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Digital Survey of Damages on the Façade of a Historical Building

Digital Survey of Damages on the Façade of a Historical Building Acta Sci. Pol. Architectura 20 (2) 2021, 41–50 content.sciendo.com/aspa ISSN 1644-0633 eISSN 2544-1760 DOI: 10.22630/ASPA.2021.20.2.13 ORIGINAL P APER Received: 14.01.2021 Accepted: 18.03.2021 DIGITAL SURVEY OF DAMAGES ON THE FAÇADE OF A HISTORICAL BUILDING Joanna A. Pawłowicz Faculty of Geoengineering, University of Warmia and Mazury in Olsztyn, Olsztyn, Poland ABSTRACT This study discusses the application of 3D terrestrial laser scanning (TLS) in the evaluation of the technical condition of a historical building – a brewery located in the town of Szczytno (Poland). The digital database was obtained entirely by means of a Leica ScanStation C10 laser scanner. The works involved obtaining and connecting the scanning data, followed by their application in determination of the extent of damages on a virtual model of the building. The study discusses the efficiency of a laser scanner in surveying damages to a historical building. The measurements were hampered by numerous factors, such as the location of measur- ing points, street traffic, by standers and adverse weather conditions. However, application of TLS method using an impulse scanner allows quick digitization of an entire object, what is of great importance when it comes to examining large buildings. It should be pointed out that this is one of the few methods which allow points located in poorly accessible places, e.g. on top of a roof or a tower, to be recorded from the ground level. A laser scanner is ideal for digital capturing of details of historical buildings. It is particularly useful in measuring damages or architectural details. Digital data so obtained can then be analysed using a computer in comfortable conditions. A disadvantage of the laser scanning is a large amount of accidental and undesired data, which requires a time-consuming filtration of a point cloud. Digitized data facilitates the research pro- cedure as it allows detailed measuring of complex objects in comfortable conditions. Key words: terrestrial laser scanning (TLS), point cloud, technical condition of a building, building redeco- ration, building information model (BIM) This technology is incredibly useful in situations where INTRODUCTION it is necessary to create a virtual image of the body Collecting data related to the technical condition of and the details of a building for which no technical a building usually requires long and arduous work. documentation exists. The measurements are taken by Measuring each element requires great perceptiveness means of touch or touchless scanners which use laser and diligence, and practically the entire research is and structural light. To this end, some of them use also carried out in field conditions. Laser scanning facili- magnetic resonance. The result of the research is the tates this process. An instrument capable of collecting so-called point cloud, representing the surface and the digital data allows taking measurements without hav- geometry of the scanned objects. ing to go into details. The rest of the analyses, after Terrestrial laser scanning (TLS) is a contactless downloading the data, can be carried out while sitting method of imaging the surface of a researched object in front of the computer. A laser scanner is a starting by means of electromagnetic radiation emitted and re- point when obtaining digital data related to an object. ceived by a scanner. It is a static measurement consist- Joanna A. Pawłowicz https://orcid.org/0000-0002-1334-5361 jopaw@uwm.edu.pl © Copyright by Wydawnictwo SGGW Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 ing in measuring the polar coordinates: the distance ever, the current technology allows the use of terres- between a point and the device, and the direction of trial laser scanners which reduce the time needed to the laser beam. Based on this data, the X, Y, Z coordi- take the measurements, offer a greater accuracy and nates of the point are determined in a local coordinate the possibility of scanning from large distances. Both system of the measuring instrument. An additional co- solutions ensure contactless and non-invasive exami- ordinate is I, which determines the intensity of reflec- nation (Bernat et al., 2016). tion of the laser beam from the object (Wehr & Lohr, Digital surveying of buildings allows to evaluate 1999; Pawłowicz, 2017). The user decides about the their technical condition and appearance using a com- density of the measurements, which are taken by rotat- puter. In addition, this technology allows to determine ing the scanner around its own axis by a pre-defined the scope of conservation or modernisation works. How- horizontal and vertical angle. An advantage of the laser ever, its main advantage is that it enables recreation of scanning over the traditional methods is that one can individual elements which have been damaged. In con- obtain a large amount of data in a form of a point cloud servation of historical buildings, thorough examination within a few seconds. In aim to interpret small details of all architectural details is very important for their fu- more easily, a texture in a form of pictures taken by ture recreation (Van Genechten & Schueremans, 2009; the scanner camera can be superimposed on the point Pawłowicz, Bilko, Sawczyński & Szafranko, 2017). cloud. The points are assigned colours in the RGB The information obtained this way is also used to spatial colour model, which correspond with those in analyse the condition of the structure of a building, the pictures. The quality of the data obtained from the e.g. the verticality or bend ratio of its individual ele- laser beam is influenced by the following factors: ab- ments (Ćmielewski, 2011). Based on the recorded in- sorption of impulses by the atmosphere, reflection and tensity of the laser beam reflection, the level of wear dispersion from the surface of the researched object of the material from which a building was made is and the angle of incidence of the laser beam (Kaspar, examined. This