Laserbasert oppmåling av bygningsobjekter og bygninger

Building information models (BIMs) for facility management is gaining interest. Different technologies for collecting the raw material to extract such model are in rapid development. The most common technologies are based on images, structure light, laser or a combination of these. The new technologies have the potential to provide efficient data collection, but not necessarily at the same accuracy compared to the traditional methods. This thesis has explored how to rapidly establish a BIM for an existing building. This was done by investigating two different aspects related to this task. The first aspect was related to product specification and provide a framework for ordering and controlling a laser-based survey of a building. The second aspect explores how a laser-based system could be used to rapidly survey an existing building. Through the thesis and the first aspect, it is shown that the Norwegian survey community is lacking an unambiguous product specification for building surveys performed for BIM extraction and that the survey seldomly is adequately controlled. Based on these findings a product specification has been developed in cooperation with building owners. This cooperation made it possible to test the product specification in real projects. The product specification was developed through three different versions. The zero version was presented at the World Building Congress in 2016 and was tested in a renovation project at the Norwegian University of Life Sciences. The evaluation of the project led to the first version that was used in a framework competition arranged by Ullensaker municipality in the south-east of Norway. The result led to the second and final version of the product specification. The proposed product specification follows a simplified transaction pattern between the customer and the producer. The focus has been on the customer's request for a building survey suitable for BIM extraction and the customer's acceptance actions when the building survey is delivered. The acceptance actions are based on well–known standards created by the Norwegian Mapping Authority. The customer request is based on the acceptance actions. This ensures that every requirements can be verified in the accepting stage. The main purposes of the product specification were to ensure reliable results and to minimize the difference between the customer request and the producer’s delivery. Additionally, an unambiguous product specification can ensure a fair competition situation between the producers and give the producers the possibility to select the best-suited technology. The second aspect is related to how a building can be efficiently surveyed and explores how this could be done with a laser-based system. A human carried survey system was developed through three stages. The first and second stages focused on circle shaped objects and were realized in cooperation with the Faculty of Environmental Sciences and Natural Resource Management at the Norwegian University of Life Sciences. The system surveyed tree diameter at breast height within sample plots in size 250-500 m2. The system was able to detect 87.5% of the trees with a mean difference of 0.1 cm, and a root mean square of 2.2 cm. The novel aspect is related to how the trees are segmented and how the diameters are estimated without losing precision due to degraded pose solution. The result can be used in forestry inventory projects together with airborne laser surveys. The third stage was made for indoor measurements. The main focus was on how to aid the navigation solution in the absence of Global Navigation Satellite System signals. The method divides the laser point measurements into small time frames. For each time frame, the laser points were automatically classified into column, walls, floor, and ceiling. This information was used to support a scan matching method called semantic-assisted normal distributions transform. The result from the scan matching was used to create a trajectory of the walking path followed during data capture. This result was fed back into the inertial navigation processing to aid the solution when the system was located inside the building. This gives the inertial navigation process the ability to reject scan matching failures. The novel method was able to improve the survey accuracy from a maximum deviation of 12.6 m to 1.1 m. The third stage had two different Inertial Measurement Units (IMU) installed. The most accurate system was a tactical graded IMU, and the lowest accurate system was an automotive graded IMU. With the proposed method, the automotive graded system was able to perform at a higher level than a standalone tactical graded solution.Interessen for å bruke BygningsInformasjonsModeller (BIMer) i forvaltning, drift og vedlikehold av bygninger er økende. Ulike teknologier for innsamling av data for å etablere slike modeller er i rask utvikling. De vanligste teknologiene er basert på bilder, strukturert lys, laser eller en kombinasjon av disse. Ny teknologi utfører målingene veldig effektivt, men ikke med samme nøyaktighet som tradisjoneller metoder. Denne studien har undersøkt hvordan en raskt kan etablere en BIM i et eksisterende bygg. Dette ble gjort ved å utforske to ulike aspekter av problemstillingen. Det første aspektet ser på produktspesifikasjon og foreslår et rammeverk til bruk ved bestilling og kontroll av laser-basert innmåling av eksisterende bygning. Det andre aspektet utforsker hvordan et laser-basert system raskt kan måle opp eksisterende bygg.The Norwegian Building Authority, Cautus Geo AS and Geomatikk survey have kindly founded parts of the studies

Comparing Mobile Laser Scanner and manual measurements for dendrometric variables estimation in a black pine (Pinus nigra Arn.) plantation

