building information model, for example in its file format, but also comprise model elements with descriptors, sufficient to describe all essential elements present at the construction site and/or already installed at their corresponding model element locations.

The at least part of the descriptor of the model element may be unique to the model element and/or be suitable to uniquely identify the model element. The at least part of the descriptor of the model element may be different from a corresponding part of a second descriptor of a second element of the first plurality of model elements whenever the first element and the second element are different from one another.

The spatial information may be or comprise a three-dimensional spatial information. Acquiring the spatial information may comprise recording a plurality of camera images or measuring distances, for example using a laser-based distance measurement. Acquiring the spatial information may further comprise generating a point cloud from the plurality of camera images or from the distances, in particular using the mobile processor. The spatial information may refer to the point cloud.

The sender (receiver) may use at least one wireless connection, for example WiFi, Bluetooth (low energy), a 2.4 GHz sender and/or receiver, Zigbee, or Z-Wave. Alternatively or in addition, the sender (receiver) may provide a connector for a wired connection such as USB, (e)SATA, Thunderbolt, or Firewire. In particular, the sender (receiver) may provide a connector for a docking station. Alternatively or in addition, the sender (receiver) may comprise a storage medium removable from the mobile device, such as a flash memory or an optical, magnetic or magnetooptical data storage.

The method may further comprise, if the section corresponding to the model element exists: Determining, using the mobile processor, a relative position of the section corresponding to the model element within the spatial information. The method may optionally comprise sending the relative position of the section corresponding to the model element along with the at least part of the descriptor. The relative position may be relative to other objects identified in the spatial information, and/or to boundaries of the spatial information. The descriptor may comprise a model element location, and the method may further comprise comparing, using the mobile processor, the at least part of the building information model and the spatial information to identify an overlap region. The method may further comprise determining, using the mobile processor and the overlap region, a relative position of the model element within the spatial information. The method may further comprise, if the section corresponding to the model element exists:Calculating, using the mobile processor, a location deviation between the relative position of the model element and the relative position of the section corresponding to the model element; storing the location deviation on the mobile memory; and optionally sending the at least part of the descriptor only if the relative position of the model element and the relative position of the section corresponding to the model element essentially match. In embodiments with a measured location, the method may further comprise correcting the measured location accounting for the location deviation to obtain a corrected measured location.

The building information model may be related to a static coordinate system. The mobile device may further comprise a localization unit. The method may further comprise: Providing, using the localization unit, a measured location for the spatial information relative to the static coordinate system; and, if the section corresponding to the model element exists: Referencing the relative position of the section corresponding to the model element to the static coordinate system using the measured location, and determining an absolute position of the section corresponding to the model element within the static coordinate system; and optionally sending the absolute position of the section corresponding to the model element along with the at least part of the descriptor. The measured location may reflect the location of the scanner unit at the construction site, both in terms of its position (three degrees of freedom) and its orientation (three degrees of freedom) in three-dimensional space. The measured location and/or the location of the scanner may refer to a coordinate system of the construction site, spanned, for example, by a vertical direction and a longitude and an altitude, a boundary of a construction site, or a northsouth direction and an east-west direction. Building information models typically refer to a static coordinate system of the building information model with an origin set in the model, which is related to the coordinate system of the construction site in a known way. Therefore, the measured location and/or the location of the scanner provided by the localization unit may be related to the static coordinate system of the building information modeland vice versa. The localization unit may use both relative location referencing, which may provide a measured location relative to a previously measured location, and absolute location referencing. The relative location referencing may use an inertial measurement unit (IMU), for example using at least one MEMS (micro-electro- mechanical systems) component. The absolute location referencing may use a compass, a GPS (global positioning system) location, a wireless or a wired connection localization, in particular using one of the networks described in the context of the sender (receiver). In particular, the localization unit may use the sender (receiver). For example, the localization unit may be adapted to interact with at least one reference point of the construction site, such as a wireless connection beacon or a connector at a known position of the construction site connecting wirelessly, inductively or through a conductive electrical contact to the localization unit. The referencing may be performed by the mobile processor. Alternatively, the method may comprise sending the measured location from the mobile device, in particular for referencing by an external entity such as a server.

The building information model may be related to a static coordinate system, and the mobile device may comprise a localization unit. The method may further comprise: Providing, using the localization unit, a measured location for the spatial information relative to the static coordinate system; and referencing, using the mobile processor and the measured location, the spatial information to the static coordinate system to obtain an absolute spatial information. The method may further comprise, if the section corresponding to the model element exists: Determining, using the mobile processor and the absolute spatial information, an absolute position of the section corresponding to the model element within the static coordinate system; and optionally sending the absolute position of the section corresponding to the model element along with the at least part of the descriptor. The descriptor may comprise a model element location. The method may further comprise, if the section corresponding to the model element exists: Comparing, using the mobile processor, the model element location and the absolute position of the section corresponding to the model element; and optionally sending a result of the comparison along with the descriptor, or sending the at least part of the descriptor only if the model element location and the absolute position of the section corresponding to the model element essentially match.

The method may further comprises calculating, if the model element location and the absolute position of the section corresponding to the model element essentially match, using the mobile processor, a location deviation between the model element location and the absolute position of the section corresponding to the model element; storing the location deviation on the mobile memory and/ or correcting the measured location accounting for the location deviation to obtain a corrected measured location; and redoing the referencing accounting for the location deviation or the corrected measured location. The method may optionally comprise redoing the determining the absolute position of the section corresponding to the model element within the static coordinate system, in particular prior to the optionally sending the absolute position of the section corresponding to the model element along with the descriptor. Correcting the measured location taking into account the deviation between the model element location and the measured location of the section of the point cloud corresponding to the model element avoids large errors of the extracted (absolute) positions, even if position measurements of the localization unit have a limited accuracy and/or are relative to earlier measurements.

