Non-Invasive Data Collecting from 3D Laser Scanning of Objects Covered by the Historic Buildings Conservation Plan, for The Purpose of Their Restoration Joanna A. Pawłowicz, Elżbieta Szafranko Faculty of Geodesy, Geospatial and Civil Engineering, Institute of Building Engineering University of Warmia and Mazury in Olsztyn, Poland Abstract: Historic buildings are often characterised by an intricate structure, complexity of form or architectural details. In such case, no renovation work can be carried out without preparing relevant technical documentation. Old buildings often lack original documentation, which makes it necessary to reconstruct it through property condition survey. The article discusses the problems of development of such a survey for objects covered by the historic buildings conservation plan, on the basis of their measurements with a 3D laser scanner. Non-invasiveness of scanning is a great advantage of this solution which allows representing in the form of a dot cloud details difficult to document using classic methods. Keywords: 3D model, construction works, dot cloud, historic building, property condition survey, refurbishment and modernisation of a building, renovation. I. INTRODUCTION Revalorisation of historic buildings is a time-consuming and painstaking process. Such objects are often in a very bad technical condition, and their aesthetics and functionality is questionable. Correct course of the renovation process requires preparation of thorough documentation, e.g. current condition survey, opinion on the technical condition of the building or a project of restoring its utilitarian value and highlighting its features related to cultural heritage. Such renewal actions are related to the performance of restoration and adaptation works which, at a maximum preservation of historic values, will make it possible to adapt the building functionally to the users' expectations, and integrate it with its urban environment in spatial context. The above-mentioned solutions, complemented by economic and social actions aimed at the functional and utilitarian improvement of the building, are known under the common name of revitalisation. Restorers may make use of many methods to "recover" and "renovate" heritage objects, renewal being a popular method of restoration work. Their correct accomplishment is based, at the first stage, on the study of bibliography, archives and inventories, which allows reliable recovery of the documentation of the object. In the following steps, the direction of the protection and its scope are established; conservation guidelines and the program of works are developed, in order to improve functionality. In the last phase, the implementation project is prepared, along with obtaining necessary consents which guarantee that the building will meet the requirements of binding regulations. This article presents an innovative survey method which allows obtaining of data about constructions that may be used to recreate their documentation. The method may be especially valuable in compiling technical and architectonic documentation of historic objects. Available online @ www.ijntse.com 32
II. FIELD STUDIES 3D SCANNING 3D scanning is a state-of-the-art method with unlimited possibilities, based on laser technology. Its basic quality is the quickness of obtaining a large number of data in a very short time, which results in a huge advantage over existing measurement methods. Scanning can be used in works like engineering, surveying, inventory of complex buildings and objects (e.g. historic ones), as well as in structure deformation studies [1]. A 3D scanner is a device which analyses the measured building in real time and collects data regarding the shape, surface and texture of the studied object and its surroundings. Measurements carried out properly make it possible to process the data and create a fully digital, three-dimensional model of the object. The scanner is an instrument which, after being set on a levelled, stable tripod, collects the data turning around its own axis. The fundamental principle of its functioning is the measurement of the distance and angle between the device and the scanned object with a laser ray sent; the latter, after rebounding from the obstacle, returns to the instrument. These magnitudes allow visualising the surface of the studied object by creating a dot cloud, with specific coordinates X, Y, Z, oriented with respect to the local coordinate system of the device. The dot cloud, along with photographs used for texturizing the object, creates a realistic visualisation of the building [2]. Preparation and carrying out the measurements in the field entail the need of prior reconnaissance of the measured building and its surroundings. First of all, it is necessary to determine where the posts with the instrument should be situated and how to distribute the measurement dials which will be used to connect the scans from with all the positions of the instrument