The growing demand of ecosystem services provided by forests increased the need for fast and accurate field survey. The recent technological innovations fostered the application of geomatic tools and processes to different fields of the forestry sector. In this study we compared the efficiency and the accuracy of Mobile Laser Scanner (MLS), combined with Simultaneous Localization and Mapping (SLAM) technology, and traditional field survey for the mensuration of main forest dendrometric variables like stem diameter at breast height (DBH), individual tree height (H), crown base height (CBH) and branch-free stem volume (VOL). With ground truth measurements taken from 50 felled trees, we tested the applicability of MLS technology for individual tree parameters esti-mation in a conifer plantation in central Italy. Our results showed no bias of DBH estimates and the corre-sponding RMSE was equal to 10.8% (2.7 cm). H and CBH measured with MLS were underestimated compared to the ground truth (bias of-8.6% for H and-13.3% for CBH). VOL values showed a bias and a RMSE of-4.1% (-0.01 m(3)) and 12.4% (0.04 m3) respectively. Tree height is not perfectly estimated due to laser obstruction by crowns layer, but the acquisition speed of this survey, joined with a suitable accuracy of parameters extraction, suggests sufficient suitability of the method for operational applications in simple forest structures (e.g. one-layered stands)

Estimation of forest variables using airborne laser scanning

Airborne laser scanning can provide three-dimensional measurements of the forest canopy with high efficiency and precision. There are presently a large number of airborne laser scanning instruments in operation. The aims of the studies reported in this thesis were, to develop and validate methods for estimation of forest variables using laser data, and to investigate the influence of laser system parameters on the estimates. All studies were carried out in hemi-boreal forest at a test area in southwestern Sweden (lat. 58°30’N, long. 13°40’ E). Forest variables were estimated using regression models. On plot level, the Root Mean Square Error (RMSE) for mean tree height estimations ranged between 6% and 11% of the average value for different datasets and methods. The RMSE for stem volume estimations ranged between 19% and 26% of the average value for different datasets and methods. On stand level (area 0.64 ha), the RMSE was 3% and 11% of the average value for mean tree height and stem volume estimations, respectively. A simulation model was used to investigate the effect of different scanning angles on laser measurement of tree height and canopy closure. The effect of different scanning angles was different within different simulated forest types, e.g., different tree species. High resolution laser data were used for detection of individual trees. In total, 71% of the field measurements were detected representing 91% of the total stem volume. Height and crown diameter of the detected trees could be estimated with a RMSE of 0.63 m and 0.61 m, respectively. The magnitude of the height estimation errors was similar to what is usually achieved using field inventory. Using different laser footprint diameters (0.26 to 3.68 m) gave similar estimation accuracies. The tree species Norway spruce (Picea abies L. Karst.) and Scots pine (Pinus sylvestris L.) were discriminated at individual tree level with an accuracy of 95%. The results in this thesis show that airborne laser scanners are useful as forest inventory tools. Forest variables can be estimated on tree level, plot level and stand level with similar accuracies as traditional field inventories

Airborne and Terrestrial Laser Scanning Data for the Assessment of Standing and Lying Deadwood: Current Situation and New Perspectives

LiDAR technology is finding uses in the forest sector, not only for surveys in producing forests but also as a tool to gain a deeper understanding of the importance of the three-dimensional component of forest environments. Developments of platforms and sensors in the last decades have highlighted the capacity of this technology to catch relevant details, even at finer scales. This drives its usage towards more ecological topics and applications for forest management. In recent years, nature protection policies have been focusing on deadwood as a key element for the health of forest ecosystems and wide-scale assessments are necessary for the planning process on a landscape scale. Initial studies showed promising results in the identification of bigger deadwood components (e.g., snags, logs, stumps), employing data not specifically collected for the purpose. Nevertheless, many efforts should still be made to transfer the available methodologies to an operational level. Newly available platforms (e.g., Mobile Laser Scanner) and sensors (e.g., Multispectral Laser Scanner) might provide new opportunities for this field of study in the near future

Terrestrial laser scanning for vegetation analyses with a special focus on savannas