Any or all the process steps of the method may be performed iteratively.

The method may further comprise performing, after they have been finished according to a first iteration, at least a second iteration of the process steps of acquiring the spatial information of the construction site, and comparing a model element of the first plurality and the spatial information to decide whether a section corresponding to the model element exists in the spatial information. According to a first alternative, the method may thereafter comprise performing the following process steps again to determine a measured location for the spatial information of the second iteration and an absolute position of the section corresponding to the model element of the second iteration: Providing, using the localization unit, measured location for the spatial information relative to the static coordinate system; and, if the section corresponding to the model element exists: Determining, using the mobile processor, the relative position of the section corresponding to the model element within the spatial information; optionally sending the relative position of the section corresponding to the model element along with the at least part of the descriptor; referencing the relative position of the section corresponding to the model element to the static coordinate system using the measured location, and determining an absolute position of the section corresponding to the model element within the static coordinate system; and optionally sending the absolute position of the section corresponding to the model element along with the at least part of the descriptor.

According to a second alternative, the method may comprise performing the following process steps again to determine a measured location for the spatial information of the second iteration and an absolute position of the section corresponding to the model element of the second iteration: Providing, using the localization unit, a measured location for the spatial information relative to the static coordinate system; referencing, using the mobile processor and the measured location, the spatial information to the static coordinate system to obtain an absolute spatial information; and, if the section corresponding to the model element exists: determining, using the mobile processor and the absolute spatial information, an absolute position of the section corresponding to the model element within the static coordinate system; and optionally sending the absolute position of the section corresponding to the model element along with the at least part of the descriptor. The method may further comprise correcting the measured location for the spatial information of the second iteration and/or the absolute position of the section corresponding to the model element of the second iteration accounting for the location deviation of the first iteration. A correction from the previous iteration may be used in the subsequent iteration.

The method may further comprise comparing, using the mobile processor, a second model element of the first plurality and the spatial information to decide whether a section corresponding to the second model element exists in the spatial information; and if the section corresponding to the second model element exists: Sending, using the sender, the descriptor of the second model element for updating a model of the construction site. The model of the construction site may comprise or be an as-built building information model. In addition to the first model element, the second model element may be taken into account to improve the precision of the absolute positions and/or, in embodiments with a correction, to improve an accuracy of the location deviation. A relative position of the section corresponding to the second model element may be determined as described for the relative position of the section corresponding to the model element. An absolute position of the section corresponding to the second model element may be determined as described for the absolute position of the section corresponding to the model element. A second model element location and the absolute position of the section corresponding to the second model element may be compared and a second location deviation between the second model element location and the absolute position of the section corresponding to the second model element may be calculated as disclosed in the context of the model element. The measured location may be corrected accounting for the location deviation and the second location deviation; or the location deviation and the second location deviation may be stored on the mobile memory and be accounted for in redoing the referencing according to the second iteration. In analogy to the second model element, further model elements of the first plurality may be taken into account to further improve the precision of the absolute positions.

The method may further comprise generating an element time stamp associated with the section corresponding to the model element, and sending the element time stamp together with the at least part of the descriptor. The element time stamp may, for example, be associated with acquiring the spatial information, or with comparing the model element and the spatial information and indicate when the model element was detected, also giving an approximation for the time when it was installed. A list may be stored on the mobile memory, and the method may further comprise storing, whenever a comparing finds that a section corresponding to a model element exists, at least one of the following in the list: At least a part of the descriptor of the model element, the relative position of the section corresponding to the model element, the absolute position of the section corresponding to the model element, the element time stamp, the result of comparing the model element location and the absolute position of the section corresponding to the model element, the location deviation between the model element location and the absolute position of the section corresponding to the model element; and the corrected measured location accounting for the location deviation. The storing may only be performed when the at least part of the descriptor is not yet in the list. The list (e. g., entire list of detected element positions) may be used in the correction to further improve the precision of the relative positions or the absolute positions. The list may be sent at time intervals on the order of minutes or hours to avoid a need for a permanent wireless connection.

The method may further use at least one server, the at least one server comprising a server processor and a server memory functionally coupled to the server processor, and the method may further comprise storing the building information model of the building to be constructed and the model of the construction site on the server memory; sending, using the at least one server and prior to the receiving the at least part of the building information model using the receiver, the at least part of the building information model from the server memory; receiving, after the sending the at least part of the descriptor of the model element using the sender, the at least part of the descriptor of the model element at the at least one server and storing it to the server memory; and updating, using the server processor and the at least part of the descriptor of the model element, the model of the construction site. The server may provide the building information modeland keep the model of the construction site updated. The two models may use the same data format. The server may comprise several computers. For example, one computer may perform the sending and receiving, and one computer may perform the updating the model of the construction site. At least one of the computers may be a mobile computer. The server may generate the time stamp upon receiving the at least part of the descriptor and store it along with the at least part of the descriptor to the server memory. Updating the model of the construction site may comprise adjusting at least one descriptor of a model element of a building information model of the construction site, for example an installation date or a binary indicator of the presence of the model element.

In embodiments wherein the mobile device sends the relative (or absolute) position of the section corresponding to the model element along with the at least part of the descriptor, the method may further comprise receiving the relative (or absolute) position of the section corresponding to the model element by the server. In such embodiments, updating the model of the construction site may comprise comparing the relative (or absolute) position of the section corresponding to the model element to the building information model. In particular, a plurality of relative (or absolute) positions corresponding to a plurality of model elements may be sent by the mobile device and received by the server, and updating the model of the construction site may comprise comparing the plurality of relative (or absolute) positions to the building information model, in particular to assemble the model of the construction site.