way, it is also possible to detect e.g. Pospisil, Stroner, Kremen & Tejkal, 2004; Franceschi damp spots (Janowski, Nagrodzka-Godycka, Szulwic et al., 2009). In the case of dark surfaces, laser beam & Ziolkowski, 2016). absorption is greater, hence the reflected signal is weaker. In the laser scanning this means that the pre- MATERIAL AND METHODS cision of determining the location of a given point is lower. Bright surfaces, characterised by a greater re- Researched object – a Castle Brewery flection intensity, disperse more light, as a result of The object subjected to scanning is located in Szczytno which the precision of measuring the distances is near Olsztyn (Poland). Built in 1898, it is called the greater. A disadvantage of such materials is that with Castle Brewery (German: Schlossbrauerei Ortelsburg). too high share of reflection, the laser beam will reflect It derives its name from its shape resembling a castle. from a surface as if from a mirror and will approach The research was carried out in the oldest part of an undesired element or disperse in the space. This the neo-gothic complex (Fig. 1). In 1996, this part of may generate noise having a negative influence on the the building was entered into the register of historical quality of measurements (Zaczek-Peplinska, Góra & buildings of the Warmińsko-Mazurskie Voivodeship. Grzyb, 2015; Wujanz et al., 2018). Although the building’s architecture is strictly in- The technical condition of a historical building is dustrial, its red brick façades feature cornices, finely evaluated based on its survey carried out by means crafted arched window lintels and jambs. The build- of the traditional methods using the common tools: ing owes its charm also to the corner turrets decorated tapes, distance meter, crack meter etc., along with the with spikes. Figure 2 presents the effect of laser scan- close-range photogrammetry, where good lighting is ning of the said building in the form of a point cloud in required, or building a scaffolding to ensure accurate the upper part thereof, featuring ornaments and turrets results in the case of high-rise structures. These solu- (Fig. 2). The building is in a very bad state of repair and tions were time-consuming and inconvenient. How- requires renovation. Its façades are dirty and have a lot 42 architectura.actapol.net Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 Fig. 1. Laser scanner seen against the oldest part of the brewery – a view on the southern façade on the court side Fig. 2. A point cloud showing the roof featuring decorative turrets. In the foreground there is a cornice in the form of a parapet of holes and cracks. The same concerns the wooden The instrument was also used to make a series of pic- window and door frames, as well as the metal work. tures by means of a built-in digital camera. After super- imposing them on the point cloud in post-processing Measurements it was possible to recreate the natural texture and the Measuring the façade of the building lasted a few days. color of the object. The purpose of the measurement First, sketches of the building were prepared, along with was to collect digital data about the object and dam- its technical documentation. Due to the large size of the ages on it in the form of a point cloud (Fig. 2). building and its rich ornaments, a decision was made to apply the 3D laser scanning technology. Twenty- Data processing -eight scanning stations were prepared, both inside and The point cloud resulting from scanning contains more outside the brewery compound. The scanning stations than just information about the researched object; it were set up with particular attention being given to the also includes data generally referred to as noise. It re- architectural details and the visually apparent damages sults from the reflection of a laser beam from undesired to the façade. The scanner was placed as close to the and accidental objects (such as trees or bystanders). object as possible, with the laser beam being projected Another type of undesired data are points resulting onto it perpendicularly. The measurements were taken from incorrect or multiple reflection of a light beam by means of a 3D Leica ScanStation C10 laser scanner. (e.g. from glass surfaces). Therefore, a point cloud architectura.actapol.net 43 Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 needed filtrating after being entered into the computer. Example 1: Cracks in the walls This way it was cleared of any undesired elements and A crack extending from the ground level upwards was the damages were identified. Over 60 damages to the discovered on the eastern wall of the building (Fig. 3a). façade of the building were discovered, affecting the The crack was recorded during scanning. The scanner technical condition of the building. was placed 161 cm above the ground, 350 cm from the wall. The laser beam was projected at a 22-degree an- gle above the scanner lens axis and a 25-degree angle RESULTS beneath it (Fig. 4). The crack can be clearly seen in the Analysis of the damages to the façade point cloud with a superimposed texture. The image Three representative examples of structural and surface of the crack can be easily measured in the point cloud defects were selected for the purposes of this study. (Fig. 3b). The crack is 300 cm long. It is 3 cm wide at its They include different damages to the external walls widest, and less than 1 cm wide at its narrowest point. of the building, recorded by means of a laser scanner. The parameters of the crack are presented in the table. Fig. 3b. A portion of the crack mapped to a point cloud. Fig. 3a. Digital image of a The measurements are portion of the crack presented in the table Fig. 4. Example 1: a schematic view of the measure- ments of a crack on the eastern wall of the brewery (besides angles, measurements in centimeters) 44 architectura.actapol.net Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 Example 2: Crumbling of the construction material As the angle of the laser beam projection increases, Numerous gaps were discovered in the upper portion the possibility to measure the depth of gaps decreases. of the western