Auditing an urban park deck with 3D geovisualization—A comparison of in-situ and VR walk-along interviews

Virtual reality-based urban audit methods are gaining increasing attention; however, most virtual urban audit studies have focused on panoramic views. The 3D city model-based geovisualizations have remained until now rather unexplored in user studies for urban audits and for communicative urban planning. We explored the feasibility of a 3D geovisualization-based urban audit in virtual reality (VR) for assessing the perceived quality of an urban park deck in Helsinki, Finland. For this purpose, we created a photorealistic and geometrically accurate 3D model (Bryga 3D) based on photogrammetric and laser scanning data. Bryga 3D was implemented on a game engine to be viewed with a head-mounted VR display. Bryga 3D's ability to convey information in a subjective urban audit, that is, subjectively perceived affordances of a park deck, was tested in a walk-along interview study comparing auditing in situ and via the VR method. A comparison of the results with in-situ (n = 13) and VR interviews (n = 21) show that the perception of several tangible elements, such as spatial division, landforms, paths, and chairs when using Bryga VR was similar to when performed in situ. Perception of vegetation was weaker in VR in terms of its detailed quality, which somewhat affected the presented development ideas and assessment of the seasonal context. Also, weaker perception of the surroundings and city context affected the results in VR. However, considering that Bryga 3D presents an example of a highly automated 3D city modeling process conducted with minimal manual work, its results are encouraging for future attempts to advance such realizations for the purposes of communicative urban planning. 3D geovisualization-based virtual audits could be used when urban green space audits are not possible or when they are demanding to implement in situ.</p

Performance Assessment of Reference Modelling Methods for Defect Evaluation in Asphalt Concrete

The deterioration of road conditions and increasing repair deficits pose challenges for the maintenance of reliable road infrastructure, and thus threaten, for example, safety and the fluent flow of traffic. Improved and more efficient procedures for maintenance are required, and these require improved knowledge of road conditions, i.e., improved data. Three-dimensional mapping presents possibilities for large-scale collection of data on road surfaces and automatic evaluation of maintenance needs. However, the development and, specifically, evaluation of large-scale mobile methods requires reliable references. To evaluate possibilities for close-range, static, high-resolution, three-dimensional measurement of road surfaces for reference use, three measurement methods and five instrumentations are investigated: terrestrial laser scanning (TLS, Leica RTC360), photogrammetry using high-resolution professional-grade cameras (Nikon D800 and D810E), photogrammetry using an industrial camera (FLIR Grasshopper GS3-U3-120S6C-C), and structured-light handheld scanners Artec Leo and Faro Freestyle. High-resolution photogrammetry is established as reference based on laboratory measurements and point density. The instrumentations are compared against one another using cross-sections, point-point distances, and ability to obtain key metrics of defects, and a qualitative assessment of the processing procedures for each is carried out. It is found that photogrammetric models provide the highest resolutions (10-50 million points per m2) and photogrammetric and TLS approaches perform robustly in precision with consistent sub-millimeter offsets relative to one another, while handheld scanners perform relatively inconsistently. A discussion on the practical implications of using each of the examined instrumentations is presented

The suitability of handheld simultaneous localization and mapping laser scanners for modelling the geometry of a building