The method may further use an additional mobile device comprising an additional mobile processor, an additional mobile memory and an additional scanner unit both functionally coupled to the additional mobile processor, an additional receiver and an additional sender both functionally coupled to the additional mobile memory. The method may further comprise: Sending at least a second part of the building information model from the server memory; receiving, using the additional receiver, the at least second part of the building information model comprising a second plurality of model elements, each with a descriptor; storing the at least second part of the building information model to the additional mobile memory; acquiring, using the additional scanner unit, an additional spatial information of the construction site; comparing, using the additional mobile processor, a model element of the second plurality and the additional spatial information to decide whether a section corresponding to the model element of the second plurality exists in the additional spatial information. The method may further comprise, if the section corresponding to the model element of the second plurality exists: Sending, using the additional sender, at least part of the descriptor of the model element of the second plurality for updating the model of the construction site; receiving the at least part of the descriptor of the model element of the second plurality at the at least one server and storing it to the server memory. The method may further comprise, if the section corresponding to the model element of the first plurality exists: Using the descriptor of the model element of the second plurality in addition to the server processor and the at least part of the descriptor of the model element in the updating the model of the construction site.

The additional mobile device may be characterized by features corresponding to the ones described in the context of the mobile device. The model element of the second plurality may be characterized by features corresponding to the ones described in the context of the model element of the first plurality. For example, the descriptor of the model element of the second plurality may be characterized by features corresponding to the ones described in the context of the descriptor of the model element of the first plurality. Providing a plurality of mobile devices, each installation of a construction element may be detected shortly after it occurs. In particular, any worker at the construction site and any autonomous construction site machine which can operate without a worker may be equipped with a mobile device. Despite the large number of mobile devices which may be comprised in the plurality, the method may ensure that the stored amount of data remains small and processable, while fully reflecting the progress at the construction site.

According to a third aspect, a computer program may be adapted to instruct a computer system to execute the method described above.

According to another aspect, the mobile device for construction progress monitoring of a construction site comprises a mobile processor and a receiver adapted to receive at least a part of a building information model of a building to be constructed. The at least part of the building information model comprises a first plurality of model elements, each with a descriptor. The mobile device further comprises a mobile memory functionally coupled to the mobile processor and to the receiver and adapted to store the at least part of the building information model; and a scanner unit functionally coupled to the mobile memory. The mobile device is adapted to acquire, using the scanner unit and the mobile processor, a spatial information of a construction site of the building to be constructed, and to store the spatial information to the mobile memory. The mobile device further comprises a localization unit. The mobile device is adapted to acquire, using the localization unit, a measured location relative to a static coordinate system and to store the measured locationto the mobile memory. The mobile device further comprises a sender functionally coupled to the mobile memory. The mobile device is adapted to compare using the mobile processor, a model element of the first plurality and the spatial information to decide whether a section corresponding to the model element exists in the spatial information; and to send, if the section corresponding to the model element exists, at least part of the descriptor of the model element using the sender. The mobile device may further be adapted to determine a position of the section corresponding to the model element. The position may be an absolute position or a relative position. The mobile device may be adapted to use the mobile processor, the scanner unit and/or the localization unit to determine the position of the section corresponding to the model element. The mobile device may further be adapted to store the position of the section corresponding to the model element to the mobile memory. The position of the section corresponding to the model element may be an absolute position of the section corresponding to the model element or a relative position of the section corresponding to the model element.

The mobile device may be a wearable electronic device, in particular an electronic helmet, in particular an electronic construction site helmet such as an electronic helmet or an electronic hard hat suitable for withstanding a force generated by a weight of 5 kg dropping onto the helmet from a height of 1 m with a force onto a head in the helmet not exceeding 5 kN. The mobile device and its components, the building information model, and the spatial information may be characterized by features corresponding to some or all of the features described in the context of the method according to the first aspect.

According to another aspect, the server comprises a server processor; a server memory functionally coupled to the server processor; a building information model of a building to be constructed stored on the server memory, wherein the building information model comprises a first plurality of model elements, each with a descriptor; a model of a construction site of the building to be constructed stored on the server memory; a server sending element adapted to send at least a part of the building information model; and a server receiving element functionally coupled to the server memory and adapted to receive at least a part of a descriptor, and to store it to the server memory. The server is adapted to compare, using the server processor, the at least part of the descriptor and the descriptor of at least one model element of the first plurality, and, if they match, to update the model of the construction site using the server processor and the at least part of the descriptor. The building information model, in particular the descriptors, may be characterized by features corresponding to some or all of the features described in the context of the method according to the first aspect.

Brief description of the figures Fig. 1 shows a section of a three-dimensional building information model;

Fig. 2 shows mobile device according to an embodiment;

Fig. 3 shows a construction site with several mobile devices according to an embodiment;

Fig. 4 shows a flow chart of a method according to an embodiment;

Fig. 5 shows a flow chart of a method according to another embodiment;

Fig. 6 shows a flow chart of a method according to yet another embodiment;

Fig. 7A shows a server according to an embodiment and mobile devices according to an embodiment; and

Fig. 7B shows a server and mobile devices according to another embodiment.

Detailed description of embodiments

Fig. 1 shows a section of a building information model (BIM) 100, namely a three-dimensional BIM (3D BIM), of a building to be constructed. The 3D BIM 100 is a computer model of the final building. All construction elements that are to be part of the building are represented by model elements 102, 104, 106 of the BIM 100. As examples, a model element 102 representing a wall, a model element 104 representing a window, and a model element 106 representing a door are indicated. The model elements 102, 104, 106 are three-dimensional objects representing the shapes of the corresponding construction site elements or two-dimensional objects representing their corresponding surfaces. The model elements 102, 104, 106 are developed in a computer- aided design (CAD) software environment, which is also used to assemble the model elements 102, 104, 106 into the 3D BIM. After the assembly with the CAD software, the 3D BIM is stored according to a standardized filed format, the Industry Foundation Classes format, for further data enrichment with descriptors and for data analysis. For each of the elements 102, 104, 106 a descriptor with additional information such as a target location (model element location) is stored in the BIM 100 in the planning of the building. The descriptor typically comprises a target installation date, thus extending the BIM 100 into a four-dimensional BIM (4D BIM), which represents the target state of the construction site of the building at any moment during the construction progress. The descriptor further comprises a unique element identifier and an element type identifier. The element type identifier indicates, for example, a window of a specific type which is too be installed at various locations of the building. In the planning of the building, the planned building and hence the BIM 100 is oriented with respect to a static coordinate system 108, typically with reference to a cardinal direction N.