in one image at the data processing stage. The scanner should be set in such a manner that the laser beam can reach all the details of the studied object. Incorrect setting or insufficient number of posts of the device may lead to data lack, resulting in obtaining an incomplete 3D image of the object. It is therefore necessary to pay attention to an optimal distance between the instrument and the measured object. It is an important problem and resolving it allows obtaining high accuracy of the measurements and influences the reduction of the number of dead spots on the measured solid. It is connected with the fact that the scanner situated is too close to the building will result in too acute an angle of incidence of the laser beam, which will prevent the beam from reaching all details of the roof and will lead to the formation of unmeasured fragments, the so-called dead spots. The dead spots are spaces which cannot be measured from any of the posts. It is a common problem in measuring high or complexly structured objects situated on small or narrow plots where an appropriate distance of the instrument is not possible. They most frequently appear in places where one element of the building is covered by another fragment. One example of it may be a chimney blocking out the view of a part of the roof with a ridge, or corners of a building hidden behind a driveway parapet (Fig. 1). Unfortunately, it is also often impossible to bypass obstacles not belonging to the building, i.e. most frequently other buildings and structures, parked cars or plants surrounding the studied object. They prevent the laser beam from getting to the selected place from one or more scanner positions. Since the fragment in question will not be visible from any position of the instrument, the virtual model of the building will contain spots with lesser dot cloud saturation. This is seen as shadows, often taking the form of the obstacle which blocked out the view of the building, e.g. a tree (Fig. 2). Available online @ www.ijntse.com 33
Fig. 1. Dead spots formed during scanning of the object (marked with the white line) Fig. 2. Dot cloud representing the façade of a building with visible tree-shaped shadows Atmospheric conditions constitute an additional problem, making it difficult to take an accurate Available online @ www.ijntse.com 34
Joanna. A. Pawłowicz, Elżbieta Szafranko / International Journal of New Technologies in Science and Engineering photograph of the object, often appearing at the data collecting stage. Rainfalls or snowfalls, as well as fog, are particularly bothersome. Small droplets of water contained in the air are an obstacle for the laser which hits them, resulting in the beam rebound and split, causing many deformations in the dot cloud. Similar phenomenon can be observed during measurements in an atmosphere with high content of dust. Such kind of distortion is called "noise" and caused by extra points, not connected to the model; it must be removed during the processing. The greater the noise will be the less accurate model will be created. However, if a dot cloud dense enough is measured, light precipitation will not significantly affect the results. At the same time, it should be borne in mind that dirt or splashes on optical parts of the device may seriously distort them. Noise appears also in the case where a fragment of the laser spot falls on a ridge of the object during the measurement, which causes part of the signal to return to the receiver, while the other part rebounds from another object placed farther. It is the so-called signal echo which may cause significant difficulties in compiling the data [3]. III. COMPILING THE PROPERTY CONDITION SURVEY DOCUMENTATION The data obtained during the measurement form a dot cloud, processed with specialised computer software after downloading form the measuring device. After connecting all the posts in one model and cleaning it of unnecessary elements, it is possible to make quick building survey drawings. Quick projections and sections can also be created using the "Limit Box" function which generates a hexagon with cutting edges. They can cut the model of the building in any place, becoming a "slice", on the basis of which it is possible to develop vertical or horizontal sections of the building (Fig. 3). It is possible to define different dimensions on their basis: straight and diagonal ones, diameters, curve lengths, as well as any kind of angles etc. Fig. 3. Plan view of the building Scanned interiors of rooms may also be represented in the form of sections based on the contour of the Available online @ www.ijntse.com 35