Tässä tutkimuksessa selvitetään samanaikaisesti paikantavan ja kartoittavan (SLAM) käsiskannerin soveltuvuutta rakennuksen geometrian mallintamiseen ja tällaisten mallien luomisen nopeuttamiseen. Tutkimus keskittyi SLAM-käsiskannereihin, joista tarkemmin tutkitaan ZEB-REVO-käsiskanneria. Tämän käsiskannerin soveltuvuuden tutkimiseksi rakennuksen geometriamallin luomiseen jaettiin tutkimus kirjallisuuskatsaukseen ja kokeellisiin tutkimuksiin. Kirjallisuuskatsauksessa selvitettiin rakennuksen geometriamallien luontia, SLAM-käsiskannerien taustoja ja ZEB-REVO:n toimintaperiaatteita. Kokeellisissa tutkimuksissa selvitettiin erillisillä analyyseillä useista mittauskohteista ZEB-REVO:n soveltuvuutta BIM-mallinnukseen. Tutkimus ei kuitenkaan sisällä BIM-mallin mallinnusvaihetta. Kokeellisissa tutkimuksissa selvisi ZEB-REVO:n soveltuvan hyvin rakennuksen geometrian mallintamiseen vain optimaalisten kohteiden kohdalla. Näiden tulosten pohjalta ZEB-REVO tarjoaa kuitenkin hyvän BIM-mallinnustarkkuuden vaatimaansa ajankäyttöön nähden. Lisäksi tarkkuutta voidaan verrata GSA:n (General Services Administration) ohjeellisiin mallinnusraja-arvoihin, joiden pohjalta havaittiin kohteen vaikuttavan mallinnuksen lopputulokseen. Tällöin optimaalinen kohde tuottaa koko rakennuksesta hyvän BIM-mallin, mutta sisätiloista tarkkuus jää raja-arvojen ulkopuolelle. Kuitenkin epäoptimaalisesta kohteesta, joita ovat SLAM-algoritmille sopimattomat tilat, BIM-mallin tuottaminen on mahdollista selvästi heikommalla tarkkuudella. Lisäksi tuloksista havaitaan ZEB-REVO:n mallinnuksen ominaisuuksien ja mittausasetusten vaikuttavan lopputulokseen. Tällaisia ominaisuuksia ovat muun muassa ZEB-REVO:n suhteellisen vähäinen kohina, SLAM-algoritmin hyvä paikannustarkkuus eri tilojen kohteiden välillä ja yli 2cm korkeiden yksityiskohtien havaitseminen. Lisäksi mittausasetuksiltaan tulokset tukevat laitevalmistajan ohjeiden mukaista mittausetäisyyttä ja rauhallista etenemistä.This research determines the suitability of handheld simultaneous localization and mapping (SLAM) laser scanners for modelling the geometry of a building faster than with traditional methods. The research focuses on handheld SLAM laser scanners and the biggest focus is on the ZEB-REVO laser scanner. For the suitability of this laser scanner, the research was divided into a literature review and a practical research. The literature review explains how to make geometry models of buildings, the backgrounds of the SLAM laser scanners and the operational principle of ZEB-REVO. In the practical research, the suitability of ZEB-REVO for BIM modelling was tested by analysing results from different measurement subjects. However, the research do not include the modelling section of the preparation of the BIM. Based on the results of the practical research it can be concluded that the suitability of ZEB-REVO for modelling the geometry of the building is good when the subject is optimal. ZEB-REVO provides good accuracy for BIM modelling when we take to account the time usage of the modelling process. In addition to accuracy, it can be compared with a directive modelling the boundary values of GSA (General Services Administration). On the grounds of these comparisons, the subject impacts the accuracy of the final model. In these cases, the optimal subject gives a good BIM model for the whole building. However, the accuracy of the interior is bigger than the boundary values. Though, even in the non-optimal case producing the BIM model is possible, only with weaker accuracy. These non-optimal subjects are environments where SLAM algorithm does not work correctly. In addition these factors, some characteristics of ZEB-REVO affect the final model. ZEB-REVO features a relatively small noise, a SLAM algorithm which can locate subjects from different environments well together and is capable of recognizing details more extruded than 2 cm. Additionally this study confirms the manufacturer’s recommendation of measurement distance and movement speed

Samanaikaisesti paikantavien ja kartoittavien käsilaserkeilainten mittausstrategian ja jälkiprosessoinnin parantaminen