Fig. 2 shows a mobile device 200 in the form of an electronic hard hat 200 for construction site monitoring. The electronic hard hat 200 is equipped with a scanner unit 202 which contains a camera suitable to produce the point cloud, such as a 3D camera, also referred to as a depth camera. 3D cameras are commercially available. They combine a digital camera with an image processor to construct a (three-dimensional) spatial information in the form of a point cloud using images recorded by the camera. Alternatively or in addition to the digital camera, the scanner units 202 may comprise a device for distance measurements (not shown), such as a laser-based device employing a LIDAR technique. In such an embodiment, the point cloud is constructed from a series of distance measurements. Distance measurements may provide a point cloud with a higher accuracy, yet at a higher cost of the scanner unit 202. The electronic hard hat 200 further comprises a miniaturized computer 204 with a processor 204a and a memory 204b. Computers which are sufficiently miniaturized for integration into the electronic hard hat 200 are known from the state of the art in the form of programmable microcontrollers or single-board computers and available at moderate pricing. In addition, the electronic hard hat 200 comprises a sender and a receiver in the form of a communication interface 206 for sending and receiving data. The communication interface 206 comprises a USB connector to connect the electronic hard hat 200 to a central computer system. The USB connector is also used to recharge a battery (not shown) comprised in the electronic hard hat 200. A docking station is provided, wherein the electronic hard hat 200 is stored during the charging and the sending and receiving of data via the USB connector. In addition, the communication interface 206 comprises a Bluetooth wireless transceiver which is used to establish a wireless connection for example to a repeater, a router, a central computer system or another mobile device 200. The electronic hard hat 200 also comprises a localization unit 208 for providing a measured location of the scanner unit 202. More specifically, the measured location fully describes the position and the orientation of the scanner unit 202 in three-dimensional space and with respect to a static coordinate system of the construction site. The localization unit 208 contains a compass, a GPS unit, and an inertial measurement unit (IMU). The localization unit 208 is further coupled to the Bluetooth transceiver to use the Bluetooth network, if available, for a complementary measurement of the position of the electronic hard hat 200, thus improving the accuracy of the localization. Moreover, when the electronic hard hat 200 is stored in the docking station, the docking station sends its calibrated location to the localization unit 208 using the USB connector to give an additional localization reference. The functionality of the individual components typically requires storing data on a memory and processing data using an electronic processor. The corresponding memory and electronic processor may be provided by the individual components themselves or by one of the other components, in particular by the miniaturized computer 204. For example, according to the depicted embodiment, the point cloud is constructed using the image processor of the scanner unit 202, but it may alternatively be constructed using the processor 204a of the miniaturized computer 204. In the depicted embodiment, the scanner unit 202, the miniaturized computer 204, the communication interface 206, and the localization unit 208 are shown as separate components. However, they may, for example, be integrated on a common board with at least one common processor and/or common memory.

Fig. 3 shows a section of a construction site 100’ at which a number of construction site elements have already been installed. As an example, a wall 102’ is indicated. A window 104’ and a door 106’ are still missing. In addition, Fig. 3 shows various mobile devices 200, 200a, 200b in the form of electronic hard hats 200, 200a, 200b equipped with scanner units 202, 202a, 202b for construction site monitoring. Each scanner unit 202, 202a, 202b has a limited field of view 210, 210a, 210b. Using the numerous hard hats 200, 200a, 200b which are commonly present during construction as platforms for the construction site monitoring, a large portion of the construction site 100’ is monitored in parallel. Consequently, the sections of the construction site 100’ relevant for the construction progress monitoring can be scanned much faster than in a visual inspection by an expert. The field of views 210, 210a, 210b of the scanner units 202, 202a, 202b are typically directed together with the hard hats 200, 200a, 200b at those sections of the construction site 100’ where a construction step is currently being performed. Additional scanner units (not shown) are installed on construction machines, in particular on any autonomous construction site machine which can operate without a worker wearing a hard hat202, 202a, 202b, to cover construction steps performed by the construction machines. Additional scanner units (not shown) can also be installed on mobile work equipment or construction or inspection robots. Therefore, any construction step may be detected while it is being performed. Moreover, as compared to approaches using fixed scanners, the arrangement of the scanner units 202, 202a, 202b according to the disclosure reduces the amount of generated data related to sections of the construction site where no construction step is being performed. Problems addressed in the state of the art are related to merging data obtained by a plurality of scanner units 202, 202a, 202b on a construction site. The mobile devices 200, 200a, 200b of the embodiment of Fig. 3 may quickly generate large amounts of data, in particular on a large construction site 100’ with dozens of scanner units 202, 202a, 202b. To improve the usability of the data, approaches described in the state of the art reference the data sets (images or point clouds) provided by different scanner units to a static coordinate system of a Bl M of the construction site, and then merge the data sets. According to US 2019 / 0325089 A, the merged data set is provided via a graphical user interface for inspection by an expert. According to Z. Pucko, N. Suman, and D. Rebolj, “Automated continuous construction progress monitoring using multiple workplace real time 3D scans,” Advanced Engineering Informatics 38 (2018) 27-40, the merged data set is automatically compared to a 4D BIM. Both solutions provide a merged data set with a reduced redundancy and an improved useability. However, the merging is computationally demanding, in particular when a large number of scanners is involved. Therefore, the implementation of a continuous construction progress monitoring, i. e. wherein the merging is performed at a rate comparable to the rate at which construction site elements are installed, remains an open problem.