Savannas are heterogeneous ecosystems, composed of varied spatial combinations and proportions of woody and herbaceous vegetation. Most field-based inventory and remote sensing methods fail to account for the lower stratum vegetation (i.e., shrubs and grasses), and are thus underrepresenting the carbon storage potential of savanna ecosystems. For detailed analyses at the local scale, Terrestrial Laser Scanning (TLS) has proven to be a promising remote sensing technology over the past decade. Accordingly, several review articles already exist on the use of TLS for characterizing 3D vegetation structure. However, a gap exists on the spatial concentrations of TLS studies according to biome for accurate vegetation structure estimation. A comprehensive review was conducted through a meta-analysis of 113 relevant research articles using 18 attributes. The review covered a range of aspects, including the global distribution of TLS studies, parameters retrieved from TLS point clouds and retrieval methods. The review also examined the relationship between the TLS retrieval method and the overall accuracy in parameter extraction. To date, TLS has mainly been used to characterize vegetation in temperate, boreal/taiga and tropical forests, with only little emphasis on savannas. TLS studies in the savanna focused on the extraction of very few vegetation parameters (e.g., DBH and height) and did not consider the shrub contribution to the overall Above Ground Biomass (AGB). Future work should therefore focus on developing new and adjusting existing algorithms for vegetation parameter extraction in the savanna biome, improving predictive AGB models through 3D reconstructions of savanna trees and shrubs as well as quantifying AGB change through the application of multi-temporal TLS. The integration of data from various sources and platforms e.g., TLS with airborne LiDAR is recommended for improved vegetation parameter extraction (including AGB) at larger spatial scales. The review highlights the huge potential of TLS for accurate savanna vegetation extraction by discussing TLS opportunities, challenges and potential future research in the savanna biome

Terrestrial laser scanning in forest inventories

AbstractDecision making on forest resources relies on the precise information that is collected using inventory. There are many different kinds of forest inventory techniques that can be applied depending on the goal, scale, resources and the required accuracy. Most of the forest inventories are based on field sample. Therefore, the accuracy of the forest inventories depends on the quality and quantity of the field sample. Conventionally, field sample has been measured using simple tools. When map is required, remote sensing materials are needed. Terrestrial laser scanning (TLS) provides a measurement technique that can acquire millimeter-level of detail from the surrounding area, which allows rapid, automatic and periodical estimates of many important forest inventory attributes. It is expected that TLS will be operationally used in forest inventories as soon as the appropriate software becomes available, best practices become known and general knowledge of these findings becomes more wide spread. Meanwhile, mobile laser scanning, personal laser scanning, and image-based point clouds became capable of capturing similar terrestrial point cloud data as TLS. This paper reviews the advances of applying TLS in forest inventories, discusses its properties with reference to other related techniques and discusses the future prospects of this technique

Co-registration of single tree maps and data captured by a moving sensor using stem diameter weighted linking

A new method for the co-registration of single tree data in forest stands and forest plots applicable to static as well as dynamic data capture is presented. This method consists of a stem diameter weighted linking algorithm that improves the linking accuracy when operating on diverse diameter stands with stem position errors in the single tree detectors. A co-registration quality metric threshold, QT, is also introduced which makes it possible to discriminate between correct and incorrect stem map co-registrations with high probability (>99%). These two features are combined to a simultaneous location and mapping-based co-registration method that operates with high linking accuracy and that can handle sensors with drifting errors and signal bias. A test with simulated data shows that the method has an 89.35% detection rate. The statistics of different settings in a simulation study are presented, where the effect of stem density and position errors were investigated. A test case with real sensor data from a forest stand shows that the average nearest neighbor distances decreased from 1.90 m to 0.51 m, which indicates the feasibility of this method

Automatic tree detection and attribute characterization using portable terrestrial lidar

Currently, the implementation of portable laser scanners (PLS) in forest inventories is being studied, since they allow for significantly reduced field-work time and costs when compared to the traditional inventory methods and other LiDAR systems. However, it has been shown that their operability and efficiency are dependent upon the species assessed, and therefore, there is a need for more research assessing different types of stands and species. Additionally, a few studies have been conducted in Eucalyptus stands, one of the tree genus that is most commonly planted around the world. In this study, a PLS system was tested in a Eucalyptus globulus stand to obtain different metrics of individual trees. An automatic methodology to obtain inventory data (individual tree positions, DBH, diameter at different heights, and height of individual trees) was developed using public domain software. The results were compared to results obtained with a static terrestrial laser scanner (TLS). The methodology was able to identify 100% of the trees present in the stand in both the PLS and TLS point clouds. For the PLS point cloud, the RMSE of the DBH obtained was 0.0716, and for the TLS point cloud, it was 0.176. The RMSE for height for the PLS point cloud was 3.415 m, while for the PLS point cloud, it was 10.712 m. This study demonstrates the applicability of PLS systems for the estimation of the metrics of individual trees in adult Eucalyptus globulus stands.Agencia Estatal de Investigación | Ref. PID2019-111581RB-I00Ministerio de Ciencia, Innovación y Universidades | Ref. FPU19/02054Universidade de Vigo/CISU