Three-dimensional (3D) data technologies such as laser scanning have automated the data collection of 3D mapping. However, built environments include ones without global navigation satellite system access, and where terrestrial laser scanning of the environment would be laborious, time-consuming, and prone to occlusions. In these environments 3D mapping could instead be executed with simultaneous localization and mapping (SLAM) laser scanners (LSs). Regrettably, the effects of the these measurement strategies and post-processing of SLAM LS systems have been rarely evaluated. This dissertation investigated and developed the workflow of SLAM LS systems for 3D mapping in a built environment, with the hypothesis that by evolving measurement paths and practices as data integration and post-processing methods, SLAM LS systems are more suitable to be applied for 3D mapping. The measurement paths and practices were studied in use cases with two commercial SLAM LS systems. The experiments investigated the effect of the measurement paths and existing features in the environment. The integration method utilized a SLAM LS point cloud as supporting data for terrestrial laser scanner (TLS) point cloud registration. In addition, the post-processing was investigated by demonstrating the drift error reduction. Based on the results, the measurement paths and practices can be evolved with the utilization of a well-planned measurement path. The measurement path should include internal loops based on the environment that it is intended to measure. Stable environments have better point cloud ac- curacy with a minimal number of internal loops. In contrast, unstable environments require more internal loops. The overall path in most built environments should combine these practices. In ad- dition, the internal loops should be located around the landmarks, the diameter of the internal loop should be scaled beside the space, and SLAM LS should be facing the middle of the environment during the internal loop. The environments include dynamic objects, the uneven distribution of the landmarks for the SLAM algorithm or unembellished should be avoided. If avoiding such environment is impossible, the measurement range of SLAM LS should be chosen accordingly, or additional landmarks should be added. These can prevent the drift error from occurring. However, the drift error appeared to be onedimensional and can be reduced with commercial software from the SLAM LS point cloud. The results indicate that the integration of SLAM LS and TLS pro- moted the 3D reconstruction with accuracy optimization in required locations and a reduction of measurement time by 72%.With the evolved measurement paths and practices, the SLAM LS systems could be utilized for 3D mapping in built environments. The requirements of the 3D reconstructions can be reached by understanding the measurement methods of the SLAM LS.Kolmiulotteiset mittausteknologiat kuten laserkeilaus ovat automatisoineet 3D-kartoituksen. Nykyisillä menetelmillä on kuitenkin ongelmia ympäristöissä, joihin satelliittipaikannusjärjestelmä  ei ylety. Maalaserkeilaus (TLS) näissä ympäristöissä on työlästä, aikaa vievää ja aineistoon jää helposti aukkoja. Tällöin voidaan hyödyntää samanaikaisesti paikantavia ja kartoittavia (SLAM) laser-keilaimia. Valitettavasti, SLAM-laserkeilaimien mittausmenetelmien ja jälkiprosessoinnin vaikutuksia ei ole juurikaan arvioitu. Väitöskirjassa tutkittiin ja kehitettiin SLAM-laserkeilaimien soveltuvuutta rakennetun ympäristön 3D-kartoittamiseen. Tämä toteutettiin hypoteesin avulla, jonka mukaan SLAM-laserkeilaimien mittausreittien ja toimintatapojen kuten aineistojen yhdistämisen ja jälkiprosessoinnin kehittämisellä ne soveltuvat paremmin 3D-kartoitukseen. Mittausreittejä ja toimintatapoja tutkittiin kahdessa käyttötapauksessa hyödyntäen kahta kaupallista SLAM-laserkeilainta. Kokeiluissa tutkittiin mittausreitin ja ympäristön piirteiden vaikutusta SLAM-laserkeilaukseen sekä integraatiomenetelmää, jossa SLAM-laserkeilauksen pistepilveä hyödynnettiin tukiaineistona TLS-pistepilvien rekisteröinnissä. Lisäksi tutkittiin paikannuksen drift virheen pienentämistä jälkiprosessoinnissa. Työn tulokset osoittivat useita SLAM-laserkeilausmittausten suorituskyvyn kehitystapoja. Mittausreitin tulisi sisältää ympäristöstä riippuen sisäisiä kierroksia. Vakaissa ympäristöissä saadaan paras pistepilven tarkkuus tekemällä mahdollisimman vähän sisäisiä kierroksia, kun taas epävaikaissa ympäristöissä niitä tarvitaan enemmän. Monissa rakennetun ympäristön kohteissa mittausreitti koostuu näiden yhdistelmästä. Lisäksi mittausreitin sisäisten kierroksien tulisi kiertää ympäristön kohteita ja halkaisijan koko tulisi valita ympäristön mukaan. Näiden lisäksi SLAM-laserkeilaimen näkymäalue tulisi suunnata sisäisen kierroksen keskelle. Ympäristöjä, jotka sisältävät liikettä, epätasaisesti jakautuneita maamerkkejä, joita SLAM-algoritmi hyödyntää kartoituksessa tai avoimia alueita, tulisi välttää SLAM-laserkeilaimilla. Mikäli välttäminen ei ole mahdollista, SLAM-laser- keilaimen maksimimittausetäisyys tulisi valita tarpeen mukaan tai ympäristöön tulisi lisätä maamerkkejä. Näiden avulla voidaan välttää vääristymiä. Kuitenkin vääristymät olivat yksisuuntaisia ja niitä voidaan vähentää SLAM-laserkeilaimien pistepilvistä jälkiprosessointimenetelmillä. SLAM-laserkeilaimen ja TLS yhdistämisen tuloksien pohjalta 3D-rekonstruktioita voidaan tuottaa tarpeen mukaan optimoiduilla tarkkuuksilla ja työssä tehdyssä koetyössä mittaamiseen kului 72% vähemmän aikaa. Työn tulosten mukaan mittausreittejä ja toimintatapoja kehittämällä SLAM-laserkeilaimia voidaan hyödyntää rakennetun ympäristön 3D-kartoitukseen entistä tehokkaammin, jolloin erilaisten 3D-mittaussovellusten vaatimukset voidaan saavuttaa paremmin