wall of the building. They are irregular To prevent this, the scanner was placed as far as pos- in shape and result from crumbling or intentional re- sible from the scanned object in order to reduce the la- moval of bricks (Fig. 5). ser beam angle. Eventually the instrument was placed It was not possible to place the scanner at the level 630 cm away from the building, whereas the height of of the gaps during taking the measurements, which the target axis of the scanner was 161 cm. The meas- would have facilitated measuring their depth. urements taken based on the point cloud helped iden- Therefore, the instrument was placed perpendicu- tify the area of the gaps and their location (the table). lar to the wall, with the laser beam being projected at The damages are located at the height ranging from an angle ranging from 39 to 47° above the lens axis. 664 to 818 cm (Fig. 6). Fig. 5. The western façade with visible gaps Fig. 6. Example 2: a schematic view of the measurements of the gaps on the western wall of the brewery (besides angles, measurements in centimeters) architectura.actapol.net 45 Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 As the laser beam is projected onto a gap at sharp angle, it reaches only the upper portions thereof. Consequently, it is not possible to arrive at a reliable measurement of the depth of these damages. It is worth noting that the smaller a gap, the more limited the laser beam range. This way the so-called blind spot is formed in a point cloud. Figure 7 shows that as the section of a gap increases, so does the depth of its penetration by a laser beam. The other measurements, such as the height and the width of a gap were easily measured in the point cloud (Fig. 8a). To better explain the issue related to measuring the depth of the gaps resulting from the Fig. 7. Example 2: a schematic view of the measurements large angle of the laser beam projection, a scan im- of the gaps on the western wall of the brewery (all age has been cut out and shown from the side op- measurements in centimeters) posite in relation to the measurements taken (from inside the building) (Fig. 8b). The table shows the measured. It is due the fact that the laser beam failed results of measuring the depth of the gaps based on a point cloud. However, it should be pointed out that to reach the rear edge of the gap (from the inner side these values are false as only the apparent depth was of the wall). Fig. 8a. A point cloud showing gaps in the façade resulting Fig. 8b. A section in the point cloud through the plane of from the crumbling of the building material. Tak- the scanned wall. Indicative depth of a gap in an ing measurements of the gaps (the table ) inverted view (the table) 46 architectura.actapol.net Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 Example 3: Damages caused by water and wind the pipes and gutters and to wash out the bricks and The southern façade seen from the court of the brew- the mortar joints. The damaged surface is clearly ery compound. Numerous damages were observed visible on the point cloud (Fig. 9b). Based on the here, caused mainly by water and wind. One of the scan, its area was estimated to cover ca. 90 cm . The analysed elements was a pillar between windows, damage starts at the height of 355 cm and ends at featuring water-washed bricks and mortar joints 455 cm (the table). The laser beam opening angle (Fig. 9a). This condition of the pillar results prob- ranges between 18 and 27° (Fig. 10) and was not of ably from a leaky system for removing rainwater great importance for measuring the damaged area in from the roof, causing the rainwater to flow out of the point cloud. Fig. 9a. Digital image of the washed-out bricks and mortar Fig. 9b. Washed-out bricks and mortar joint in the point joints cloud. The measurements are presented in the table Fig. 10. Example 3: a diagram of measuring the dam- ages on the southern wall of the building (be- sides angles, measurements in centimeters) architectura.actapol.net 47 Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 Table. List of all parameters of the damages presented in the study Example 3 Example 1 Example 2 Parameter Washed-out Crack Missing bricks material Gap 1: 29 Height [cm] 300 Gap 2: 38 130 Gap 3: 27 Gap 1: 43 Width [cm] 1–3 Gap 2: 56 70 Gap 3: 29 Gap 1: 28 Estimated depth [cm] – Gap 2: 43 – Gap 3: 33 Gap 1: 1247 Gap area [cm]23 Gap 2: 2128 9 100 Gap 3: 783 Distance between the scanner and the analysed damage [cm] 350 631 550 Height at which the damage is located [cm] 0–300 664–818 335–435 Angle between the laser beam and the analysed surface [°] from –25 to +22 from +39 to +47 from +18 to +27 Instrument height [cm] 161 161 161 Unreliable depth given as an example of actions performed on a point cloud. Evaluation of the measuring method difficult in this case, especially with regard to damages Over 60 damages on the façade of the brewery build- situated at a height. It would have also required using ing were identified during the survey, mostly corro- ladders or scaffoldings, which would have been con- sion and cavities resulting from destruction and lack of nected with a threat of a fall. In addition, using a scaf- repairs. In addition, numerous cracks in the walls were folding would have required attaching it to the build- discovered, possibly due to the instability of the soil, ing, which might have caused additional damages on but most likely due to the intensive vehicle traffic on it. This is always a significant issue, especially where the nearby regional road. a historical building is concerned. Moreover, some of the bricks are corroded and the Therefore, the survey was conducted using a 3D mortar joints are washed out. These damages do not laser scanner, which allows collecting the required form any regular pattern. Some of them are small and data in a non-invasive way, without posing any risk invisible at first glance, but some cover an area of up to the operator. However, a scanner is not an ideal de- to a few square meters. The table contains a list of pa- vice. A measuring station should be planned such as to rameters obtained by means of measuring selected ele- ensure