Fig. 4 gives a flow chart of a method 300 for construction site monitoring according to the present disclosure, which may be performed by a mobile device similar to the mobile device 200 of Fig. 2 or the mobile devices 200, 200a, 200b of Fig. 3. The mobile device 200, 200a, 200b stores 302 the BIM 100 of the building to be constructed on the memory 204b of its miniaturized computer 204. The BIM 100 has previously been received via the communication interface 206. Typically, the entire BIM 100 is stored. However, in case of an extended construction site, only a part of the BIM 100 may be selected and stored on the memory 204b. The selected section may corresponds to an area in which the person wearing the helmet is supposed to work during a workday, such as an individual building or floor of a building of the construction site. In case of an extended construction site with an available permanent wireless connection, a spatial section of the BIM may be initially stored according to the localization unit 208. When the mobile device 200, 200a, 200b moves and its position according to the localization unit 208 approaches a boundary of the area, the mobile device 200, 200a, 200b downloads a new spatial section of the BIM 100 using the wireless connection. The new spatial section of the BIM 100 may be centered around the boundary which is being approached. As described above in the context of the scanner unit 202, the mobile device 200, 200a, 200b acquires 304 a point cloud by recording 304a images and constructing 304b the point cloud from the images. The point cloud and the BIM 100 stored on the memory are compared 306 by the mobile device 200, 200a shortly after the point cloud is generated, i. e. faster than the time typically needed for a construction step, which is on the order of minutes. In the comparison, sections of the point cloud which correspond to model elements 102, 104, 106 of the BIM 100 are identified. Computational methods for performing the comparison are described in detail in D.Rebolj, Z. Pucko, N. C. Babic, M. Bizjak, and D. Mongus “Point cloud quality requirements for Scan-vs- BIM based automated construction progress monitoring”, Automation in Construction 84 (2017) 323-334. The comparison 306 takes into account only model elements of the BIM 100 which are located within a critical radius around the location of the mobile device 200, 200a, 200b determined by its localization unit 208. The critical radius is determined by the acquisition radius of the scanner unit 202, 202a, 202b and the accuracy of the location determined by the localization unit. The acquisition radius is the maximum distance between the scanner unit 202, 202a, 202b and a captured object, at which a section of the point cloud based on the captured object is constructed reliably. The scanner unit 202, 202a, 202b with the digital camera of the hard hat 200 of Fig. 2 constructs the spatial information of the point cloud reliably when an object in the image recorded by the digital camera is with in an acquisition radius, which depends on the resolution and the processor performance of the 3D camera and may, for example, be up to 25 m from the scanner unit 202, 202a, 202b. As a result of the comparison, the mobile device 202b of Fig. 3 may for example identify that a section of the point cloud generated by its scanner unit 202b capturing the wall 102’ corresponds to the model element 102 representing the corresponding wall. In case of a positive outcome 306a of the comparison, i. e., if a section of the point cloud is identified which corresponds to a model element, the mobile device 200, 200a stores 308 the information that the model element 102 was identified. More specifically, the mobile device 200, 200a, 200b adds a new entry to a list of identified elements stored on its memory 204b. The new entry comprises the unique element identifier of the identified model element 102, a time stamp to describe when the model element 102 was identified, and optionally its position relative to the boundaries of the point cloud or to other elements identified therein. If multiple model elements are identified, the process steps related to the positive outcome 306a of the comparison are repeated for each element identified. In embodiments wherein a wireless connection to a server system and/or to another mobile device 200, 200a, 200b via the communication interface 206 is available, the mobile device 200, 200a, 200b also sends the new entry using the wireless connection. After the comparison 306 is finished, the mobile device 200, 200a, 200b deletes 310 the point cloud as well as the images used for constructing the point cloud. Consequently, only a single point cloud and/or a few images are stored at the same time on the mobile device 200, 200a, 200b. This reduces the demands to the memory of the mobile device 200, 200a, 200b and consequently its costs. Moreover, personal data which may be potentially be contained in the images, such as an image of another person on the construction site, or a private item such as a cell phone of the person wearing the hard hat 200, 200a, 200b, are neither stored permanently nor sent by the mobile device 200, 200a, 200b. The mobile device 200, 200a, 200b is then ready for a next iteration 314, i. e. to acquire 304 a new point cloud, perform 306 a new comparison to the BIM 100, and send 312 the results if possible. At the end of the next iteration 314, the new point cloud is again deleted 310. In embodiments, wherein a permanent wireless connection to a server system and/or another mobile device 200, 200a, 200b via the communication interface 206 is not available for sending 312 the results of the comparison 306 during the iteration 314, the list of identified elements is provided 312 at a later point in time. In such embodiments, the sending 312 may take place after a large number of iterations, for example when the mobile device 200, 200a, 200b is connected to the docking station by the end of a workday. The method 300 for construction site monitoring thus uses a distributed network for the data analysis to eliminate process steps related to merging data sets, which may be computationally demanding. The results provided by the mobile devices 200, 200a, 200b, i. e. the lists of identified elements, contain small amounts of data in a form which may be processed quickly using known techniques. In particular, the processing may be much faster than the construction steps on the construction site 100’. The method may thus provide a continuous construction progress monitoring. The mobile devices 200, 200a, 200b of the distributed network use computer components which are available at moderate costs, for example as consumer products.