dot cloud, cut by the reference plane. The dot cloud may be cut in several ways, using program features adequate for this purpose. This solution makes it possible to trace an exact contour of the elements in the projection. The type of option used in the software gives a possibility to make a section, a full view (fig. 4) or a contour view (fig. 5). Fig. 4. Full view of a building from above, in plan view The drawings created in this way contain many details which may be measured and their situation in respect of each other may be defined. This possibility is very useful in the case where we need to make a survey of a complex and intricate space with difficult access and where the survey cannot be carried out using traditional methods, as it happens e.g. in the case of a complex roof or a decorated façade of a building. Fig. 5. Contour view of a façade of a building The data obtained from measuring also give a possibility of preparing an axonometric of a building or Available online @ www.ijntse.com 36
a visualisation of an elevation. What can be used for this purpose is the dot cloud obtained in field measuring, making up a model of the object, immediately after completing the connection of the data from each position. The image may be represented as a "raw" dot cloud (Fig. 6) or a cloud with applied photographs (Fig. 7), giving an image of the colours and texture of the object [4]. Fig. 6. Three-dimensional model of a building "raw" dot cloud Fig. 7. Three-dimensional model of a building dot cloud with applied photographs Available online @ www.ijntse.com 37
IV. CONCLUSION Taking into account the permanent strive for modernisation and acceleration of design and construction work, the proposed method using 3D laser scanning in the development of historic building surveys is suitable, as it allows its easy application. In the construction process, it is often necessary to develop such documentation for the object whose documentation has been lost or is out of date, as it often happens in the case of historic objects. Documentation obtained in this innovative way can be safely used for conducting the building restoration process. Fig. 8. Damages and losses in the side elevation of the building Thanks to accurate, three-dimensional imaging of the object, it is possible to make the survey and describe damages and losses in its structure or in the elevation of the building (Fig. 8) and measure their size. On this basis, it is possible to assess the technical condition of the object, the conservation officer will be able to develop guidelines, the architect and the designer will prepare a new construction project, and the cost estimator will assess the implementation cost for the investment project [5]. At the stage of the preparation of the tender specification concerning construction works in the building, such documentation may be also made available for bidders. Usefulness of 3D laser scanning can for certain be confirmed in each of the questions considered. It is an unusual technology, with a countless number of potential applications, including the broad spectre of uses in construction which depend only on human imagination. Available online @ www.ijntse.com 38
REFERENCES [1] Bojarowski K., Dumalski A., Kamiński W., Mroczkowski K., Trystuła J., Ocena możliwości wykorzystania skanera laserowego ScanStation firmy Leica w badaniu deformacji obiektów budowlanych; Czasopismo Techniczne, Kraków, Wydawnictwo Politechniki Krakowskiej, 2008. [2] Dubik A., Zastosowanie laserów, Warszawa, Wydawnictwo Naukowo-Techniczne, 1991. [3] Pawłowicz J. A., 3D modelling of historic buildings using data from a laser scanner measurements; Journal of International Scientific Publications: Materials, Methods and Technologies Volume 8, p. 340-345, 2014. [4] Pawłowicz J.A., Szafranko E., Recording and analysis of anomalies appearing in structures of wooden construction objects using the 3D laser scanner, International Scientific Publication, Materials, Methods & Technologies, Volume 9/2015, p. 178-184, [5] Szafranko E., Pawłowicz J. A., Inventory of agricultural building objects based on data obtained from measurements by laser scanning, 14th ISC Engineering for Rural Development 20-22.05. 2015 Jelgava, Latvia, Proceedings p. 190-194, Joanna Agnieszka Pawłowicz: Dr Eng. surveying, urban planner, Assistant Professor at the Institute of Civil Engineering, Faculty of Geodesy, Geospatial and Civil Engineering, University of Warmia and Mazury in Olsztyn (Poland). Professionally interested in the use of modern technologies in construction. I perform inventories of architectural and construction of buildings and structures measurements using terrestrial laser scanning technology and analysis of historical buildings on the basis of point clouds obtained from the measurement object 3D laser scanner. Elżbieta Szafranko: Dr Eng. civil engineering, Assistant Professor at the Institute of Civil Engineering, Faculty of Geodesy, Geospatial and Civil Engineering, University of Warmia and Mazury in Olsztyn (Poland). Professionally interested in management, economic and planning in construction and civil engineering, inter alia, using the terrestrial laser scanning methods. Author of numerous publications about the preparation and execution of construction and road projects. Available online @ www.ijntse.com 39