that the laser beam does not hit an object at a ments in the point cloud. too big angle. Elements situated at a height should be The study presents three examples representing all measured from a bigger distance. This helps decrease of the analyses performed on the object. A significant the beam angle and allows deeper penetration of such difficulty in identifying and recording damages on an element. Placing a scanner too close to an object and object is inaccessibility of its individual elements. Tak- thus using too big angle of the laser results in the light ing measurements with use of traditional methods, e.g. beam failing to reach the details which are situated by means of tapes and gap gauges, would have been high above the ground or are concave. The result- 48 architectura.actapol.net Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 ing point cloud is then incomplete (blind spots). It is REFERENCES therefore confirmed that the most efficient scanning Bernat, M., Byzdra, A., Chmielecki, M., Laskowski, P., occurs when the scanner is positioned as close as pos- Orzechowski, J., Rzepa, S., Szulwic, J. & Ziółkowski P. sible to the perpendicularity relative to the plane being (2016). Zastosowanie naziemnego skaningu laserowe- scanned. During the point cloud analysis, it was also go i przetwarzanie danych: inwentaryzacja i inspekcja noted that the intensity of the laser beam reflection is obiektów budowlanych. Przegląd technologii i przykła- weaker when scanning a red brick surface, compared dy zastosowań. Gdańsk: Wydawnictwo Polskiego Inter- to other elements. However, this was not an obstacle netowego Informatora Geodezyjnego. to a thorough examination of the building. The data Ćmielewski, B. (2011). Identification deformation areas obtained in the form of a point cloud provides a lot of of slops using terrestrial laser scanner-preliminary re- search. In Proceedings of the 13th Professional Confer- information about the geometry and structure of the ence of Postgraduate Students (Juniorstav 2011). Brno: object, as well as about it technical condition. A cloud Akademické nakladatelství CERM. allows to observe and measure the damages and pre- Franceschi, M., Teza, G., Preto, N., Pesci, A., Galgaro, A. cisely determine their location and range. Calculation & Girardi, S. (2009). Discrimination between marls of their size forms a basis for planning and valuation and limestone using intensity data from terrestrial laser of repair works. scanner. ISPRS Journal of Photogrammetry and Re- mote Sensing, 64 (6), 522–528. https://doi.org/10.1016/ SUMMARY AND CONCLUSIONS j.isprsjprs.2009.03.003 Janowski, A., Nagrodzka-Godycka, K., Szulwic, J. & Ziol- Laser scanning allowed to create a digital database kowski, P. (2016). Remote sensing and photogram- metry techniques in diagnostics of concrete structures. related to the Castle Brewery with respect to its geom- Computers and Concrete, 18 (3), 405–420. https://doi. etry, structure and architectural detail. The resulting org/10.12989/cac.2016.18.3.405 point cloud enabled to survey the object and measure Kaspar, M., Pospisil, J., Stroner, M., Kremen, T. & Tejkal, the extent of the damages to it. Thanks to scanning, it M. (2004). Laser Scanning in civil engineering and land is possible to apply reverse engineering and model- surveying. Hradec Králové: Vega. ling later on. A point cloud is often a basis for creating Pawłowicz, J. A. (2017). Importance of Laser Scanning and modifying a digital model of a building. Such a Resolution in the Process of Recreating the Architectural virtual building can be supplemented with information Details of Historical Buildings. IOP Conference Series: about the structure, systems, materials used or recom- Materials Science and Engineering, 245 (5), 052038. mendations for maintenance and fire protection. Such https://doi.org/10.1088/1757-899X/245/5/052038 Pawłowicz, J. A., Bilko, P., Sawczyński, S. & Szafranko, E. information serves as a basis for a preparing a building (2017). Diagnostic of Geometry Distortion of a Wooden permit design using the building information model Structure Based on a Point Cloud. In 2017 Baltic Geo- (BIM) technology. A model prepared this way will detic Congress (BGC Geomatics) (pp. 163–168). IEEE. facilitate planning a renovation of a building, adapt- https://doi.org/10.1109/BGC.Geomatics.2017.55 ing it to the present requirements related to facilities Szafranko, E. (2014). Ways to determine criteria in multi- for the disabled, safety or construction standards. It criteria methods applied to assessment of variants of also facilitates adhering to work schedules and cost a planned building investment. Czasopismo Techniczne. estimates (Szafranko, 2014) and helps to foresee colli- Budownictwo, 2-B (6), 41–48. https://doi.org/10.4467/ sions with respect to discipline-specific or avoid addi- 2353737XCT.14.110.2560 tional costs of alterations. Finally, after the completion Van Genechten, B. & Schueremans, L. (2009) Laserscan- ning for heritage documentation. Wiadomości Konser- of construction work, it enables easy management of watorskie, 26, 727–737. a building and its operation. Point clouds are increas- Wehr, A. & Lohr, U. (1999). Airborne laser scanning – an in- ingly used to create digital models of existing facilities troduction and overview. ISPRS Journal of Photogram- in the BIM technology. architectura.actapol.net 49 Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 metry and Remote Sensing, 54 (2–3), 68–82. https://doi. Zaczek-Peplinska, J., Góra, A. & Grzyb, M. (2015). Analiza org/10.1016/S0924-2716(99)00011-8 statystyczna wartości Intensity (TLS) zarejestrowanych Wujanz, D., Burger, M., Tschirschwitz, F., Nietzschmann, na powierzchni konstrukcji betonowej. In M. Kwaśniak T., Neitzel, F. & Kersten, T. (2018). Determination of (Ed.), Techniki inwentaryzacji i monitoringu obiektów Intensity-Based Stochastic Models for Terrestrial Laser inżynierskich (pp. 90–105). Warszawa, Wydział Geode- Scanners Utilising 3D-Point Clouds. Sensors, 18 (7), zji i Kartografii Politechniki Warszawskiej. 