Drift analysis and sectional post-processing of indoor simultaneous localization and mapping (SLAM)-based laser scanning data

Even though the SLAM laser scanners (LSs) have the required resolution for construction analysis, a drift error has been detected in georeferencing phase of the data processing. The reduction of drift error in SLAM LSs with third-party software has not been studied. This paper demonstrates the drift error behavior of commercial SLAM LSs and their correction with sectional post-processing methods, and shows that the drift error is mainly in a vertical direction, and it is largest in the middle of the trajectory. The drift error was reduced from 10.6 cm to 0.2 cm. Circa 30 s length sections have better results than larger sections with non-rigid transformation algorithm. The method has shown potential to improve the quality and cost-effectiveness of multitemporal construction documentation. In addition, locations of additional control points were analyzed to prevent drift error, with adjustments to the walking path

Measurement Strategies for Street-Level SLAM Laser Scanning of Urban Environments

Data collection for street-level mapping is currently executed with terrestrial (TLS) or mobile laser scanners (MLS). However, these methods have disadvantages such as TLS requiring a lot of time and MLS being dependent on the global navigation satellite system (GNSS) and an inertial measurement unit (IMU). These are not problems if we use simultaneous localization and mapping (SLAM) based laser scanners. We studied the utility of a SLAM ZEB-REVO scanner for mapping street-level objects in an urban environment by analyzing the geometric and visual differences with a TLS reference. In addition to this, we examined the influence of traffic on the measurement strategy. The results of the study showed that SLAM-based laser scanners can be used for street-level mapping. However, the measurement strategy affects the point clouds. The strategy of walking trajectory in loops produced a 2 cm RMS and 4-6 mm mode of error even in not optimal situations of the sensor in the urban environment. However, it was possible to get an RMS under 2.2 cm and a 32 cm mode of error with other measurement strategies.Peer reviewe