Fig. 5 shows a flow chart according to a second embodiment of a method 400 for construction site monitoring according to the present disclosure. The method is similar to the one described in the context of Fig. 4, and corresponding process steps are indicated with same reference numbers. In the embodiment of Fig. 5, the reliability of the comparison is further improved using a measured location provided by the localization unit 208 of the mobile unit 200. In the method 400 of Fig. 5, an initial reference point is provided 402. The initial reference point fully describes the initial position of the hard hat 200 and its initial orientation. More specifically, the initial reference point fully describes the initial position and the initial orientation of the scanner unit 202 in three-dimensional space and with respect to a static coordinate system of the construction site. For providing the initial reference point, the hard hat 200 is positioned in its docking station. The position of the docking station on the construction site and its orientation have beforehand been calibrated. The information about the calibrated initial position and initial orientation of the hard hat 200 in the docking station are then transferred to and stored on the hard hat 200 via the USB interface. This procedure is performed automatically when the hard hat 200 is connected to the docking station for charging. Typically, the worker positions the hard hat 200 in the docking station for charging by the end of a workday, the initial reference point is provided to the hard hat 200 by the docking station during the charging, and at the beginning of the next workday, the worker takes the hard hat 200 from the docking station and continues promoting the construction. A measured location is continuously generated 404 using the initial reference point and location data from the localization unit 208. For generating the measured location, the localization unit 208 provides location data in the form of a position and an orientation according to the inertial measurement unit. In a preferred embodiment, in addition to the measured location representing the current location of the electronic hard hat 200, a trajectory of the electronic hard hat 200 from the initial reference point to its current measured location is determined using the IMU and the initial reference point. The location data may further use complementary location data from a compass, a GPS position signal, and a position determined using the Bluetooth wireless transceiver, if a Bluetooth network is available. The generation 404 of the measured location is performed in iterations 406 at a rate which is similar to the rate of the iterations 314 of the point cloud acquisition 304. The method 400 of Fig. 5 comprises storing 302 a BIM model 100 and acquiring 304 a point cloud as similarly described in the context of the method of Fig. 4. According to two embodiments of the method 400 of Fig. 5, the measured location is used in two different ways for determining 410 an absolute position of the section of the point cloud corresponding to the model element 102 identified in the comparison 306. According to the first of the two embodiments, the measured location is used after a positive outcome 306a of the comparison, i. e. when a section of the point cloud corresponding to a model element 102 has been identified. In this case, the position of the section of the point cloud is referenced 408a to the static coordinate system of the construction site, and to the static coordinate system 108 of the BIM, respectively, using the measured location. This way, an absolute position of the section of the point cloud corresponding to the model element 102 is determined.

According to second, preferred embodiment, the measured location is used to reference 408b the point cloud after its acquisition 304 to the static coordinate system of the construction site, and to the static coordinate system 108 of the BIM, respectively. The absolute spatial information of the referenced point cloud is then compared 306 to the BIM 100, which comprises the model element locations, at a reduced computational cost. In addition, the absolute spatial information is used to check the assignment of the section of the point cloud to the model element 102 for consistency. After determining 410 the absolute position of the section of the point cloud corresponding to the model element 102, this absolute position is compared to the model element location of the model element 102 according to the BIM 100. The assignment is only considered consistent if the two essentially match. The flow diagram of Fig. 5 depicts a method 400 in which both the referencing 408b of the point cloud and the referencing 408a of the section of the point cloud which corresponds to the model element are performed for determining 410 the absolute position of the section of the point cloud corresponding to the model element 102. However, embodiments may comprise only one of the two referencing processes 408a, 408b for determining 410 the absolute position.

Fig 6 shows a flow chart of a method 416 for construction process monitoring according to an embodiment. The method is similar to the one described in the context of Fig. 5, and corresponding process steps are indicated by same reference numbers. In the embodiment illustrated in Fig. 6, the accuracy of the measured location is further improved by applying a correction 414 to the measured location. The correction 414 uses the deviation between the measured absolute position of a construction site element and its position according to the BIM 100. When a model element 102 is identified 306a after acquisition 304 of the point cloud, the absolute position of the section of the point cloud corresponding to the model element is determined 410. Although not shown, this may involve the referencing 408b of the point cloud or the referencing 408a of only the section of the point cloud corresponding to the model element to the generated 404 measured location. The determined 410 absolute position is then compared to the model element location according to the BIM 100 stored 302 on the mobile device 200, and a calculation 412 of the location deviation between the two is performed. A correction 414 of the measured location is then performed accounting for the calculated 412 location deviation. The correction 414 is carried out continuously in each iteration wherein a model element 102 is identified 306a. In this way, the accuracy of the measured location is significantly improved. If several model elements 102, 104, 106 of the BIM 100 are identified 306a in the comparison 306, the absolute position is determined 410, the location deviation is calculated 412for each of the identified model elements 102, 104, 106. The location deviations for the several model elements 102, 104, 106 are averaged, and the correction 414 is performed using the averaged location deviation.

In the state of the art (without the correction 414), the deviation between the measured location generated 404 by the localization unit and the actual location of the electronic hard hat 200 typically increases with time. This is related to the fact that the measured location provided by the localization unit uses relative location referencing, based primarily on data obtained with the IMU. The errors of the relative location referencing accumulate over time. The deviation may increase quickly and reach one or a few meters over the course of a workday. This accuracy still permits to determine the section of the BIM 100 relevant for the comparison 306 to the acquired 304 point cloud, reducing the computational cost significantly as compared to a comparison 306 between the acquired point cloud and the entire BIM 100. The accuracy may be improved using dedicated additional installations at the construction site that the localization unit interacts with to determine its location, such as radio-frequency identification (RFID) or Bluetooth senders and receivers. However, both the dedicated additional installations at the construction site and the additional equipment of the electronic hard hat 200 cause additional costs. In addition, maintaining the additional installations at the changing construction site may be challenging and costly. With the addition correction 414 according to the embodiment of Fig. 6, the measured location is corrected taking into account absolute positions. Error accumulation is avoided. Within a region of a few centimeters, the BIM 100 typically contains only one or a few model elements 102, 104, 106 which are compared to the point cloud in the comparison 306. Therefore, the method according to the embodiment of Fig. 6 has a minimized computational cost, and the comparison 306 can be performed on a low-performance processor 204a, which reduces the cost of the hardware components, increases battery lifetime of the mobile device 200, 200a, 200b, and is also beneficial for the miniaturization of the electronic components of the mobile device 200, 200a, 200b. A lightweight battery, such as a lithium battery, with a moderate energy storage capability, supplies the electric energy for operating the mobile device 200, 200a, 200b and is comprised therein. As a result of the distributed construction site monitoring according to any of the embodiments of Fig. 4, Fig. 5, or Fig. 6, a different list of identified elements is stored on each of the mobile units 200, 200a, 200b.