2187. https://doi.org/10.3390/s18072187 CYFROWA INWENTARYZACJA USZKODZEŃ ELEWACJI BUDYNKU ZABYTKOWEGO STRESZCZENIE W pracy przedstawiono zastosowanie trójwymiarowego naziemnego skaningu laserowego (TLS) w ocenie stanu technicznego budynku zabytkowego na przykładzie browaru zlokalizowanego w Szczytnie (Polska). Wszystkie prace związane z uzyskaniem cyfrowej bazy danych wykonywano skanerem laserowym Leica ScanStation C10. Zakres prac obejmował pozyskanie i połącznie danych ze skaningu, a następnie określenie na ich podstawie skali uszkodzeń w wirtualnym obrazie budowli. W artykule omówiono skuteczność wy- korzystania skanera laserowego przy inwentaryzacji uszkodzeń obiektu zabytkowego. Podczas pomiarów napotkano na liczne ograniczenia, takie jak: trudne usytuowanie stanowisk, ruch na ulicach, ingerencja osób postronnych i niesprzyjające warunki atmosferyczne. Zastosowanie metody TLS wykorzystującej skaner im- pulsowy pozwala jednak na szybkie zdigitalizowanie całego obiektu, co przy inwentaryzacji dużych budyn- ków jest bardzo ważne. Warto dodać, że metoda ta jest jedną z nielicznych, która umożliwia inwentaryzację punktów trudno dostępnych, na przykład połaci dachowych czy wież, z poziomu terenu. Skaner laserowy doskonale nadaje się do cyfrowej inwentaryzacji obiektów zabytkowych. Szczególnie świetnie sprawdza się przy pomiarach uszkodzeń czy detali architektonicznych. Cyfrowe dane zebrane w terenie mogą być anali- zowane przed komputerem w komfortowych warunkach. Niewątpliwą wadą skaningu laserowego jest wystę- powanie dużej ilości danych przypadkowych i niepożądanych. Wiąże się to z wykonaniem pracochłonnej fil- tracji chmury punktów. Zdigitalizowane dane ułatwiają procedurę badawczą, ponieważ umożliwiają pomiary skomplikowanych obiektów przy zachowaniu maksymalnej szczegółowości i w kameralnych warunkach. Słowa kluczowe: naziemny skaning laserowy (TLS), chmura punktów, stan techniczny budynku, remont budynku, building information model (BIM) 50 architectura.actapol.net http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Acta Scientiarum Polonorum Architectura de Gruyter

Digital Survey of Damages on the Façade of a Historical Building

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Acta Sci. Pol. Architectura 20 (2) 2021, 41–50 content.sciendo.com/aspa ISSN 1644-0633 eISSN 2544-1760 DOI: 10.22630/ASPA.2021.20.2.13 ORIGINAL P APER Received: 14.01.2021 Accepted: 18.03.2021 DIGITAL SURVEY OF DAMAGES ON THE FAÇADE OF A HISTORICAL BUILDING Joanna A. Pawłowicz Faculty of Geoengineering, University of Warmia and Mazury in Olsztyn, Olsztyn, Poland ABSTRACT This study discusses the application of 3D terrestrial laser scanning (TLS) in the evaluation of the technical condition of a historical building – a brewery located in the town of Szczytno (Poland). The digital database was obtained entirely by means of a Leica ScanStation C10 laser scanner. The works involved obtaining and connecting the scanning data, followed by their application in determination of the extent of damages on a virtual model of the building. The study discusses the efficiency of a laser scanner in surveying damages to a historical building. The measurements were hampered by numerous factors, such as the location of measur- ing points, street traffic, by standers and adverse weather conditions. However, application of TLS method using an impulse scanner allows quick digitization of an entire object, what is of great importance when it comes to examining large buildings. It should be pointed out that this is one of the few methods which allow points located in poorly accessible places, e.g. on top of a roof or a tower, to be recorded from the ground level. A laser scanner is ideal for digital capturing of details of historical buildings. It is particularly useful in measuring damages or architectural details. Digital data so obtained can then be analysed using a computer in comfortable conditions. A disadvantage of the laser scanning is a large amount of accidental and undesired data, which requires a time-consuming filtration of a point cloud. Digitized data facilitates the research pro- cedure as it allows detailed measuring of complex objects in comfortable conditions. Key words: terrestrial laser scanning (TLS), point cloud, technical condition of a building, building redeco- ration, building information model (BIM) This technology is incredibly useful in situations where INTRODUCTION it is necessary to create a virtual image of the body Collecting data related to the technical condition of and the details of a building for which no technical a building usually requires long and arduous work. documentation exists. The measurements are taken by Measuring each element requires great perceptiveness means of touch or touchless scanners which use laser and diligence, and practically the entire research is and structural light. To this end, some of them use also carried out in field conditions. Laser scanning facili- magnetic resonance. The result of the research is the tates this process. An instrument capable of collecting so-called point cloud, representing the surface and the digital data allows taking measurements without hav- geometry of the scanned objects. ing to go into details. The rest of the analyses, after Terrestrial laser scanning (TLS) is a contactless downloading the data, can be carried out while sitting method of imaging the surface of a researched object in front of the computer. A laser scanner is a starting by means of electromagnetic radiation emitted and re- point when obtaining digital data related to an object. ceived by a scanner. It is a static measurement consist- Joanna A. Pawłowicz https://orcid.org/0000-0002-1334-5361 jopaw@uwm.edu.pl © Copyright by Wydawnictwo SGGW Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 ing in measuring the polar coordinates: the distance ever, the current technology allows the use of terres- between a point and the device, and the direction of trial laser scanners which reduce the time needed to the laser beam. Based on this data, the X, Y, Z coordi- take the measurements, offer a greater accuracy and nates of the point are determined in a local coordinate the possibility of scanning from large distances. Both system of the measuring instrument. An