The combined use of SLAM laser scanning and TLS for the 3D indoor mapping

Funding Information: This research was funded by Aalto University School of Engineering Tenure track (Digital Photogrammetry) funding, the Academy of Finland the Strategic Research Council projects, ?Competence-Based Growth Through Integrated Disruptive Technologies of 3D Digitalization, Robotics, Geospatial Information, and Image Processing/Computing?Point Cloud Ecosystem? (No. 293389, 314312), Academy of Finland project ?Quality4Roads? (No. 323783), project Profi5 ?Autonomous systems? (No. 326246), the European Social Fund (S21997) and the City of Helsinki Innovation fund. Publisher Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland.An efficient 3D survey of a complex indoor environment remains a challenging task, especially if the accuracy requirements for the geometric data are high for instance in building information modeling (BIM) or construction. The registration of non-overlapping terrestrial laser scanning (TLS) point clouds is laborious. We propose a novel indoor mapping strategy that uses a simultaneous localization and mapping (SLAM) laser scanner (LS) to support the building-scale registration of non-overlapping TLS point clouds in order to reconstruct comprehensive building floor/3D maps. This strategy improves efficiency since it allows georeferenced TLS data to only be collected from those parts of the building that require such accuracy. The rest of the building is measured with SLAM LS accuracy. Based on the results of the case study, the introduced method can locate non-overlapping TLS point clouds with an accuracy of 18–51 mm using target sphere comparison.Peer reviewe

Auditing an urban park deck with 3D geovisualization—A comparison of in-situ and VR walk-along interviews

Virtual reality-based urban audit methods are gaining increasing attention; however, most virtual urban audit studies have focused on panoramic views. The 3D city model-based geovisualizations have remained until now rather unexplored in user studies for urban audits and for communicative urban planning. We explored the feasibility of a 3D geovisualization-based urban audit in virtual reality (VR) for assessing the perceived quality of an urban park deck in Helsinki, Finland. For this purpose, we created a photorealistic and geometrically accurate 3D model (Bryga 3D) based on photogrammetric and laser scanning data. Bryga 3D was implemented on a game engine to be viewed with a head-mounted VR display. Bryga 3D’s ability to convey information in a subjective urban audit, that is, subjectively perceived affordances of a park deck, was tested in a walk-along interview study comparing auditing in situ and via the VR method. A comparison of the results with in-situ (n = 13) and VR interviews (n = 21) show that the perception of several tangible elements, such as spatial division, landforms, paths, and chairs when using Bryga VR was similar to when performed in situ. Perception of vegetation was weaker in VR in terms of its detailed quality, which somewhat affected the presented development ideas and assessment of the seasonal context. Also, weaker perception of the surroundings and city context affected the results in VR. However, considering that Bryga 3D presents an example of a highly automated 3D city modeling process conducted with minimal manual work, its results are encouraging for future attempts to advance such realizations for the purposes of communicative urban planning. 3D geovisualization-based virtual audits could be used when urban green space audits are not possible or when they are demanding to implement in situ

3D Point Cloud Data in Conveying Information for Local Green Factor Assessment

The importance of ensuring the adequacy of urban ecosystem services and green infrastructure has been widely highlighted in multidisciplinary research. Meanwhile, the consolidation of cities has been a dominant trend in urban development and has led to the development and implementation of the green factor tool in cities such as Berlin, Melbourne, and Helsinki. In this study, elements of the green factor tool were monitored with laser-scanned and photogrammetrically derived point cloud datasets encompassing a yard in Espoo, Finland. The results show that with the support of 3D point clouds, it is possible to support the monitoring of the local green infrastructure, including elements of smaller size in green areas and yards. However, point clouds generated by distinct means have differing abilities in conveying information on green elements, and canopy covers, for example, might hinder these abilities. Additionally, some green factor elements are more promising for 3D measurement-based monitoring than others,such as those with clear geometrical form. The results encourage the involvement of 3D measuring technologies for monitoring local urban green infrastructure (UGI), also of small scale.Peer reviewe