Fig. 7A and Fig. 7B illustrate computer systems for merging the different lists of identified elements of the individual mobile units 200, 200a, 200b and for generation of a consistent computer model of the construction site in its current state, also referred to as an as-built BIM. Fig. 7A illustrates an embodiment wherein a wireless connection 206’ between the mobile units 200, 200a, 200b is permanently available via their respective Bluetooth wireless transceivers. Via the permanent wireless connection, the mobile units 200, 200a, 200b exchange their respective lists of identified elements. As the communication interfaces 206 of the mobile devices 200, 200a, 200b use a low-power signal transmission, the wireless connection 206’ has a limited range, and repeaters and routers are provided at the construction site to establish the permanent wireless connection 206’. All lists of identified elements are also provided to a server system 500 using the same Bluetooth wireless connection 206’. The server system 500 comprises a tablet computer 502 located at the construction site and a workstation 506 remote from the construction site and connected to the tablet computer 502 via the internet 504 or a 4G or 5G wireless connection 504. The tablet computer 502 provides a visualization of the construction site progress based on the lists of identified elements. It is a mechanically rugged system suitable for operation under theharsh conditions at a construction site. The workstation 506 is equipped with a powerful processor and graphic card and sufficient memory for improved visualization of the as-built BIM and for re-optimization of the BIM 100 of the building to be constructed. For the same purposes, the workstation 506 comprises peripheral devices 508 for human input and output such as a monitor, a keyboard and a mouse. The computer system 500 according to the embodiment of Fig. 7A provides a maximum of flexibility with respect to distributing the tasks of merging the different lists of identified elements, constructing an as-built BIM using the lists, and re-optimizing the BIM of the building to be constructed according to the as-built BIM. Any of the tasks may be performed either by the mobile units 200, 200a, 200b, the tablet computer 502 at the construction site, or the remote workstation 508. When a re-optimization of the BIM is performed on the server system 500, the resulting re-optimized BIM is transferred to the mobile units 200, 200a, 200b using the wireless connection 206’ and replaces the BIM 100 in the subsequent construction site monitoring. The server system 500 of Fig. 7A comprises two computers, namely the tablet computer 502 and the workstation 508. More or less computers may be used according to the requirements of the specific construction site. For example, several workstations may be included to provide the as-built BIM to several entities involved in the construction process, such as a project manager, an architect, or corresponding entities of different contractors and subcontractors. On the other hand, if sufficient computer resources available at the construction site, the remote workstation 508 may be omitted and the as-built BIM may only be provided locally to omit transmission via the internet 504 and improve data protection.

Fig 7B shows a computer system without a permanent wireless connection between the mobile units 200, 200a, 200b. This embodiment relaxes requirements to the wireless network and also reduces the power consumption of the mobile units 200, 200a, 200b, thus enhancing their battery lifetime. According to the embodiment of Fig. 7B, each mobile unit 200, 200a, 200b transfers its list of identified elements individually to the server system 500 using the USB connector of its communication interface 206. Typically, this takes place automatically when a worker positions a hard hat 200 in its docking station for charging by the end of a workday. In this embodiment, the tasks of merging the lists of identified elements, constructing the as built BIM using the lists, and re-optimizing the BIM of the building to be constructed are all performed by the server system 500. After a re-optimizing the BIM, the re-optimized BIM is transferred from the server system 500 to the mobile units 200, 200a, 200b as soon as the connection 206’ is available after the reoptimization. Typically, the re-optimization is performed during the charging of the hard hat 200, and the re-optimized BIM is transferred to the hard hat 200even before the worker takes it from the docking station at the beginning of the next workday. Subsequent construction progress monitoring with the mobile unit 200, 200a, 200b uses the re-optimized BIM instead of the original BIM 100.

Claims

24 Patent claims

1. A system for bulding construction progress monitoring, said system comprising:

- and a server comprising: o a server processor and a server memory functionally coupled to the server processor, said server being connectable to the at least one mobile device, wherein the server is provided with a building information model of the building to be constructed and the model of the construction site on the server memory, characterized in that:

- the at least one mobile device is configured to execute at least the following operations: o receiving using the receiver and storing using the mobile memory at least a part of the building information model of the building to be constructed sent by the server, wherein the at least part of the building information model comprises a first plurality of model elements, each equipped with a descriptor, which comprises an ID of the element, which is automatically assigned to each element in the whole building information model, o acquiring using the scanner unit a spatial information of a construction site of the building to be constructed; o comparing, using the mobile processor, the spatial information and a model element of the first plurality to decide whether a section corresponding to the model element exists in the spatial information; and o if the section corresponding to the model element exists the at least one mobile device is configured to send using the sender at least a part of the descriptor of the model element to the server for updating the model of the construction site stored on the server,

- the server is configured to execute at least the following operations: o receiving at least part of the descriptor of the model element sent by the mobile device and storing it to the server memory; and o updating, using the server processor and the at least part of the descriptor of the model element, the model of the construction site, in order to track progress of the building contruction process. The system according to claim 1 , wherein the at least one mobile device is further configured to execute, if the section corresponding to the model element exists, the following:

- determining, using the mobile processor, a relative position of the section corresponding to the model element within the spatial information;

- optionally sending the relative position of the section corresponding to the model element along with the at least part of the descriptor. The system according to any claim from 1 to 2, wherein the building information model is related to a static coordinate system, wherein the mobile device further comprises a localization unit and wherein the device is further configured to execute the following:

- providing, using the localization unit, measured location for the spatial information relative to the static coordinate system;

- referencing, using the mobile processor and the measured location, the spatial information to the static coordinate system to obtain an absolute spatial information; and, if the section corresponding to the model element exists:

- determining, using the mobile processor and the absolute spatial information, an absolute position of the section corresponding to the model element within the static coordinate system; and

- optionally sending the absolute position of the section corresponding to the model element along with the at least part of the descriptor. The system according to claim 3, wherein the descriptor comprises a model element location, and wherein the mobile device is further configured to, if the section corresponding to the model element exists, execute the following:

- comparing, using the mobile processor, the model element location and the absolute position of the section corresponding to the model element; and optionally:

- sending a result of the comparison along with the descriptor, or

- sending the at least part of the descriptor only if the model element location and the absolute position of the section corresponding to the model element essentially match. The system according to any of the claims 3 to 4, wherein the mobile device is further configured to execute the following:

- calculating, if the model element location and the absolute position of the section corresponding to the model element essentially match, using the mobile processor, a location deviation between the model element location and the absolute position of the section corresponding to the model element; - storing the location deviation on the mobile memory and/ or correcting the measured location accounting for the location deviation to obtain a corrected measured location;

- redoing the referencing accounting for the location deviation or the corrected measured location; and

- optionally redoing the determining the absolute position of the section corresponding to the model element within the static coordinate system, in particular prior to the optionally sending the absolute position of the section corresponding to the model element along with the descriptor. The system according to any of the claims 3 to 5, wherein the mobile device is further configured to execute the following: performing, after they have been finished according to a first iteration, at least a second iteration of the process steps of acquiring the spatial information of the construction site, and comparing a model element of the first plurality and the spatial information to decide whether a section corresponding to the model element exists in the spatial information, thereafter performing the process steps of claims 2 and 3 again to determine a measured location for the spatial information of the second iteration and an absolute position of the section corresponding to the model element of the second iteration, correcting the measured location for the spatial information of the second iteration and/or the absolute position of the section corresponding to the model element of the second iteration accounting for the location deviation of the first iteration. The system according to any of the preceding claims, which is further configured to execute the following:

- generating an element time stamp associated with the section corresponding to the model element, and

- sending the element time stamp together with the at least part of the descriptor. The system according to any of the preceding claims, wherein a list is stored on the mobile memory, and wherein the device is further configured to execute storing, whenever a comparing finds that a section corresponding to a model element exists, at least one of the following in the list:

- at least a part of the descriptor of the model element;

- the relative position of the section corresponding to the model element,

- the absolute position of the section corresponding to the model element,

- the element time stamp, 27

- the result of comparing the model element location and the absolute position of the section corresponding to the model element,

- the location deviation between the model element location and the absolute position of the section corresponding to the model element; and

- the corrected measured location accounting for the location deviation. The system according to any of the preceding claims, wherein the mobile device is a wearable electronic device, in particular an electronic hard hat, or a device suitable for mounting on a mobile work equipment, on a construction machinery, or on a construction or inspection robot. A method for continuous construction progress monitoring using the system according to any of the preceding claims, wherein the method comprises at least the following steps: a) providing the server with a building information model of the building to be constructed and storing the model of the construction site on the server memory, b) sending the model of the construction site from the server to the at least one mobile device, wherein the at least part of the building information model comprises a first plurality of model elements, each equipped with a descriptor, c) storing information obtained in the previous step on the memory of the mobile device, d) acquiring using the scanner unit of the mobile device a spatial information of a construction site of the building to be constructed; e) comparing, using the mobile processor, the spatial information and a model element of the first plurality to decide whether a section corresponding to the model element exists in the spatial information; and f) if the section corresponding to the model element exists the at least one mobile device is configured to send using the sender at least a part of the descriptor of the model element to the server for updating the model of the construction site stored on the server, g) receiving at least part of the descriptor of the model element sent by the mobile device to the server and storing it to the server memory; and h) updating, using the server processor and the at least part of the descriptor of the model element, the model of the construction site, in order to track progress of the building contruction process. The method according to claim 11 , which further uses an additional mobile device comprising an additional mobile processor, an additional mobile memory and an additional scanner unit both functionally coupled to the additional mobile processor, an additional receiver and an additional sender both functionally coupled to the additional mobile memory; wherein the method further comprises: 28 i) sending at least a second part of the building information model from the server memory; j) receiving, using the additional receiver, the at least second part of the building information model comprising a second plurality of model elements, each with a descriptor; k) storing the at least second part of the building information model to the additional mobile memory; l) acquiring, using the additional scanner unit, an additional spatial information of the construction site; m) comparing, using the additional mobile processor, a model element of the second plurality and the additional spatial information to decide whether a section corresponding to the model element of the second plurality exists in the additional spatial information; and n) if the section corresponding to the model element of the second plurality exists, sending, using the additional sender, at least part of the descriptor of the model element of the second plurality for updating the model of the construction site; o) receiving the at least part of the descriptor of the model element of the second plurality at the at least one server and storing it to the server memory; and p) if the section corresponding to the model element of the first plurality exists, using the descriptor of the model element of the second plurality in addition to the server processor and the at least part of the descriptor of the model element in the updating the model of the construction site. A computer program adapted to instruct a computer system to execute the method according to any claim from 10 to 11.