additional co- solutions ensure contactless and non-invasive exami- ordinate is I, which determines the intensity of reflec- nation (Bernat et al., 2016). tion of the laser beam from the object (Wehr & Lohr, Digital surveying of buildings allows to evaluate 1999; Pawłowicz, 2017). The user decides about the their technical condition and appearance using a com- density of the measurements, which are taken by rotat- puter. In addition, this technology allows to determine ing the scanner around its own axis by a pre-defined the scope of conservation or modernisation works. How- horizontal and vertical angle. An advantage of the laser ever, its main advantage is that it enables recreation of scanning over the traditional methods is that one can individual elements which have been damaged. In con- obtain a large amount of data in a form of a point cloud servation of historical buildings, thorough examination within a few seconds. In aim to interpret small details of all architectural details is very important for their fu- more easily, a texture in a form of pictures taken by ture recreation (Van Genechten & Schueremans, 2009; the scanner camera can be superimposed on the point Pawłowicz, Bilko, Sawczyński & Szafranko, 2017). cloud. The points are assigned colours in the RGB The information obtained this way is also used to spatial colour model, which correspond with those in analyse the condition of the structure of a building, the pictures. The quality of the data obtained from the e.g. the verticality or bend ratio of its individual ele- laser beam is influenced by the following factors: ab- ments (Ćmielewski, 2011). Based on the recorded in- sorption of impulses by the atmosphere, reflection and tensity of the laser beam reflection, the level of wear dispersion from the surface of the researched object of the material from which a building was made is and the angle of incidence of the laser beam (Kaspar, examined. This way, it is also possible to detect e.g. Pospisil, Stroner, Kremen & Tejkal, 2004; Franceschi damp spots (Janowski, Nagrodzka-Godycka, Szulwic et al., 2009). In the case of dark surfaces, laser beam & Ziolkowski, 2016). absorption is greater, hence the reflected signal is weaker. In the laser scanning this means that the pre- MATERIAL AND METHODS cision of determining the location of a given point is lower. Bright surfaces, characterised by a greater re- Researched object – a Castle Brewery flection intensity, disperse more light, as a result of The object subjected to scanning is located in Szczytno which the precision of measuring the distances is near Olsztyn (Poland). Built in 1898, it is called the greater. A disadvantage of such materials is that with Castle Brewery (German: Schlossbrauerei Ortelsburg). too high share of reflection, the laser beam will reflect It derives its name from its shape resembling a castle. from a surface as if from a mirror and will approach The research was carried out in the oldest part of an undesired element or disperse in the space. This the neo-gothic complex (Fig. 1). In 1996, this part of may generate noise having a negative influence on the the building was entered into the register of historical quality of measurements (Zaczek-Peplinska, Góra & buildings of the Warmińsko-Mazurskie Voivodeship. Grzyb, 2015; Wujanz et al., 2018). Although the building’s architecture is strictly in- The technical condition of a historical building is dustrial, its red brick façades feature cornices, finely evaluated based on its survey carried out by means crafted arched window lintels and jambs. The build- of the traditional methods using the common tools: ing owes its charm also to the corner turrets decorated tapes, distance meter, crack meter etc., along with the with spikes. Figure 2 presents the effect of laser scan- close-range photogrammetry, where good lighting is ning of the said building in the form of a point cloud in required, or building a scaffolding to ensure accurate the upper part thereof, featuring ornaments and turrets results in the case of high-rise structures. These solu- (Fig. 2). The building is in a very bad state of repair and tions were time-consuming and inconvenient. How- requires renovation. Its façades are dirty and have a lot 42 architectura.actapol.net Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 Fig. 1. Laser scanner seen against the oldest part of the brewery – a view on the southern façade on the court side Fig. 2. A point cloud showing the roof featuring decorative turrets. In the foreground there is a cornice in the form of a parapet of holes and cracks. The same concerns the wooden The instrument was also used to make a series of pic- window and door frames, as well as the metal work. tures by means of a built-in digital camera. After super- imposing them on the point cloud in post-processing Measurements it was possible to recreate the natural texture and the Measuring the façade of the building lasted a few days. color of the object. The purpose of the measurement First, sketches of the building were prepared, along with was to collect digital data about the object and dam- its technical documentation. Due to the large size of the ages on it in the form of a point cloud (Fig. 2). building and its rich ornaments, a decision was made to apply the 3D laser scanning technology. Twenty- Data processing -eight scanning stations were prepared, both inside and The point cloud resulting from scanning contains more outside the brewery compound. The scanning stations than just information about the researched object; it were set up with particular attention being given to the also includes data generally referred to as noise. It re- architectural details and the visually apparent damages sults from the reflection of a laser beam from undesired to the façade. The scanner was placed as close to the and accidental objects (such as trees or bystanders). object as possible, with the laser beam being projected Another type of undesired data are points resulting onto it perpendicularly. The measurements were taken from incorrect or multiple reflection of a light beam by means of a 3D Leica ScanStation C10 laser scanner. (e.g. from glass surfaces). Therefore, a point cloud architectura.actapol.net 43 Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 needed filtrating after being entered into the computer. Example 1: Cracks in the walls This way it was cleared of any undesired elements and A crack extending from the ground level upwards was the damages were identified. Over 60 damages to the discovered on the eastern wall of the building (Fig. 3a). façade of the building were discovered, affecting the The crack was recorded during scanning. The scanner technical condition of the building. was placed 161 cm above the ground, 350 cm from the wall. The laser beam was projected at a 22-degree an- gle above the scanner lens axis and a 25-degree angle RESULTS beneath it (Fig. 4). The crack can be clearly seen in the Analysis of the damages to the façade point cloud with a superimposed texture. The image Three representative examples of structural and surface of the crack can be easily measured in the point cloud defects were selected for the purposes of this study. (Fig. 3b). The crack is 300 cm long. It is 3 cm wide at its They include different damages to the external walls widest, and less than 1 cm wide at its narrowest point. of the building, recorded by means of a laser scanner. The parameters of the crack are presented in the table. Fig. 3b. A portion of the crack mapped to a point cloud. Fig. 3a. Digital image of a The measurements are portion of the crack presented in the table Fig. 4. Example 1: a schematic view of the measure- ments of a crack on the eastern wall of the brewery (besides angles, measurements in centimeters) 44 architectura.actapol.net Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 Example 2: Crumbling of the construction material As the angle of the laser beam projection increases, Numerous gaps were discovered in the upper portion the possibility to measure the depth of gaps decreases. of the western wall of the building. They are irregular To prevent this, the scanner was placed as far as pos- in shape and result from crumbling or intentional re- sible from the scanned object in order to reduce the la- moval of bricks (Fig. 5). ser beam angle. Eventually the instrument was placed It was not possible to place the scanner at the level 630 cm away from the building, whereas the height of of the gaps during taking the measurements, which the target axis of the scanner was 161 cm. The meas- would have facilitated measuring their depth. urements taken based on the point cloud helped iden- Therefore, the instrument was placed perpendicu- tify the area of the gaps and their location (the table). lar to the wall, with the laser beam being projected at The damages are located at the height ranging from an angle ranging from 39 to 47° above the lens axis. 664 to 818 cm (Fig. 6). Fig. 5. The western façade with visible gaps Fig. 6. Example 2: a schematic view of the measurements of the gaps on the western wall of the brewery (besides angles, measurements in centimeters) architectura.actapol.net 45 Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 As the laser beam is projected onto a gap at sharp angle, it reaches only the upper portions thereof. Consequently, it is not possible to arrive at a reliable measurement of the depth of these damages. It is worth noting that the smaller a gap, the more limited the laser beam range. This way the so-called blind spot is formed in a point cloud. Figure 7 shows that as the section of a gap increases, so does the depth of its penetration by a laser beam. The other measurements, such as the height and the width of a gap were easily measured in the point cloud (Fig. 8a). To better explain the issue related to measuring the depth of the gaps resulting from the Fig. 7. Example 2: a schematic view of the measurements large angle of the laser beam projection, a scan im- of the gaps on the western wall of the brewery (all age has been cut out and shown from the side op- measurements in centimeters) posite in relation to the measurements taken (from inside the building) (Fig. 8b). The table shows the measured. It is due the fact that the laser beam failed results of measuring the depth of the gaps based on a point cloud. However, it should be pointed out that to reach the rear edge of the gap (from the inner side these values are false as only the apparent depth was of the wall). Fig. 8a. A point cloud showing gaps in the façade resulting Fig. 8b. A section in the point cloud through the plane of from the crumbling of the building material. Tak- the scanned wall. Indicative depth of a gap in an ing measurements of the gaps (the table ) inverted view (the table) 46 architectura.actapol.net Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 Example 3: Damages caused by water and wind the pipes and gutters and to wash out the bricks and The southern façade seen from the court of the brew- the mortar joints. The damaged surface is clearly ery compound. Numerous damages were observed visible on the point cloud (Fig. 9b). Based on the here, caused mainly by water and wind. One of the scan, its area was estimated to cover ca. 90 cm . The analysed elements was a pillar between windows, damage starts at the height of 355 cm and ends at featuring water-washed bricks and mortar joints 455 cm (the table). The laser beam opening angle (Fig. 9a). This condition of the pillar results prob- ranges between 18 and 27° (Fig. 10) and was not of ably from a leaky system for removing rainwater great importance for measuring the damaged area in from the roof, causing the rainwater to flow out of the point cloud. Fig. 9a. Digital image of the washed-out bricks and mortar Fig. 9b. Washed-out bricks and mortar joint in the point joints cloud. The measurements are presented in the table Fig. 10. Example 3: a diagram of measuring the dam- ages on the southern wall of the building (be- sides angles, measurements in centimeters) architectura.actapol.net 47 Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 Table. List of all parameters of the damages presented in the study Example 3 Example 1 Example 2 Parameter Washed-out Crack Missing bricks material Gap 1: 29 Height [cm] 300 Gap 2: 38 130 Gap 3: 27 Gap 1: 43 Width [cm] 1–3 Gap 2: 56 70 Gap 3: 29 Gap 1: 28 Estimated depth [cm] – Gap 2: 43 – Gap 3: 33 Gap 1: 1247 Gap area [cm]23 Gap 2: 2128 9 100 Gap 3: 783 Distance between the scanner and the analysed damage [cm] 350 631 550 Height at which the damage is located [cm] 0–300 664–818 335–435 Angle between the laser beam and the analysed surface [°] from –25 to +22 from +39 to +47 from +18 to +27 Instrument height [cm] 161 161 161 Unreliable depth given as an example of actions performed on a point cloud. Evaluation of the measuring method difficult in this case, especially with regard to damages Over 60 damages on the façade of the brewery build- situated at a height. It would have also required using ing were identified during the survey, mostly corro- ladders or scaffoldings, which would have been con- sion and cavities resulting from destruction and lack of nected with a threat of a fall. In addition, using a scaf- repairs. In addition, numerous cracks in the walls were folding would have required attaching it to the build- discovered, possibly due to the instability of the soil, ing, which might have caused additional damages on but most likely due to the intensive vehicle traffic on it. This is always a significant issue, especially where the nearby regional road. a historical building is concerned. Moreover, some of the bricks are corroded and the Therefore, the survey was conducted using a 3D mortar joints are washed out. These damages do not laser scanner, which allows collecting the required form any regular pattern. Some of them are small and data in a non-invasive way, without posing any risk invisible at first glance, but some cover an area of up to the operator. However, a scanner is not an ideal de- to a few square meters. The table contains a list of pa- vice. A measuring station should be planned such as to rameters obtained by means of measuring selected ele- ensure that the laser beam does not hit an object at a ments in the point cloud. too big angle. Elements situated at a height should be The study presents three examples representing all measured from a bigger distance. This helps decrease of the analyses performed on the object. A significant the beam angle and allows deeper penetration of such difficulty in identifying and recording damages on an element. Placing a scanner too close to an object and object is inaccessibility of its individual elements. Tak- thus using too big angle of the laser results in the light ing measurements with use of traditional methods, e.g. beam failing to reach the details which are situated by means of tapes and gap gauges, would have been high above the ground or are concave. The result- 48 architectura.actapol.net Pawłowicz, J. A. (2021). Digital survey of damages on the façade of a historical building. Acta Sci. Pol. Architectura, 20 (2), 41–50. doi: 10.22630/ASPA.2021.20.2.13 ing point cloud is then incomplete (blind spots). It is REFERENCES therefore confirmed that the most efficient scanning Bernat, M., Byzdra, A., Chmielecki, M., Laskowski, P., occurs when the scanner is positioned as close as pos- Orzechowski, J., Rzepa, S., Szulwic, J. & Ziółkowski P. sible to the perpendicularity relative to the plane being (2016). Zastosowanie naziemnego skaningu laserowe- scanned. 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(2015). Analiza org/10.1016/S0924-2716(99)00011-8 statystyczna wartości Intensity (TLS) zarejestrowanych Wujanz, D., Burger, M., Tschirschwitz, F., Nietzschmann, na powierzchni konstrukcji betonowej. In M. Kwaśniak T., Neitzel, F. & Kersten, T. (2018). Determination of (Ed.), Techniki inwentaryzacji i monitoringu obiektów Intensity-Based Stochastic Models for Terrestrial Laser inżynierskich (pp. 90–105). Warszawa, Wydział Geode- Scanners Utilising 3D-Point Clouds. Sensors, 18 (7), zji i Kartografii Politechniki Warszawskiej. 2187. https://doi.org/10.3390/s18072187 CYFROWA INWENTARYZACJA USZKODZEŃ ELEWACJI BUDYNKU ZABYTKOWEGO STRESZCZENIE W pracy przedstawiono zastosowanie trójwymiarowego naziemnego skaningu laserowego (TLS) w ocenie stanu technicznego budynku zabytkowego na przykładzie browaru zlokalizowanego w Szczytnie (Polska). Wszystkie prace związane z uzyskaniem cyfrowej bazy danych wykonywano skanerem laserowym Leica ScanStation C10. Zakres prac obejmował pozyskanie i połącznie danych ze skaningu, a następnie określenie na ich podstawie skali uszkodzeń w wirtualnym obrazie budowli. W artykule omówiono skuteczność wy- korzystania skanera laserowego przy inwentaryzacji uszkodzeń obiektu zabytkowego. Podczas pomiarów napotkano na liczne ograniczenia, takie jak: trudne usytuowanie stanowisk, ruch na ulicach, ingerencja osób postronnych i niesprzyjające warunki atmosferyczne. Zastosowanie metody TLS wykorzystującej skaner im- pulsowy pozwala jednak na szybkie zdigitalizowanie całego obiektu, co przy inwentaryzacji dużych budyn- ków jest bardzo ważne. Warto dodać, że metoda ta jest jedną z nielicznych, która umożliwia inwentaryzację punktów trudno dostępnych, na przykład połaci dachowych czy wież, z poziomu terenu. Skaner laserowy doskonale nadaje się do cyfrowej inwentaryzacji obiektów zabytkowych. Szczególnie świetnie sprawdza się przy pomiarach uszkodzeń czy detali architektonicznych. Cyfrowe dane zebrane w terenie mogą być anali- zowane przed komputerem w komfortowych warunkach. Niewątpliwą wadą skaningu laserowego jest wystę- powanie dużej ilości danych przypadkowych i niepożądanych. Wiąże się to z wykonaniem pracochłonnej fil- tracji chmury punktów. Zdigitalizowane dane ułatwiają procedurę badawczą, ponieważ umożliwiają pomiary skomplikowanych obiektów przy zachowaniu maksymalnej szczegółowości i w kameralnych warunkach. Słowa kluczowe: naziemny skaning laserowy (TLS), chmura punktów, stan techniczny budynku, remont budynku, building information model (BIM) 50 architectura.actapol.net

Journal

Acta Scientiarum Polonorum Architecturade Gruyter

Published: Jun 1, 2021

Keywords: terrestrial laser scanning (TLS); point cloud; technical condition of a building; building redeco-ration; building information model (BIM)

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